Enhancing redshift phenomenon in time-resolved photoluminescence spectra of AlGaN epilayer

AlGaN epitaxial layer has been studied by means of temperature-dependent time-integrated photoluminescence（PL）and time-resolved photoluminescence（TRPL）. An enhancing redshift phenomenon in TRPL spectra with increasing temperature was observed, and the localized excitons behaved like quasi two-dimensional excitons between 6 K and 90 K. We demonstrated that these behaviors are caused by a change in the carrier dynamics with increasing temperature due to the competition of carriers＇ localization and delocalization in the AlGaN alloy.

Time-Resolved Photoluminescence Study of Silicon Nanoporous Pillar Array

A silicon nanoporous pillar array （Si-NPA） is thought to be a promising functional substrate for constructing a variety of Si-based optoelectronic nanodevices, due to its unique hierarchical structure and enhanced physical properties. This makes the in-depth understanding of the photoluminescence （PL） of Si-NPA crucial for both scientific research and practical applications. In this work, the PL properties of Si-NPA are studied by measuring both the steady-state and time-resolved PL spectrum. Based on the experimental data, the three PL bands of Si-NPA, i.e., the ultraviolet band, the purple-blue plateau and the red band are assigned to the oxygen-excess defects in Si oxide or silanol groups at the surface of Si nanocrystallites （nc-Si）, oxygen deficiency defects in Si oxide, and band-to-band transition of nc-Si under the frame of quantum confinement combining with the surface states like Si=O and Si-O^i bonds at the surface of nc-Si, respectively. These results may provide some novel insight into the PL process of Si-NPA and may be helpful for clarifying the PL mechanism.

Time-Resolved Photoluminescence Spectra of Porous Si

he photoluminescence spectra of porous Si have been studied. Its timere-solved luminescence spectra show a red shift of luminescencc peak with increasingdelay time after exciting and a nonexponential decay. Several spectral bands withdifferent Gaussian center appear by means of the decomposition of a spetrum. Theresuits of our experiments show quantum confined characters in porous Si, and wespeculate that the short wavelength band at 465 nm is the direct band froni P_(15) toP_(25)

Linear and nonlinear characteristics of time-resolved photoluminescence modulation by terahertz pulse

The linear and nonlinear characteristics of time-resolved photoluminescence （PL） of n-type bulk semiconductor GaAs modulated with terahertz （THz） pulse are studied by using an ensemble Monte Carlo （EMC） method. In this paper the center energy valley （Г valley） electron concentration changes with the pulse delay time, sampling time and the outfield are mainly discussed. The results show that the sampling time and the THz field should exceed certain thresholds to effectively excite photoluminescence quenching （PLQ）. Adopting a direct current （DC） field makes the sampling time threshold shortened and the linear range of THz field-modulation PL expanded. Moreover, controlling the sampling time and the outfield intensity can improve the linear quality： with forward time, the larger outfield is used; with backward time, the smaller outfield is used. This study can provide a theoretical basis of THz field linear modulation in a larger range for new light emitting devices.

Diffusion effect on the decay of time-resolved photoluminescence under low illumination in lead halide perovskites

Time-resolved photoluminescence(TRPL)has been extensively used to measure the carrier lifetime in lead halide perovskites.The TRPL curves of perovskite materials are usually fitted with a multi-exponential function,instead of a single exponential one.This was considered to be a result of the surface and the bulk recombination or the additional radiative recombination caused by the high excited carrier density.Here,a new model considering the diffusion and the trap-assisted recombination of carriers is proposed to explain the TRPL curves.The expressions of the TRPL curves and the transient absorption(TA)dynamic curves are theoretically derived,demonstrating that the TRPL curve is an infinite exponential series,regardless of the presence of surface recombination or not.Our newly developed highly sensitive nanosecond TA and TRPL were employed to measure the carrier dynamics of the same sample under low illumination in the linear response region of TA,thereby experimentally verifying our model.These results suggest that the decay of the TRPL is not only a consequence of the carrier recombination but also the carrier diffusion.TRPL cannot provide a direct measurement of the carrier lifetime,whereas TA spectroscopy can.Furthermore,the surface and the bulk recombination can be resolved and the average diffusion coefficient(D)can also be correctly obtained by combining TRPL and TA measurements.We also propose an approximate method for calculating the carrier lifetime and diffusion coefficient of high-quality perovskite films.Our model provides not only a new interpretation of the dynamics of the PL decay but also a deep insight into the carrier dynamics in the nanosecond time scale under working condition of perovskites solar cells.

Ultrafast carrier dynamics in GeSn thin film based on time-resolved terahertz spectroscopy

We measure the time-resolved terahertz spectroscopy of GeSn thin film and studied the ultrafast dynamics of its photo-generated carriers.The experimental results show that there are photo-generated carriers in GeSn under femtosecond laser excitation at 2500 nm,and its pump-induced photoconductivity can be explained by the Drude–Smith model.The carrier recombination process is mainly dominated by defect-assisted Auger processes and defect capture.The firstand second-order recombination rates are obtained by the rate equation fitting,which are(2.6±1.1)×10^(-2)ps^(-1)and(6.6±1.8)×10^(-19)cm^(3)·ps^(-1),respectively.Meanwhile,we also obtain the diffusion length of photo-generated carriers in GeSn,which is about 0.4μm,and it changes with the pump delay time.These results are important for the GeSn-based infrared optoelectronic devices,and demonstrate that Ge Sn materials can be applied to high-speed optoelectronic detectors and other applications.

Ostensibly perpetual optical data storage in glass with ultra-high stability and tailored photoluminescence

Long-term optical data storage(ODS)technology is essential to break the bottleneck of high energy consumption for information storage in the current era of big data.Here,ODS with an ultralong lifetime of 2×10^(7)years is attained with single ultrafast laser pulse induced reduction of Eu^(3+)ions and tailoring of optical properties inside the Eu-doped aluminosilicate glasses.We demonstrate that the induced local modifications in the glass can stand against the temperature of up to 970 K and strong ultraviolet light irradiation with the power density of 100 kW/cm^(2).Furthermore,the active ions of Eu^(2+)exhibit strong and broadband emission with the full width at half maximum reaching 190 nm,and the photoluminescence(PL)is flexibly tunable in the whole visible region by regulating the alkaline earth metal ions in the glasses.The developed technology and materials will be of great significance in photonic applications such as long-term ODS.

Photoluminescence Enhancement of Aluminum Ion Intercalated MoS_(2)Quantum Dots

Low photolumines-cence(PL)quantum yield of molybdenum disulfide(MoS_(2))quan-tum dots(QDs)has lim-ited practical applica-tion as potential fluores-cent materials.Here,we report the intercalation of aluminum ion(Al^(3+))to enhance the PL of MoS_(2)QDs and the un-derlying mechanism.With detailed characterization and exciton dynamics study,we suggest that additional surface states including new emission centers have been effectively introduced to MoS_(2)QDs by the Al^(3+)intercalation.The synergy of new radiative pathway for exciton re-combination and the passivation of non-radiative surface traps is responsible for the en-hanced fluorescence of MoS_(2)QDs.Our findings demonstrate an efficient strategy to improve the optical properties of MoS_(2)QDs and are important for understanding the regulation effect of surface states on the emission of two dimensional sulfide QDs.

Time-resolved K-shell x-ray spectra of nanosecond laser-produced titanium tracer in gold plasmas

A study of a nanosecond laser irradiation on the titanium-layer-buried gold planar target is presented. The timeresolved x-ray emission spectra of titanium tracer are measured by a streaked crystal spectrometer. By comparing the simulated spectra obtained by using the FLYCHK code with the measured titanium spectra, the temporal plasma states, i.e.,the electron temperatures and densities, are deduced. To evaluate the feasibility of using the method for the characterization of Au plasma states, the deduced plasma states from the measured titanium spectra are compared with the Multi-1D hydrodynamic simulations of laser-produced Au plasmas. By comparing the measured and simulated results, an overall agreement for the electron temperatures is found, whereas there are deviations in the electron densities. The experiment–theory discrepancy may suggest that the plasma state could not be well reproduced by the Multi-1D hydrodynamic simulation, in which the radial gradient is not taken into account. Further investigations on the spectral characterization and hydrodynamic simulations of the plasma states are needed. All the measured and FLYCHK simulated spectra are given in this paper as datasets. The datasets are openly available at http://www.doi.org/10.57760/sciencedb.j00113.00032.

Temperature-dependent photoluminescence of lead-free cesium tin halide perovskite microplates

Tin halide perovskites recently have attracted extensive research attention due to their similar electronic and band structures but non-toxicity compared with their lead analogues. In this work, we prepare high-quality CsSnX_(3)(X=Br,I) microplates with lateral sizes of around 1–4 μm by chemical vapor deposition and investigate their low-temperature photoluminescence(PL) properties. A remarkable splitting of PL peaks of the CsSnBr_(3)microplate is observed at low temperatures. Besides the possible structural phase transition at below 70 K, the multi-peak fittings using Gauss functions and the power-dependent saturation phenomenon suggest that the PL could also be influenced by the conversion from the emission of bound excitons into free excitons. With the increase of temperature, the peak position shows a blueshift tendency for CsSnI_(3), which is governed by thermal expansion. However, the peak position of the CsSnBr3microplate exhibits a transition from redshift to blueshift at ~160 K. The full width at half maximum of CsSnX_(3)broadens with increasing temperature, and the fitting results imply that longitudinal optical phonons dominate the electron–phonon coupling and the coupling strength is much more robust in CsSnBr3than in CsSnI_(3). The PL intensity of CsSnX_(3)microplates is suppressed due to the enhanced non-radiative relaxation and exciton dissociation competing with radiative recombination. According to the Arrhenius law, the exciton binding energy of CsSnBr_(3)is ~38.4 meV, slightly smaller than that of CsSnI_(3).

Anomalous photoluminescence enhancement and resonance charge transfer in type-II 2D lateral heterostructures

Type-Ⅱband alignment can realize the efficient charge transfer and separation at the semiconductor heterointerface,which results in photoluminescence(PL)quenching.Recently,several researches demonstrated great enhancement of localized PL at the interface of type-Ⅱtwo-dimensional(2D)heterostructure.However,the dominant physical mechanism of this enhanced PL emission has not been well understood.In this work,we symmetrically study the exciton dynamics of type-Ⅱlateral heterostructures of monolayer MoS_(2) and WS_(2) at room temperatures.The strong PL enhancement along the one-dimensional(1D)heterointerface is associated with the trion emission of the WS_(2) shell,while a dramatic PL quenching of neutral exciton is observed on the MoS_(2) core.The enhanced quantum yield of WS2trion emission can be explained by charge-transfer-enhanced photoexcited carrier dynamics,which is facilitated by resonance hole transfer from MoS_(2) side to WS_(2) side.This work sheds light on the 1D exciton photophysics in lateral heterostructures,which has the potential to lead to new concepts and applications of optoelectronic device.

Thermally enhanced photoluminescence and temperature sensing properties of Sc2W3O12:Eu3+ phosphors

Recently, lanthanide-ion-doped luminescent materials have been extensively used as optical thermometry probes due to their fast responses, non-contact, and high sensitivity properties. Based on different responses of two emissions to temperature, the fluorescence intensity ratio(FIR) technique can be used to estimate the sensitivities for assessing the optical thermometry performances. In this study, we introduce different doping concentrations of Eu^(3+) ions into negative thermal expansion material Sc2W3O12to increase the thermal-enhanced luminescence from 373 K to 548 K, and investigate the temperature sensing properties in detail. All samples can exhibit their good luminescence behaviors thermally enhanced.The emission intensity of Sc2W3O12:6-mol% Eu3+phosphor reaches 147.8% of initial intensity at 473 K. As the Eu3+doping concentration increases, the resistance of the sample to thermal quenching decreases. The FIR technique based on each of the transitions 5D→7F_(1)(592 nm) and 5D→7F_(2)(613 nm) of Eu3+ions demonstrates a maximum relative temperature sensitivity of 3.063% K-1at 298 K for Sc_(2)W_(3)O_(12):6-mol% Eu3+phosphor. The sensitivity of sample decreases with the increase of Eu3+concentration. Benefiting from the thermal-enhanced luminescence performance and good temperature sensing properties, the Sc_(2)W_(3)O_(12):Eu^(3+)phosphors can be used as optical thermometers.

Structural and band tail state photoluminescence properties of amorphous SiC films with different amounts of carbon

Amorphous silicon carbide films are deposited by the plasma enhanced chemical vapour deposition technique,and optical emissions from the near-infrared to the visible are obtained.The optical band gap of the films increases from 1.91 eV to 2.92 eV by increasing the carbon content,and the photoluminescence（PL） peak shifts from 1.51 eV to 2.16 eV.The band tail state PL mechanism is confirmed by analysing the optical band gap,PL intensity,the Stocks shift of the PL,and the Urbach energy of the film.The PL decay times of the samples are in the nanosecond scale,and the dependence of the PL lifetime on the emission energy also supports that the optical emission is related to the radiative recombination in the band tail state.

Thickness Dependent Behavior of Photoluminescence of Tris(8-hydroxyquinoline)Aluminum Film

通过原位测量对八-羟基喹啉铝薄膜(Alq_3)光致发光的厚度依赖性质进行了研究.在 Alq_3向玻璃衬底沉积的初始阶段,Alq_3光致发光谱峰发生了显著红移,此后谱峰随着 Alq_3厚度的增加红移变缓并趋于饱和.Alq_3薄膜厚度从2nm 逐渐变化到500nm 时,Alq_3谱峰位总红移约为12nm.这种 Alq_3薄膜沉积的初始阶段 Alq_3谱峰的显著红移可归因于二维激子向三维激子态的转变.同时,由于激子同衬底的相互作用所引起的非辐射衰变,在 Alq_3沉积的初始阶段 Alq_3光致发光谱峰的强度呈现不同的变化,随后该谱峰的强度随 Alq_3薄膜厚度的增加而快速增加,并在薄膜厚度较大时,趋向于饱和.

Hydrothermal synthesis and photoluminescence behavior of CeO_2 nanowires with the aid of surfactant PVP

Well-crystalline CeO_2 nanowires were prepared via a surfactant-assisted hydrothermal process.Reaction temperature and reaction time were changed for the determination of optimal synthesis parameters.The as-obtained products were characterized by X-ray diffraction （XRD）,high-resolution transmission electron microscopy（HRTEM）,and field emission scanning electron microscopy（FESEM）.The results show that single crystal CeO_2 nanowires with high yield and good uniformity can be obtained hydrothermally at 180℃for 12 h with the aid of 2.0 g surfactant（polyvinyl pyrrolidone,PVP）.The role of PVP was then discussed and a possible growth mechanism was proposed. Moreover,room temperature photoluminescence（PL） spectra were obtained for these CeO2 nanowires,which are believed to be related to the abundant defects in these nanostructures.

A Series of Mononuclear Complexes Constructed from Transition Metals and Amino Acid Derived Ligands: Syntheses, Structures and Photoluminescence

Eight neutral mononuclear complexes constructed from transition metals （M = Co（Ⅱ）, Ni（Ⅱ）, Cu（Ⅱ）, Zn（Ⅱ）, Cd（Ⅱ）） and ligands N-（2-pyridylmethyl）-L-phenylalanine （L-Hpmpa） and N-（2-pyridylmethyl）-L-tyrosine （L-Hpmtyr） have been synthesized by both hydrothermal and conventional room temperature reactions. Four of them have been structurally characterized by single-crystal X-ray diffractions. They are： [Co（L-pmpa）2·2H2O] 1, [Ni（L-pmpa）2·2H2O] 2, [Cu（L-pmpa）2·2H2O] 3 and [Cu（L-pmtyr）2·2H2O] 4. Single-crystal X-ray analysis, IR and elemental analysis revealed that complexes 1, 2 and 3 are isostructural. Powder X-ray diffraction, IR and elemental analysis revealed that complexes 4, 5 （Zn[L-pmtyr]2·2H2O）, 6 （Cd[L-pmtyr]2·2H2O）, 7 （Co[L-pmtyr]2·2H2O） and 8 （Ni[L-pmtyr]2·2H2O） are isostructural. The photoluminescence properties of L-Hpmtyr ligand, compounds 5 and 6 were also investigated.

Preparation, Structure, Photoluminescence and Energy Transfer Mechanism of a Novel Holmium Complex

A novel holmium complex [Ho(HIA)_2(H_2O)_4(NO_3)](NO_3)_2(1, HIA = isonicotinic acid) has been synthesized through hydrothermal reactions and characterized by single-crystal X-ray diffraction. Complex 1 crystallizes in the C2/c space group of monoclinic system: a = 14.4797(7), b = 12.4768(2), c = 13.3471(5) ?, β = 118.690(4)°, V = 2115.26(13) ?~3, C_(12)H_(16)HoN_5O_(17), Mr = 667.23, Z = 4, Dc = 2.095 g/cm^3, μ(Mo Kα) = 3.838 mm^(–1) and F(000) = 1304. The crystal structure of 1 is characterized by an isolated structure. Solid-state photoluminescence experiment uncovers that it shows yellow light emission. The emission bands are originated from the characteristic emission of the 4 f electrons intrashell transition of the ~5S_2 → ~5I_8 and ~5F_5 → ~5I_8 of the Ho^(3+) ions. Energy transfer mechanism is explained by the energy level diagram of the Ho3+ ion and the isonicotinic acid ligand. It has remarkable CIE chromaticity coordinates of(0.4929, 0.4632), so it may be a promising color converter for lighting and displays.

Structure and visible photoluminescence of Sm^3＋, Dy^3＋ and Tm^3＋ doped c-axis oriented AlN films

Visible photoluminescence （PL） has been observed from rare earth （Tm, Sm and Dy）-doped AlN films grown by radio-frequency magnetron reactive sputtering. X-ray diffraction indicates that the films are c-axis-oriented hexagonal wurtzite type structure with an average crystal size of about 80-110 nm. Room-temperature PL spectra indicate that the blue emission is due to the transition of ^1D2 to ^3F4 and ^1G4 to ^3H6 intra 4f electron of Tm^3＋, the yellow emissions of AlN：Sm are due to ^4G5/2 to the ^6HJ （J=5/2, 7/2, 9/2, 11/2） and the reddish emissions of AlN：Dy correspond to the ^4F9/2 to ^6HJ （J=5/2, 13/2, 11/2 and 9/2） and ^6Fll/2 transitions.

Photoluminescence of multiwalled carbon nanotubes excited at different wavelengths

In this paper the multiwalled carbon nanotubes （MWNTs） were synthesized by a chemical vapour deposition and the SEM graph shows that the sample has good construction. The micro-Raman spectrum shows the characteristic line of the MWNTs and an additional line produced by the defects on the outer surface of MWNTs. The photoluminescence （PL） spectra observed experimentally are variable under different excitation wavelengths and the strong excitation wavelength dependence of luminescence indicates a distribution of emitters which include electron π in excited states and the Van Hove singularities. The absorption spectra confirm the transition channels which are consistent with the PL emission.

Upconversion Photoluminescence and Energy Transfer Mechanism of a Novel Terbium-mercury Compound

A novel terbium-mercury complex [Tb(IA)3(H3 O)2]2 n(2 n HgCl4)(n Hg2 Cl5)·n H3 O· 3 n H2 O(1, HIA = isonicotinic acid) has been synthesized through hydrothermal reactions and characterized by single-crystal X-ray diffraction. Complex 1 crystallizes in the C2/c space group of monoclinic system with a = 24.2347(5), b = 20.8342(6), c = 15.3206(3) ?, β = 128.257(2)°, V = 6074.3(2) ?3, C36H41Cl13Hg4N6O20Tb2, Mr = 2458.80, Z = 4, Dc = 2.689 g/cm3, μ(Mo Kα) = 13.014 mm–1 and F(000) = 4520. The crystal structure of 1 is characterized by a one-dimensional(1-D) chain-like structure. Solid-state UV/Vis diffuse reflectance spectrum reveals the existence of a wide optical band gap of 3.36 eV. Solid-state photoluminescence experiment uncovers that it shows reddish brown upconversion emission. The emission bands are originated from the characteristic emission of the 4 f electrons intrashell transition of the 5D4 → 7 FJ(J = 6, 5, 4) of the Tb3+ ions. Energy transfer mechanism is explained by the energy level diagram of the Tb3+ ion and the isonicotinic acid ligand. It shows a remarkable CIE chromaticity coordinates(0.4158, 0.4005).