Up-conversion photoluminescence characteristics of Yb^(3+):Er^(3+):Tm^(3+) co-doped borosilicate glasses

Yb^3＋：Er^3＋：Tm^3＋co-doped borosilicate glasses are prepared. Their strong up-conversion photoluminescence spectra in a range from ultra-violet to near-infrared, which are excited by a 978-nm laser diode, are measured, and the mechanisms of energy transfer among Yb^3＋ Er^3＋ and Tm^3＋ ions are discussed. The results show that there is an unexpected wavelength at 900-nm emission from Yb^3＋ Stark splitting levels to pump Tm^3＋ ions and there exists an optimum pump power. The concentration of the Tm^3＋ dopant gives rise to a prominent effect on the intensity of visible and near-infrared emissions for the yb^3＋：Er^3＋：Tm^3＋ co-doped borosilicate glasses.

Efficient up-conversion photoluminescence in all-inorganic lead halide perovskite nanocrystals

Up-conversion photoluminescence(UCPL)refers to the elementary process where low-energy photons are converted into high-energy ones via consecutive interactions inside a medium.When additional energy is provided by intermnal thermal energy in the form of lttice vibrations(phonons),the process is called phonon-assisted UCPL.Here,we report the exceptionally large phonon-assisted energy gain of up to^8kgT(kg is Boltzmann constant,T is temperature)on all-inorganic lead halide perovskite semiconductor colloidal nanocrystals that goes beyond the maximum capabilty of only harvesting optical phonon modes.By systematic optical study in combination with a statistical probability model,we explained the nontrivial phonon-assisted UCPL process in perovskites nanocrystals,where in addition to the strong electron-phonon(light-matter)coupling,other nonlinear processes such as phonon-phonon(matter-matter)interaction also effectively boost the up-conversion efficiency.

Effects of the annealing temperature on the structure and up-conversion photoluminescence of ZnO film

The up-conversion film is being tried to increase the photoelectric conversion efficiency of the silicon solar cell. To improve the efficiency of the photoluminescence film, the effects of the annealing temperature were investigated on the structure and photoluminescence of the ZnO up-conversion film, which was prepared using the sol-gel method and the spin-coating technique. The results show that the organic compounds and water in the ZnO film were completely eliminated when the annealing temperature reached 500 ℃. The crystallinity of film is improved and the average grain size continuously increases as increasing the annealing temperature. The transmittance in the wavelength range of 400-2000 nm continuously increases as the annealing temperature increases from 500 ℃ to 700 0 C, whilst it decreases first and then increases as the annealing temperature increases from 800 ℃ to 1000℃. When the film is excited with a laser of 980 nm, there are two intense emission bands in the up-conversion emission spectra, 542-nm green light and 660-nm red light, corresponding to Ho;:;S;/;F;→;I;and;F;→;I;transitions, respectively. In addition, the intensity of up-conversion luminescence for the film increases first and then decreases with the increase of the annealing temperature. When the annealing temperature is at 900 ℃, the film consists of small round compact particles with a high degree of crystallization,reaching maximum up-conversion intensity of the film.

Up-conversion photoluminescence emissions of CaMoO4：Pr3＋/Yb3＋ powder

CaMoO_4：Pr^（3＋）/Yb^（3＋） powder was successfully synthesized by a facile hydrothermal method. X-ray diffraction（XRD） patterns of samples confirmed tetragonal structure and morphology and sizes were confirmed by scanning electron microscopy（SEM） analyses. Particles consisted of regular micro-spheres with uniform sizes, the diameter of each sphere lay in the range of 3 to 4 μm. The up-conversion photoluminescence emission and its concentration dependence were investigated under infrared excitation at 980 nm. All the UC micro-particles exhibited the typical blue, green and red emissions. Dominant blue emissions originated from ~3P_0→~3H_4 and intense red emissions originated from ~3P0→~3F_2 transitions, and they both belonged to two-photon excitation processes in CaMoO_4： Yb^（3＋）/Pr^（3＋） powder. The optimum doping concentrations of Pr^（3＋） and Yb^（3＋） for the highest UC luminescence were 0.1 mol.% and 16 mol.%, respectively. The possible up-conversion mechanisms were discussed in detail. It was found that the UC emission could be well controlled from blue to green to white color by adjusting the concentration of Pr^（3＋） ions in CaMoO_4：Pr^（3＋）/Yb^（3＋） microcrystal. So it is a candidate material for solid-state lasers, biological imaging, solar cells, and optical communications.

Intensive up-conversion photoluminescence of Er^(3+)-doped Bi_(7)Ti_(4)NbO_(21)ferroelectric ceramics and its temperature sensing

The intensive up-conversion(UC)photoluminescence and temperature sensing behavior of Er3t-doped Bi_(7)Ti_(4)NbO_(21)(BTN)ferroelectric ceramics prepared by a conventional solid-state reaction technique have been investigated.The X-ray diffraction and field emission scanning electron microscope analyses demonstrated that the Er3t-doped BTN ceramics are single phase and uniform flake-like structure.With the Er3t ions doping,the intensive UC emission was observed without obviously changing the properties of ferroelectric.The optimal emission intensity was obtained when Er doping level was 15 mol.%.The temperature sensing behavior was studied by fluorescence intensity ratio(FIR)technique of two green UC emission bands,and the experimental data fitted very well with the function of temperature in a range of 133–573 K.It suggested that the Er3t-doped BTN ferroelectric ceramics are very good candidates for applications such as optical thermometry,electro-optical devices and bio-imaging ceramics.

Assembly of functional carboxymethyl cellulose/polyethylene oxide/anatase TiO_(2) nanocomposites and tuning the dielectric relaxation, optical, and photoluminescence performances

Nanocomposite films consisting of carboxymethyl cellulose,polyethylene oxide(CMC/PEO),and anatase titanium diox-ide(TO)were produced by the use of sol-gel and solution casting techniques.TiO2 nanocrystals were effectively incorporated into CMC/PEO polymers,as shown by X-ray diffraction(XRD)and attenuated total reflectance fourier transform infrared(ATR-FTIR)analysis.The roughness growth is at high levels of TO nanocrystals(TO NCs),which means increasing active sites and defects in CMC/PEO.In differential scanning calorimetry(DSC)thermograms,the change in glass transition temperature(Tg)val-ues verifies that the polymer blend interacts with TO NCs.The increment proportions of TO NCs have a notable impact on the dielectric performances of the nanocomposites,as observed.The electrical properties of the CMC/PEO/TO nanocomposite undergo significant changes.The nanocomposite films exhibit a red alteration in the absorption edge as the concentration of TO NCs increases in the polymer blend.The decline in the energy gap is readily apparent as the weight percentage of TO NCs increases.The photoluminescence(PL)emission spectra indicate that the sites of the luminescence peak maximums show slight variation;peaks get wider,while their intensities decrease dramatically as the concentration of TO increases.These nanocomposite materials show potential for multifunctional applications including optoelectronics,antireflection coatings,pho-tocatalysis,light emitting diodes,and solid polymer electrolytes.

Transition metal coordination polymers with flexible dicarboxylate ligand:Synthesis,characterization,and photoluminescence property

Under solvothermal conditions,six new coordination polymers(CPs)[Mn(L)(phen)(H_(2)O)]_(n)(1),[Co(L)(phen)(H_(2)O)]_(n)(2),[Cu(L)(phen)(H_(2)O)]_(n)(3),[Zn_(2)(L)_(2)(phen)2(H_(2)O)]_(n)(4),[Zn(L)(phen)]_(n)(5),and[Cd(L)(phen)2]_(n)(6)were synthesized by reactions of dicarboxylate ligand 2,2'-(1,2-phenylenebis(methylene))bis(sulfanediyl)dinobutyric acid(H_(2)L)and 1,10-phenanthroline(phen)with the corresponding metal salts.Complexes 1-6 have been structurally characterized by single-crystal X-ray diffraction analyses,elemental analysis,IR,thermogravimetric analysis,and powder X-ray diffraction.The structures of 1-6 are 1D chains,which are further connected by hydrogen bonding interac-tions to form 3D supramolecular structures.Among them,1 and 2 are isomorphic with L2-of syn-conformation,while L2-shows anti-conformation in 3-6.In addition,the solid-state photoluminescence property of 4-6 was investigated.

Upconversion photoluminescence of Er-doped Bi_(4)Ti_(3)O_(12) ceramics enhanced by vacancy clusters revealed by positron annihilation spectroscopy

Doping of rare earth elements into Bi_(4)Ti_(3)O_(12)can significantly enhance the upconversion photoluminescence(UCPL)properties,but its structure-property relationship is still unclear.In this work,Er-doped bismuth titanate Bi_(4-x)Er_(x)Ti_(3)O_(12)(x=0,0.1,0.2,0.3,0.4,0.5)ceramics were synthesized via solid-state reaction method.The x-ray diffraction analysis confirmed the orthorhombic crystalline structure of the Bi4-xErxTi3012ceramics without any secondary phases.Experiments and calculations of positron annihilation spectroscopy were carried out to characterize their defect structure.The comparison between the experimental and calculated lifetime revealed that vacancy clusters were the main defects in the ceramics.The increase of the intensity of the second positron lifetime component(I_(2))of Bi_(3.5)Er_(0.5)Ti_(3)O_(12)ceramics indicated the presence of a high concentration of vacancy clusters.The UCPL spectra showed the sudden enhanced UCPL performance in Bi3.7Er0.3Ti3O12and Bi_(3.5)Er_(0.5)Ti_(3)O_(12)ceramics,which were consistent with the variation of the second positron lifetime component(I2).These results indicate that the enhanced UCPL properties are influenced not only by the concentrations of rare earth ions but also by the concentration of vacancy clusters present within the ceramics.

CO_(2)-Induced Modulation of Si-O Bonds for Low Temperature Plastic Deformation of Amorphous Silica Nanoparticles with Enhanced Photoluminescence

Modulation of Si-O bonds under mild conditions has been a challenging issue in the field of material science,which is critical to manufacture highperformance silica-based optical and photonic devices.Herein,we introduce a nondestructive technique to achieve Si-O bond rearrangement,leading to plastic deformation and photoluminescence enhancement of amorphous silica nanoparticles using supercritical carbon dioxides in EtOH/H_(2)O solution under mild temperature.Specifically,plastic deformation is achieved by treating hollow mesoporous silica nanospheres using supercritical CO_(2)at 40°C under 20 MPa.Experimental and theoretical studies revealed the critical role of supercritical CO_(2)in the plastic deformation process,which can be intercalated into the hollow mesoporous silica nanospheres with anisotropic stresses and induces the rearrangement of Si-O bonds and transformation of ring structures.This work suggests a novel approach to engineer high-performance nano-silica glass components for numerous optical and photonic devices under mild condition.

Unraveling the efficiency losses and improving methods in quantum dot-based infrared up-conversion photodetectors

Quantum dot-based up-conversion photodetector,in which an infrared photodiode(PD)and a quantum dot light-emitting diode(QLED)are back-to-back connected,is a promising candidate for low-cost infrared imaging.However,the huge efficiency losses caused by integrating the PD and QLED together hasn’t been studied sufficiently.This work revealed at least three origins for the efficiency losses.First,the PD unit and QLED unit usually didn’t work under optimal conditions at the same time.Second,the potential barriers and traps at the interconnection between PD and QLED units induced unfavorable carrier recombination.Third,much emitted visible light was lost due to the strong visible absorption in the PD unit.Based on the understandings on the loss mechanisms,the infrared up-conversion photodetectors were optimized and achieved a breakthrough photon-to-photon conversion efficiency of 6.9%.This study provided valuable guidance on how to optimize the way of integration for up-conversion photodetectors.

Energy Transfer and Photoluminescence Enhancement in WS_(2)/hBN/MoS_(2) Heterostructures

Two-dimensional(2D)transition metal dichalcogenides(TMDs)and their heterostructures(HSs)exhibit unique optical properties and show great promise for developing next-generation optoelectronics.However,the photo-luminescence(PL)quantum yield of monolayer(1L)TMDs is still quite low at room temperature,which severely lim-its their practical applications.Here we report a PL enhancement effect of 1L WS_(2) at room temperature when con-structing it into 1L-WS_(2)/hBN/1L-MoS_(2) vertical HSs.The PL enhancement factors(EFs)can be up to 4.2.By using transient absorption(TA)spectroscopy,we demonstrate that the PL enhancement effect is due to energy transfer from 1L MoS_(2) to 1L WS_(2).The energy transfer process occurs on a picosecond timescale and lasts more than one hundred picoseconds which indicates a prominent contribution from exciton-exciton annihilation.Furthermore,the PL en-hancement effect of 1L WS_(2) can be observed in 2L-MoS_(2)/hBN/1L-WS_(2) and 3L-MoS_(2)/hBN/1L-WS_(2) HSs.Our study provides a comprehensive understanding of the energy transfer process in the PL enhancement of 2D TMDs and a fea-sible way to optimize the performance of TMD-based optoelectronic devices.

Low-Temperature Growth and Photoluminescence of SnO_2 Nanowires

SnO2 nanowires with a diameter of 25nm are synthesized at 550~C by Au-Ag catalyst assisted thermal evapora- tion of SnO powders. The room-temperature photoluminescence spectra （PL） of the prepared nanowires are measured. Among the four PL peaks,the peak of 418nm is newly observed. This peak is caused by the plane defects of the twinned crystal nanowires. The formation of SnO2 nanowires at low temperature is pursued on the basis of the VLS mechanism and application of the reaction source of SnO. We suggest that the chemical reactions of the low temperature and low concen- tration of the vaporized species are responsible for the thinner size of the SnO2 nanowires.

Origin of Photoluminescence of Neodymium-Implanted Silicon

Neodymium is incorporated into single crystalline silicon on MEVVA (Metal Vapor Vacuum Arc) ion source.At room temperature,strong ultra violet and visible fluorescence are observed at the excitation wavelength of 220nm.Luminescence intensity increases with the increase of ion fluence.XPS results manifest that Si-O,Nd-O,Si-Si and O-O bonds exist in the implanted layers.Luminescence mainly results from the radiation transition in the intra 4f shell of Nd 3+ ion.The defects' and damages' contribution to the luminescence is also presented.

Morphology, photoluminescence and gas sensing of Ce-doped ZnO microspheres

Ce-doped ZnO microspheres were solvothermally prepared, and their microstructure, morphology, photoluminescence, and gas sensing were investigated by X-ray diffractometer, field emission scanning electron microscopy, transmission electron microscopy, fluorescence spectrometer and gas sensing analysis system. The results showed that the Ce-doped ZnO microspheres were composed of numerous nanorods with a diameter of 70 nm and a wurtzite structure. Ce-doping could cause a morphological transition from loose nanorods assembly to a tightly assembly in the microspheres. Compared with pure ZnO, the photoluminescence of the Ce-doped microspheres showed red-shifted UV emission and an enhanced blue emission. Particularly, the Ce-doped ZnO sensors exhibited much higher sensitivity and selectivity to ethanol than that of pure ZnO sensor at 320 °C. The ZnO microspheres doped with 6% Ce (mole fraction) exhibited the highest sensitivity (about 30) with rapid response (2 s) and recovery time (16 s) to 50×10?6 ethanol gas.

Synthesis and photoluminescence properties of single-crystal ZnO hexagonal pyramids by PEG400-assisted thermal decomposition route

Large-scale synthesis of ZnO hexagonal pyramids was achieved by a simple thermal decomposition route of precursor at 240 oC in the presence of PEG400. The precursor was obtained by room-temperature solid-state grinding reaction between Zn（CH3COO）2-2H2O and Na2CO3. Crystal structure and morphology of the products were analyzed and characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and high-resolution transmission electron microscopy （HRTEM）. The results of further experiments show that PEG400 has an important role in the formation of ZnO hexagonal pyramids. Difference between the single and double hexagonal pyramid structure may come from the special thermal decomposition reaction. The photoluminescence （PL） spectra of ZnO hexagonal pyramids exhibit strong near-band-edge emission at about 386 nm and weak green emission at about 550 nm. The Raman-active vibration at about 435 cm-1 suggests that the ZnO hexagonal pyramids have high crystallinity.

Time-resolved photoluminescence of anatase/rutile TiO_2 phase junction revealing charge separation dynamics

Junctions are an important structure that allows charge separation in solar cells and photocatalysts. Here, we studied the charge transfer at an anatase/rutile TiO2 phase junction using time-resolved photoluminescence spectroscopy. Visible （-S00 nm） and near-infrared （NIR, -830 nm） emissions were monitored to give insight into the photoinduced charges of anatase and rutile in the junction, respectively, New fast photoluminescence decay components appeared in the visible emission of futile-phase dominated TiO2 and in the NIR emission of many mixed phase TiO2samples. The fast decays confirmed that the charge separation occurred at the phase junction. The visible emission intensity from the mixed phase TiO2 increased, revealing that charge transfer from rutile to anatase was the main pathway. The charge separation slowed the microsecond time scale photolumines- cence decay rate for charge carriers in both anatase and rutile. However, the millisecond decay of the charge carriers in anatase TiO2 was accelerated, while there was almost no change in the charge carrier dynamics of rutile TiO2. Thus, charge separation at the anatase/rutile phase junction caused an increase in the charge carrier concentration on a microsecond time scale, because of slower electron-hole recombination. The enhanced photocatalytic activity previously observed at ana- tase/rutile phase junctions is likely caused by the improved charge carrier dynamics we report here. These findings may contribute to the development of improved photocatalytic materials.

Synthesis and Photoluminescence of Amorphous Silicon Oxycarbide Nanowires

Synthesis of amorphous SiCO nanowires was carried out by means of direct current are discharge. Free-standing SiCO nanowires were deposited on the surface of a graphite crucible without any catalyst and template. The SiCO nanowires were analyzed by XRD, SEM, TEM, XPS, and FTIR. The SiCO nanowires were typically 20-100 gm in length and 10-100 nm in diameter as measured by SEM and TEM. The XPS and FTIR spectroscopy analysis confirmed that the Si atoms share bonds with O and C atoms in mixed SiCO units. The PL spectrum of the SiCO nanowires showed strong and stable white emissions at 454 and 540 nm. A plasma-assisted vapor-solid growth mechanism is proposed to be responsible for the formation of the SiCO nanowires.

CMOS Quadrature Modulator and Up-Conversion Mixer for 802.11a Wireless LAN Systems

A quadrature modulator and an up-conversion mixer for an 802. lla wireless LAN system are designed and fabricated in 0.18μm gate length standard CMOS technology. A current feedback loop with a transconductor is used to improve the linearity of the quadrature modulator;An LC resonant tank is used as the load of the upconversion mixer to improve its gain and increase the voltage swing. The measurement results show that the input P1dB achieves -3.6dBm, the transducer power gain of the circuit is -3.6dB,and the current consumes about 45.8mA with a 1.8V power supply.

Resonant Raman Scattering and Photoluminescence Emissions from Above Bandgap Levels in Dilute GaAsN Alloys

The transitions of E0 ,E0 ＋A0, and E＋ in dilute GaAs（1-x） Nx alloys with x = 0.10% ,0.22% ,0.36% ,and 0.62% are observed by micro-photoluminescence. Resonant Raman scattering results further confirm that they are from the intrinsic emissions in the studied dilute GaAsN alloys rather than some localized exciton emissions in the GaAsN alloys. The results show that the nitrogen-induced E E＋ and E0 ＋ A0 transitions in GaAsN alloys intersect at a nitrogen content of about 0.16%. It is demonstrated that a small amount of isoelectronic doping combined with micro-photoluminescence allows direct observation of above band gap transitions that are not usually accessible in photoluminescence.

SELECTIVELY-EXCITED PHOTOLUMINESCENCE IN NC-Si:Er

Erbium （Er） doped in nanocrystalline Si （nc-Si：Er） surrounded by SiO2 is investigated by selectivelyexcited photoluminescence（PL） technique. Optical transitions come from nc-Si （peak located at 1.39 eV, denoted as Enc-Si） and Er ions （peak located at 0. 81 eV, denoted as EEr） are measured when nc-Si：Er is excited by 1. 519 eV or higher excitation photon energy（Eex）. Although the Eex of 1.42 eV exceeds the peak energies of Enc-Si and EEr the Enc-Si and EE, emissions are unobserved. A resonant enhancement of the EEr emission is observed in nc-Si：Er. While the PL peak intensitiy of the Enc-Si transition is quenched under this Eex. The resonant-enhanced effect in nc-Si ：Er indicates that the energy transfer process of carriers from nc-Si to nearby Er ions is enhanced by resonant excitation.