Bi3+ and Yb3+ codoped cubic Y2O3 phosphors are prepared by pechini sol-gel method. Strong near-infrared (NIR) emission around 980 nm from Yb3+ (2F5/2+2 F7/2) is observed under ultraviolet light excitation. A b...Bi3+ and Yb3+ codoped cubic Y2O3 phosphors are prepared by pechini sol-gel method. Strong near-infrared (NIR) emission around 980 nm from Yb3+ (2F5/2+2 F7/2) is observed under ultraviolet light excitation. A broad excitation band ranging from 320 to 360 nm, owing to the 6s2→6s6p transition of Bi3+ ions, is recorded when the Yb3+ emission is monitored, which suggests a very efficient energy transfer from Bi3+ ions to Yb3+ ions. The Yb3+ concentration dependences of both the Bi3+ and the Yb3+ emissions are investigated. The decay curve of Bi3+ emission under the excitation of 355 nm pulse laser is used to explore the Bi3+ →+Yb3+ energy transfer process. Cooperative energy transfer (CET) is discussed as a possible mechanism for the near-infrared emission.展开更多
A novel near-infrared (NIR) downconversion (DC) phosphor KSrPO4:Eu2+, Pr3+ is synthesized by the conventional high temperature solid-state reaction. The Eu2+ acts as an efficient sensitizer for Pr3+ in the KS...A novel near-infrared (NIR) downconversion (DC) phosphor KSrPO4:Eu2+, Pr3+ is synthesized by the conventional high temperature solid-state reaction. The Eu2+ acts as an efficient sensitizer for Pr3+ in the KSrPO4 host. With broad- band near-ultraviolet light excitation induced by the 4f→5d transition of Eu2+, the characteristic NIR emission of Pr3+, peaking at 974 nm and 1019 nm due to 3po →1G4 and 1G4→3H4 transitions, is generated as a result of the energy transfer from Eu2+ to Pr3+. The luminescence spectra in both the visible and the NIR regions and the decay lifetime curves of Eu2+ prove the energy transfer from Eu2+ to Pr3+. This Eu2+ and Pr3+ co-doped KSrPO4 phosphor may be a promising candidate to modify the spectral mismatch behavior of crystalline solar cells and sunlight.展开更多
The wide-band digital receiving systems require digital downconversion(DDC) with high data rate and short tuning time in order to intercept the narrow-band signals within broad tuning bandwidth. But these requirements...The wide-band digital receiving systems require digital downconversion(DDC) with high data rate and short tuning time in order to intercept the narrow-band signals within broad tuning bandwidth. But these requirements can not be met by the commercial DDC. In this paper an efficient implementation architecture is presented. It combines the flexibility of DFT tuning with the efficiency of the polyphase filter bank decomposition. By first decimating the data prior to filtering and mixing, this architecture gives a better solution to the mismatch between the lower hardware speed and high data rate. The computer simulations show the feasibility of this processing architecture.展开更多
We experimentally demonstrated the use of intelligent impairment equalization(IIE)for microwave downconversion link linearization in noncooperative systems.Such an equalizer is realized based on an artificial neural n...We experimentally demonstrated the use of intelligent impairment equalization(IIE)for microwave downconversion link linearization in noncooperative systems.Such an equalizer is realized based on an artificial neural network(ANN).Once the training process is completed,the inverse link transfer function can be determined.With the inverse transformation for the detected signal after transmission,the third-order intermodulation distortion components are suppressed significantly without requiring any prior information from an input RF signal.Furthermore,fast training speed is achieved,since the configuration of ANN-based equalizer is simple.Experimental results show that the spurious-free dynamic range of the proposed link is improved to 106.5 dB·Hz^(2/3),which is 11.3 dB higher than that of a link without IIE.Meanwhile,the training epochs reduce to only five,which has the potential to meet the practical engineering requirement.展开更多
All of the samples were synthesized by sol-gel methods.Two approaches to charge compensation,(i) 2Ca2+→Yb3++M+,where M+ is an alkali ion like Li+,Na+ and K+,and(ii) indirect charge compensation:3Ca2+→2...All of the samples were synthesized by sol-gel methods.Two approaches to charge compensation,(i) 2Ca2+→Yb3++M+,where M+ is an alkali ion like Li+,Na+ and K+,and(ii) indirect charge compensation:3Ca2+→2Yb3++vacancy,were studied in detail.It was found that charge compensation would be very beneficial for the growth of the grains,especially in Li+ ions added samples.All the grains were homogeneously spherical with less boundaries;in addition,a great variety of the absorption ability in different charge compensation samples were observed:in comparison with the phosphors without charge compensation,indirectly charge compensated and Li+ ions added phosphors showed much stronger absorption strength in the ultraviolet(UV) region whereas that of Na+ and K+ ions added samples was much weaker;moreover,measurements of the emission intensities showed that:in comparison with the phosphors without charge compensation,the visible emission intensity from MoO42-decreased a lot in indirectly charge compensated and Li+ ions added phosphors,whereas there was a remarkable increase of the near infrared(NIR) emission intensity from Yb3+ ions in the two types of samples under 266 nm excitation,implying more efficient energy transfer(ET) from MoO42-to Yb3+ ions;at last,measurements and analysis of the decay curves of the visible 495 nm emission were carried out,and it was found that the energy transfer from MoO42-to Yb3+ ions were more efficient in the two above types of phosphors.The theoretical quantum cutting(QC) efficiency was also improved greatly.Overall,the addition of Li+ ions would be very beneficial for the morphology of the powders in addition to the growth of the grains.It was advantageous to increase the downconversion(DC) quantum efficiency;however,indirect charge compensation would enhance the NIR emission intensity to the most for its strongest absorption ability in the UV region.展开更多
Tb3+ and Yb3+ codoped Lu2O3 nanophosphors were synthesized by the reverse-strike co-precipitation method. The obtained Lu2O3:Tb3+,Yb3+ nanophosphors were characterized by X-ray diffraction (XRD) and photolumine...Tb3+ and Yb3+ codoped Lu2O3 nanophosphors were synthesized by the reverse-strike co-precipitation method. The obtained Lu2O3:Tb3+,Yb3+ nanophosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra. The XRD results showed that all the prepared nanophosphors could be readily indexed to pure cubic phase of Lu2O3 and indicated good crystallinity. The Tb3+→Yb3+ energy transfer mechanisms in the UV-blue region in Lu2O3 nanophosphors were investigated. The experimental results showed that the strong visible emission around 543 nm from Tb3+ (5D4→7F5) and near-infrared (NIR) emission around 973 nm from Yb3+ (2F5/2→2F7/2) of Lu2O3:Tb3+,Yb3+ nanophosphors were observed under ultraviolet light excitation, respectively. Tb3+ could be effectively excited up to its 4f75d1 state and relaxed down to the 5D4 level, from which the energy was transferred cooperatively to two neighboring Yb3+. The Yb3+ concentration dependent luminescent properties and lifetimes of both the visible and NIR emissions were also studied. The lifetime of the visible emission decreased with the increase of Yb3+ concentration, verifying the efficient energy transfer from the Tb3+ to the Yb3+. Cooperative energy transfer (CET) from Tb3+ to Yb3+ was discussed as a possible mechanism for the near-infrared emission. When doped concentrations were 1 mol.% Tb3+ and 2 mol.% Yb3+, the intensity of NIR emission was the strongest.展开更多
An efficient near-infrared (NIR) downconversion (DC) by converting broadband ultraviolet (UV) into NIR was demon- strated in YVO4:Tma+,yb3+ phosphors. The phosphors were extensively characterized using variou...An efficient near-infrared (NIR) downconversion (DC) by converting broadband ultraviolet (UV) into NIR was demon- strated in YVO4:Tma+,yb3+ phosphors. The phosphors were extensively characterized using various methods such as X-ray diffrac- tion, photoluminescence excitation, photoluminescence spectra and decay lifetime to provide supporting evidence for DC process. Upon UV light varying from 260 to 350 nm or blue light (473 nm) excitation, an intense NIR emission of Yb3+ corresponding to tran- sition of 2Fs/2/5→2F7/2 peaking at 985 nm was generated. The visible emission, the NIR mission and the decay lifetime of the phosphors of various Yb3+ concentrations were investigated. Experimental results showed that the energy transfer from vanadate group to Yb3+ via Tm3+ was very efficient. Application of the broadband DC YVO4:Tma+,yb3+ phosphors might greatly enhance response of sili- con-based solar cells.展开更多
Exploiting microwave photonic(MWP)techniques to generate and distribute high-frequency millimeter-wave(mm-wave)signals,termed mm-wave radio over fiber(m-RoF)signals,holds considerable potential for achieving highdensi...Exploiting microwave photonic(MWP)techniques to generate and distribute high-frequency millimeter-wave(mm-wave)signals,termed mm-wave radio over fiber(m-RoF)signals,holds considerable potential for achieving highdensity and high-capacity fifth-generation and beyond networks.Herein,we experimentally validate a broadband m-RoF uplink fronthaul transmission system using the MWP downconversion concept,which comprises receiving and processing radio-frequency(RF)signals in the unlicensed V-band at around 60 GHz.The proposed system harnesses the simple cascaded modulator topology,in which an ultrawideband off-the-shelf Mach–Zehnder modulator(MZM)renders a simplestructured remote radio head by directly encoding the broadband 60 GHz uplink RF signal into the optical carrier.The nonlinear transfer function of another MZM at the center unit is explored to achieve subharmonic downconversion using cost-effective low-frequency local oscillator signals.Based on proof-of-concept experiments,mm-wave four quadrature amplitude modulation orthogonal frequency-division multiplexing signals centered at frequencies ranging from 51 GHz to 70 GHz are successfully downconverted into signals at the intermediate frequency(IF)of 1.4 GHz.In the case of 1.2 m mm-wave,free-space,and 5 km m-RoF transmissions,the obtained IF signals with a total bandwidth of 2.4 GHz achieve a bit-to-error ratio performance lower than the 7%hard-decision forward error correction limit of 3.8×10^(−3).A gross bit rate of 10 Gbit/s can be achieved over a total spectrum of up to 10 GHz,which fully covers the globally unlicensed V-band of 57-66 GHz.展开更多
We report on cooperative quantum cutting in Tb^3+- Yb^3+ codoped glass ceramics. Precipitation of BaF2 nanocrystals is confirmed by XRD and HRTEM analysis. Near-infrared emission due to transition of Yb^3+ ions und...We report on cooperative quantum cutting in Tb^3+- Yb^3+ codoped glass ceramics. Precipitation of BaF2 nanocrystals is confirmed by XRD and HRTEM analysis. Near-infrared emission due to transition of Yb^3+ ions under 485 nm excitation indicates cooperative energy transfer from Tb^3+ to Yb^3+. The quantum efficiency of this process reaches 145%. The realization of quantum cutting in glass ceramics may have promising applications in solar cells.展开更多
Ce3+, Yb3+ co-doped Y3Al5O12 films were prepared by pulse laser deposition. X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectra were used to characterize their structural and luminescent p...Ce3+, Yb3+ co-doped Y3Al5O12 films were prepared by pulse laser deposition. X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectra were used to characterize their structural and luminescent properties. Near-infrared quantum cutting from the films was observed via a cooperative energy transfer from Ce3+ to Yb3+ ions. The high quantum efficiency of the films implies that Ce3+,Yb3+ co-doped Y3A15O12 films have potential application by tuning the solar spectrum to enhance the efficiency of silicon solar cells.展开更多
Entangled photon pairs are crucial resources for quantum information processing protocols.Via the process of spontaneous parametric downconversion(SPDC),we can generate these photon pairs using bulk nonlinear crystals...Entangled photon pairs are crucial resources for quantum information processing protocols.Via the process of spontaneous parametric downconversion(SPDC),we can generate these photon pairs using bulk nonlinear crystals.Traditionally,the crystal is designed to satisfy a specific type of phase-matching condition.Here,we report controllable transitions among different types of phase matching in a single periodically poled potassium titanyl phosphate crystal.By carefully selecting pump conditions,we can satisfy different phase-matching conditions.This allows us to observe first-order Type-II,fifth-order Type-I,third-order Type-0,and fifth-order Type-II SPDCs.The temperature-dependent spectra of our source were also analyzed in detail.Finally,we discussed the possibility of observing more than nine SPDCs in this crystal.Our work not only deepens the understanding of the physics behind phase-matching conditions,but also offers the potential for a highly versatile entangled biphoton source for quantum information research.展开更多
Reliable generation of single photons is of key importance for fundamental physical experiments and quantum protocols.The periodically poled lithium niobate[LN]waveguide has shown promise for an integrated quantum sou...Reliable generation of single photons is of key importance for fundamental physical experiments and quantum protocols.The periodically poled lithium niobate[LN]waveguide has shown promise for an integrated quantum source due to its large spectral tunability and high efficiency,benefiting from the quasi-phase-matching.Here we demonstrate photon-pair sources based on an LN waveguide periodically poled by a tightly focused femtosecond laser beam.The pair coincidence rate reaches~8000 counts per second for average pump power of 3.2 m W[peak power is 2.9 k W).Our results prove the possibility of application of the nonlinear photonics structure fabricated by femtosecond laser to the integrated quantum source.This method can be extended to three-dimensional domain structures,which provide a potential platform for steering the spatial degree of freedom of the entangled two-photon states.展开更多
The two-photon state with spatial entanglement is an essential resource for testing fundamental laws of quantum mechanics and various quantum applications.Its creation typically relies on spontaneous parametric downco...The two-photon state with spatial entanglement is an essential resource for testing fundamental laws of quantum mechanics and various quantum applications.Its creation typically relies on spontaneous parametric downconversion in bulky nonlinear crystals where the tunability of spatial entanglement is limited.Here,we predict that ultrathin nonlinear lithium niobate metasurfaces can generate and diversely tune spatially entangled photon pairs.The spatial properties of photons including the emission pattern,rate,and degree of spatial entanglement are analyzed theoretically with the coupled mode theory and Schmidt decomposition method.We show that by leveraging the strong angular dispersion of the metasurface,the degree of spatial entanglement quantified by the Schmidt number can be decreased or increased by changing the pump laser wavelength and a Gaussian beam size.This flexibility can facilitate diverse quantum applications of entangled photon states generated from nonlinear metasurfaces.展开更多
Present-day advanced technologies heavily rely on the exciting magnetic and spectroscopic properties of lanthanide ions. In particular, their ability to generate well-characterized and intense near-infrared (NIR) lumi...Present-day advanced technologies heavily rely on the exciting magnetic and spectroscopic properties of lanthanide ions. In particular, their ability to generate well-characterized and intense near-infrared (NIR) luminescence is exploited in any modern fiber-optic telecommunication network. In this feature article, we first summarize the whereabouts underlying the design of highly luminescent NIR molecular edifices and materials. We then focus on describing the main trends in three applications related to this spectral range: telecommunications, biosciences, and solar energy conversion. In telecommunications, efforts concentrate presently on getting easily processable polymer-based waveguide amplifiers. Upconversion nanophosphors emitting in the visible after NIR excitation are now ubiquitous in many bioanalyses while their application to bio-imaging is still in its early stages; however, highly sensitive NIR-NIR systems start to be at hand for both in vitro and in vivo imaging, as well as dual probes combining magnetic resonance and optical imaging. Finally, both silicon-based and dye-sensitized solar cells benefit from the downconversion and upconversion capabilities of lanthanide ions to harvest UV and NIR solar light and to boost the overall quantum efficiency of these next-generation devices.展开更多
Ce3+ and Yb3+ co-activated GdBO3 phosphors were prepared by a conventional solid-state reaction method. X-ray powder diffraction, photoluminescent spectra and decay curves were used to characterize their structural ...Ce3+ and Yb3+ co-activated GdBO3 phosphors were prepared by a conventional solid-state reaction method. X-ray powder diffraction, photoluminescent spectra and decay curves were used to characterize their structural and luminescent properties. An efficient near-infrared (NIR) quantum cutting (QC) from the phosphors was observed, which involved the emission of two low-energy NIR photons (around 971 nm) from an absorbed ultra-violet (UV) photon at 358 nm via a cooperative energy transfer (CET) from Ce3+ to Yb3+ ions. The theoretical quantum efficiency was calculated and the maximum efficiency approached up to 164% before reaching the critical concentration quenching threshold. Our results demonstrated that these phosphors might find potential application in improving the efficiency of silicon based solar cells.展开更多
Conventional photoluminescence(PL)yields at most one emitted photon for each absorption event.Downconversion(or quantum cutting)materials can yield more than one photon by virtue of energy transfer processes between l...Conventional photoluminescence(PL)yields at most one emitted photon for each absorption event.Downconversion(or quantum cutting)materials can yield more than one photon by virtue of energy transfer processes between luminescent centers.In this work,we introduce Gd2O2S:Tm^(3+) as a multi-photon quantum cutter.It can convert near-infrared,visible,or ultraviolet photons into two,three,or four infrared photons of,1800 nm,respectively.The cross-relaxation steps between Tm^(3+) ions that lead to quantum cutting are identified from(time-resolved)PL as a function of the Tm^(3+) concentration in the crystal.A model is presented that reproduces the way in which the Tm^(3+) concentration affects both the relative intensities of the various emission lines and the excited state dynamics and providing insight in the quantum cutting efficiency.Finally,we discuss the potential application of Gd2O2S:Tm^(3+) for spectral conversion to improve the efficiency of next-generation photovoltaics.展开更多
BaMgAl10Ol7:Eu^2+,Yb^3+ was investigated as a possible quantum cutting system to enhance solar cells efficiency. Phosphors were synthesized by combustion method and composed of nanorods. Photoluminescence spectra s...BaMgAl10Ol7:Eu^2+,Yb^3+ was investigated as a possible quantum cutting system to enhance solar cells efficiency. Phosphors were synthesized by combustion method and composed of nanorods. Photoluminescence spectra showed that Eu in the sample was reduced to bivalence while Yb remained trivalence. Through a cooperative energy transfer process, the obtained powders exhibited both blue emission of Eu^2+ (around 450 nm) and near infrared emission of Yb^3+ (around 1020 nm) under broad band excitation (250-410 nm) originating from 4f→5d transition of Eu2+. Energy transfer phenomenon between the sensitizer Eu2+ and the activator Yb3+ was investigated via the luminescent spectra and the decay curves of Eu2+ with different Yb3+ concentrations. Results indicated that energy transfer efficiency from Eu2+ to Yb3+ was not high. The poor efficiency can be explained by the long distance between rare earth ions.展开更多
Fluorescence imaging in the second near-infrared region(900―1700 nm, NIR-II) with a high resolution and penetration depth due to the significantly reduced tissue scattering and autofluorescence has emerged as a usefu...Fluorescence imaging in the second near-infrared region(900―1700 nm, NIR-II) with a high resolution and penetration depth due to the significantly reduced tissue scattering and autofluorescence has emerged as a useful tool in biomedical fields. Recently, many efforts have been devoted to the development of fluorophores with an emission band covering the long-wavelength end of NIR-II region(1500―1700 nm) to eliminate the autofluorescence. Alternatively, we believe imaging with a narrow bandwidth could also reduce the autofluorescence. As a proof of concept, NaYF4:Yb,Nd@NaYF4 downconversion nanoparticles(DCNPs) with sharp NIR-II emission were synthesized. The luminescence of DCNPs showed a half-peak width of 49 nm centered at 998 nm, which was perfectly matched with a (1000±25) nm bandpass filter. With this filter, we were able to retain most of the emissions from the nanoparticles, while the autofluorescence was largely reduced. After PEGylation, the DCNPs exhibited great performance for blood vessel and tumor imaging in living mice with significantly reduced autofluorescence and interference signals. This work provided an alternative way for the low-autofluorescence imaging and emphasized the importance of narrow emitting rare-earth doped nanoparticles for NIR-II imaging.展开更多
基金supported by the National Nature Science Foundation of China (Grant No. 10774140)the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KJCX2-YW-M11)+1 种基金the Specialized Research Fund for the Doctoral Program of Higher Education,China (Grant No. 20060358054)the Special Foundation for Talents of Anhui Province,China (GrantNo. 2007Z021)
文摘Bi3+ and Yb3+ codoped cubic Y2O3 phosphors are prepared by pechini sol-gel method. Strong near-infrared (NIR) emission around 980 nm from Yb3+ (2F5/2+2 F7/2) is observed under ultraviolet light excitation. A broad excitation band ranging from 320 to 360 nm, owing to the 6s2→6s6p transition of Bi3+ ions, is recorded when the Yb3+ emission is monitored, which suggests a very efficient energy transfer from Bi3+ ions to Yb3+ ions. The Yb3+ concentration dependences of both the Bi3+ and the Yb3+ emissions are investigated. The decay curve of Bi3+ emission under the excitation of 355 nm pulse laser is used to explore the Bi3+ →+Yb3+ energy transfer process. Cooperative energy transfer (CET) is discussed as a possible mechanism for the near-infrared emission.
基金Project supported by the National Natural Science Foundation of China (Grant No. 20976002)the Beijing Natural Science Foundation, China (Grant No. 2122012)the Special Funding of the Ministry of Education of Guangdong Province, China (Grant No. 2011B090400100)
文摘A novel near-infrared (NIR) downconversion (DC) phosphor KSrPO4:Eu2+, Pr3+ is synthesized by the conventional high temperature solid-state reaction. The Eu2+ acts as an efficient sensitizer for Pr3+ in the KSrPO4 host. With broad- band near-ultraviolet light excitation induced by the 4f→5d transition of Eu2+, the characteristic NIR emission of Pr3+, peaking at 974 nm and 1019 nm due to 3po →1G4 and 1G4→3H4 transitions, is generated as a result of the energy transfer from Eu2+ to Pr3+. The luminescence spectra in both the visible and the NIR regions and the decay lifetime curves of Eu2+ prove the energy transfer from Eu2+ to Pr3+. This Eu2+ and Pr3+ co-doped KSrPO4 phosphor may be a promising candidate to modify the spectral mismatch behavior of crystalline solar cells and sunlight.
文摘The wide-band digital receiving systems require digital downconversion(DDC) with high data rate and short tuning time in order to intercept the narrow-band signals within broad tuning bandwidth. But these requirements can not be met by the commercial DDC. In this paper an efficient implementation architecture is presented. It combines the flexibility of DFT tuning with the efficiency of the polyphase filter bank decomposition. By first decimating the data prior to filtering and mixing, this architecture gives a better solution to the mismatch between the lower hardware speed and high data rate. The computer simulations show the feasibility of this processing architecture.
基金supported in part by the National Key Research and Development Program of China(No.2018YFB2201702)the National Natural Science Foundation of China(Nos.U21A20507 and 62005228)the Fundamental Research Funds for the Central Universities(No.2682021CX050)。
文摘We experimentally demonstrated the use of intelligent impairment equalization(IIE)for microwave downconversion link linearization in noncooperative systems.Such an equalizer is realized based on an artificial neural network(ANN).Once the training process is completed,the inverse link transfer function can be determined.With the inverse transformation for the detected signal after transmission,the third-order intermodulation distortion components are suppressed significantly without requiring any prior information from an input RF signal.Furthermore,fast training speed is achieved,since the configuration of ANN-based equalizer is simple.Experimental results show that the spurious-free dynamic range of the proposed link is improved to 106.5 dB·Hz^(2/3),which is 11.3 dB higher than that of a link without IIE.Meanwhile,the training epochs reduce to only five,which has the potential to meet the practical engineering requirement.
基金Project supported by the National Natural Science Foundation of China (10774140,11074245,11011120083)Knowledge Innovation Project of the Chinese Academy of Sciences (KJCX2-YW-M11)Special Foundation for Talents of Anhui Province,China (2007Z021)
文摘All of the samples were synthesized by sol-gel methods.Two approaches to charge compensation,(i) 2Ca2+→Yb3++M+,where M+ is an alkali ion like Li+,Na+ and K+,and(ii) indirect charge compensation:3Ca2+→2Yb3++vacancy,were studied in detail.It was found that charge compensation would be very beneficial for the growth of the grains,especially in Li+ ions added samples.All the grains were homogeneously spherical with less boundaries;in addition,a great variety of the absorption ability in different charge compensation samples were observed:in comparison with the phosphors without charge compensation,indirectly charge compensated and Li+ ions added phosphors showed much stronger absorption strength in the ultraviolet(UV) region whereas that of Na+ and K+ ions added samples was much weaker;moreover,measurements of the emission intensities showed that:in comparison with the phosphors without charge compensation,the visible emission intensity from MoO42-decreased a lot in indirectly charge compensated and Li+ ions added phosphors,whereas there was a remarkable increase of the near infrared(NIR) emission intensity from Yb3+ ions in the two types of samples under 266 nm excitation,implying more efficient energy transfer(ET) from MoO42-to Yb3+ ions;at last,measurements and analysis of the decay curves of the visible 495 nm emission were carried out,and it was found that the energy transfer from MoO42-to Yb3+ ions were more efficient in the two above types of phosphors.The theoretical quantum cutting(QC) efficiency was also improved greatly.Overall,the addition of Li+ ions would be very beneficial for the morphology of the powders in addition to the growth of the grains.It was advantageous to increase the downconversion(DC) quantum efficiency;however,indirect charge compensation would enhance the NIR emission intensity to the most for its strongest absorption ability in the UV region.
基金Project supported by National Natural Science Foundation of China (10774140, 11047147, 11074245, 11011120083)Knowledge Innovation Project of The Chinese Academy of Sciences (KJCX2-YW-M11)the Natural Science Foundation of Chongqing Municipal Education Commission (KJTD201016, KJ090514)
文摘Tb3+ and Yb3+ codoped Lu2O3 nanophosphors were synthesized by the reverse-strike co-precipitation method. The obtained Lu2O3:Tb3+,Yb3+ nanophosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra. The XRD results showed that all the prepared nanophosphors could be readily indexed to pure cubic phase of Lu2O3 and indicated good crystallinity. The Tb3+→Yb3+ energy transfer mechanisms in the UV-blue region in Lu2O3 nanophosphors were investigated. The experimental results showed that the strong visible emission around 543 nm from Tb3+ (5D4→7F5) and near-infrared (NIR) emission around 973 nm from Yb3+ (2F5/2→2F7/2) of Lu2O3:Tb3+,Yb3+ nanophosphors were observed under ultraviolet light excitation, respectively. Tb3+ could be effectively excited up to its 4f75d1 state and relaxed down to the 5D4 level, from which the energy was transferred cooperatively to two neighboring Yb3+. The Yb3+ concentration dependent luminescent properties and lifetimes of both the visible and NIR emissions were also studied. The lifetime of the visible emission decreased with the increase of Yb3+ concentration, verifying the efficient energy transfer from the Tb3+ to the Yb3+. Cooperative energy transfer (CET) from Tb3+ to Yb3+ was discussed as a possible mechanism for the near-infrared emission. When doped concentrations were 1 mol.% Tb3+ and 2 mol.% Yb3+, the intensity of NIR emission was the strongest.
基金Project supported by the National Key Basic Research Program of China (2013CB921800)the National Natural Science Foundation of China (11074245, 11204292, 11274299)the Fundamental Research Funds for the Central Universities (WK2030020022)
文摘An efficient near-infrared (NIR) downconversion (DC) by converting broadband ultraviolet (UV) into NIR was demon- strated in YVO4:Tma+,yb3+ phosphors. The phosphors were extensively characterized using various methods such as X-ray diffrac- tion, photoluminescence excitation, photoluminescence spectra and decay lifetime to provide supporting evidence for DC process. Upon UV light varying from 260 to 350 nm or blue light (473 nm) excitation, an intense NIR emission of Yb3+ corresponding to tran- sition of 2Fs/2/5→2F7/2 peaking at 985 nm was generated. The visible emission, the NIR mission and the decay lifetime of the phosphors of various Yb3+ concentrations were investigated. Experimental results showed that the energy transfer from vanadate group to Yb3+ via Tm3+ was very efficient. Application of the broadband DC YVO4:Tma+,yb3+ phosphors might greatly enhance response of sili- con-based solar cells.
文摘Exploiting microwave photonic(MWP)techniques to generate and distribute high-frequency millimeter-wave(mm-wave)signals,termed mm-wave radio over fiber(m-RoF)signals,holds considerable potential for achieving highdensity and high-capacity fifth-generation and beyond networks.Herein,we experimentally validate a broadband m-RoF uplink fronthaul transmission system using the MWP downconversion concept,which comprises receiving and processing radio-frequency(RF)signals in the unlicensed V-band at around 60 GHz.The proposed system harnesses the simple cascaded modulator topology,in which an ultrawideband off-the-shelf Mach–Zehnder modulator(MZM)renders a simplestructured remote radio head by directly encoding the broadband 60 GHz uplink RF signal into the optical carrier.The nonlinear transfer function of another MZM at the center unit is explored to achieve subharmonic downconversion using cost-effective low-frequency local oscillator signals.Based on proof-of-concept experiments,mm-wave four quadrature amplitude modulation orthogonal frequency-division multiplexing signals centered at frequencies ranging from 51 GHz to 70 GHz are successfully downconverted into signals at the intermediate frequency(IF)of 1.4 GHz.In the case of 1.2 m mm-wave,free-space,and 5 km m-RoF transmissions,the obtained IF signals with a total bandwidth of 2.4 GHz achieve a bit-to-error ratio performance lower than the 7%hard-decision forward error correction limit of 3.8×10^(−3).A gross bit rate of 10 Gbit/s can be achieved over a total spectrum of up to 10 GHz,which fully covers the globally unlicensed V-band of 57-66 GHz.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50672087 and 60778039, the National Basic Research Programme of China under Grant No 2006CB806007, the National High-Tech Research and Development Programme of China under Grant No 2006AA03Z304, and the Programme for Changjiang Scholars and Innovative Research Team in University (IRT0651).
文摘We report on cooperative quantum cutting in Tb^3+- Yb^3+ codoped glass ceramics. Precipitation of BaF2 nanocrystals is confirmed by XRD and HRTEM analysis. Near-infrared emission due to transition of Yb^3+ ions under 485 nm excitation indicates cooperative energy transfer from Tb^3+ to Yb^3+. The quantum efficiency of this process reaches 145%. The realization of quantum cutting in glass ceramics may have promising applications in solar cells.
基金Funded by the China Postdoctoral Science Foundation(No.2012M511801)the National Natural Science Foundation of China(Nos.11474104 and 51372092)
文摘Ce3+, Yb3+ co-doped Y3Al5O12 films were prepared by pulse laser deposition. X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectra were used to characterize their structural and luminescent properties. Near-infrared quantum cutting from the films was observed via a cooperative energy transfer from Ce3+ to Yb3+ ions. The high quantum efficiency of the films implies that Ce3+,Yb3+ co-doped Y3A15O12 films have potential application by tuning the solar spectrum to enhance the efficiency of silicon solar cells.
基金supported by the National Natural Science Foundation of China(Nos.12074299,11704290,and 92365106)the Guangdong Provincial Key Laboratory(No.GKLQSE202102)the Natural Science Foundation of Hubei Province(2022CFA039)。
文摘Entangled photon pairs are crucial resources for quantum information processing protocols.Via the process of spontaneous parametric downconversion(SPDC),we can generate these photon pairs using bulk nonlinear crystals.Traditionally,the crystal is designed to satisfy a specific type of phase-matching condition.Here,we report controllable transitions among different types of phase matching in a single periodically poled potassium titanyl phosphate crystal.By carefully selecting pump conditions,we can satisfy different phase-matching conditions.This allows us to observe first-order Type-II,fifth-order Type-I,third-order Type-0,and fifth-order Type-II SPDCs.The temperature-dependent spectra of our source were also analyzed in detail.Finally,we discussed the possibility of observing more than nine SPDCs in this crystal.Our work not only deepens the understanding of the physics behind phase-matching conditions,but also offers the potential for a highly versatile entangled biphoton source for quantum information research.
基金supported financially by the National Key R&D Program of China(Nos.2019YFA0705000,2017YFA0303800,2017YFA0303700,2019YFA0308700,and 2020YFA0309500)the National Natural Science Foundation of China(Nos.12074197,12074196,11774183,and 11922406)。
文摘Reliable generation of single photons is of key importance for fundamental physical experiments and quantum protocols.The periodically poled lithium niobate[LN]waveguide has shown promise for an integrated quantum source due to its large spectral tunability and high efficiency,benefiting from the quasi-phase-matching.Here we demonstrate photon-pair sources based on an LN waveguide periodically poled by a tightly focused femtosecond laser beam.The pair coincidence rate reaches~8000 counts per second for average pump power of 3.2 m W[peak power is 2.9 k W).Our results prove the possibility of application of the nonlinear photonics structure fabricated by femtosecond laser to the integrated quantum source.This method can be extended to three-dimensional domain structures,which provide a potential platform for steering the spatial degree of freedom of the entangled two-photon states.
基金supported by the Australian Research Council(DP190101559,CE200100010).
文摘The two-photon state with spatial entanglement is an essential resource for testing fundamental laws of quantum mechanics and various quantum applications.Its creation typically relies on spontaneous parametric downconversion in bulky nonlinear crystals where the tunability of spatial entanglement is limited.Here,we predict that ultrathin nonlinear lithium niobate metasurfaces can generate and diversely tune spatially entangled photon pairs.The spatial properties of photons including the emission pattern,rate,and degree of spatial entanglement are analyzed theoretically with the coupled mode theory and Schmidt decomposition method.We show that by leveraging the strong angular dispersion of the metasurface,the degree of spatial entanglement quantified by the Schmidt number can be decreased or increased by changing the pump laser wavelength and a Gaussian beam size.This flexibility can facilitate diverse quantum applications of entangled photon states generated from nonlinear metasurfaces.
基金Project supported through grants from the Swiss National Science Foundationthe WCU program from the National Science Foundation of Korea for grant R31-10035
文摘Present-day advanced technologies heavily rely on the exciting magnetic and spectroscopic properties of lanthanide ions. In particular, their ability to generate well-characterized and intense near-infrared (NIR) luminescence is exploited in any modern fiber-optic telecommunication network. In this feature article, we first summarize the whereabouts underlying the design of highly luminescent NIR molecular edifices and materials. We then focus on describing the main trends in three applications related to this spectral range: telecommunications, biosciences, and solar energy conversion. In telecommunications, efforts concentrate presently on getting easily processable polymer-based waveguide amplifiers. Upconversion nanophosphors emitting in the visible after NIR excitation are now ubiquitous in many bioanalyses while their application to bio-imaging is still in its early stages; however, highly sensitive NIR-NIR systems start to be at hand for both in vitro and in vivo imaging, as well as dual probes combining magnetic resonance and optical imaging. Finally, both silicon-based and dye-sensitized solar cells benefit from the downconversion and upconversion capabilities of lanthanide ions to harvest UV and NIR solar light and to boost the overall quantum efficiency of these next-generation devices.
基金Project supported by the National Natural Science Foundation of China (10904131)Student Scientific Activities Programme (Emerging Artists Talents Scheme) of Zhejiang Province (2010R404067)
文摘Ce3+ and Yb3+ co-activated GdBO3 phosphors were prepared by a conventional solid-state reaction method. X-ray powder diffraction, photoluminescent spectra and decay curves were used to characterize their structural and luminescent properties. An efficient near-infrared (NIR) quantum cutting (QC) from the phosphors was observed, which involved the emission of two low-energy NIR photons (around 971 nm) from an absorbed ultra-violet (UV) photon at 358 nm via a cooperative energy transfer (CET) from Ce3+ to Yb3+ ions. The theoretical quantum efficiency was calculated and the maximum efficiency approached up to 164% before reaching the critical concentration quenching threshold. Our results demonstrated that these phosphors might find potential application in improving the efficiency of silicon based solar cells.
基金Financial support from the National Science Foundation of China(51125005 and 51472088)is gratefully acknowledgedDechao Yu thanks the China Scholarship Council(CSC,File No.201206150022)for a scholarshipThis work is part of the research program of the‘Stichting voor Fundamenteel Onderzoek der Materie(FOM)’,which is financially supported by the‘Nederlandse Organisatie voor Wetenschappelijk Onderzoek(NWO)’.
文摘Conventional photoluminescence(PL)yields at most one emitted photon for each absorption event.Downconversion(or quantum cutting)materials can yield more than one photon by virtue of energy transfer processes between luminescent centers.In this work,we introduce Gd2O2S:Tm^(3+) as a multi-photon quantum cutter.It can convert near-infrared,visible,or ultraviolet photons into two,three,or four infrared photons of,1800 nm,respectively.The cross-relaxation steps between Tm^(3+) ions that lead to quantum cutting are identified from(time-resolved)PL as a function of the Tm^(3+) concentration in the crystal.A model is presented that reproduces the way in which the Tm^(3+) concentration affects both the relative intensities of the various emission lines and the excited state dynamics and providing insight in the quantum cutting efficiency.Finally,we discuss the potential application of Gd2O2S:Tm^(3+) for spectral conversion to improve the efficiency of next-generation photovoltaics.
基金Project supported by National Natural Science Foundation of China (11074245, 11074315, 11204292, 11174005)the Fundamental Research Funds for the Central Universities (2340000034)the Funding of Creative Youth by University of Science &Technology of China
文摘BaMgAl10Ol7:Eu^2+,Yb^3+ was investigated as a possible quantum cutting system to enhance solar cells efficiency. Phosphors were synthesized by combustion method and composed of nanorods. Photoluminescence spectra showed that Eu in the sample was reduced to bivalence while Yb remained trivalence. Through a cooperative energy transfer process, the obtained powders exhibited both blue emission of Eu^2+ (around 450 nm) and near infrared emission of Yb^3+ (around 1020 nm) under broad band excitation (250-410 nm) originating from 4f→5d transition of Eu2+. Energy transfer phenomenon between the sensitizer Eu2+ and the activator Yb3+ was investigated via the luminescent spectra and the decay curves of Eu2+ with different Yb3+ concentrations. Results indicated that energy transfer efficiency from Eu2+ to Yb3+ was not high. The poor efficiency can be explained by the long distance between rare earth ions.
基金This work was supported by the National Natural Science Foundation of China(Nos.21975131,21674048)the Fund of Synergetic Innovation Center for Organic Electronics and Information Displaysthe Primary Research&Development Plan of Jiangsu Province,China(No.BE2016770).
文摘Fluorescence imaging in the second near-infrared region(900―1700 nm, NIR-II) with a high resolution and penetration depth due to the significantly reduced tissue scattering and autofluorescence has emerged as a useful tool in biomedical fields. Recently, many efforts have been devoted to the development of fluorophores with an emission band covering the long-wavelength end of NIR-II region(1500―1700 nm) to eliminate the autofluorescence. Alternatively, we believe imaging with a narrow bandwidth could also reduce the autofluorescence. As a proof of concept, NaYF4:Yb,Nd@NaYF4 downconversion nanoparticles(DCNPs) with sharp NIR-II emission were synthesized. The luminescence of DCNPs showed a half-peak width of 49 nm centered at 998 nm, which was perfectly matched with a (1000±25) nm bandpass filter. With this filter, we were able to retain most of the emissions from the nanoparticles, while the autofluorescence was largely reduced. After PEGylation, the DCNPs exhibited great performance for blood vessel and tumor imaging in living mice with significantly reduced autofluorescence and interference signals. This work provided an alternative way for the low-autofluorescence imaging and emphasized the importance of narrow emitting rare-earth doped nanoparticles for NIR-II imaging.