Temperature Dependence Of Photoluminescence Intensity Research Articles

Alloy compositional fluctuation in InAlGaN epitaxial films

The quaternary InAlGaN films were grown by metal-organic vapor phase epitaxy (MOVPE) at various temperatures and the optical and structural properties of the quaternary films were investigated by temperature-dependent photoluminescence (PL), high-resolution X-ray diffraction (HRXRD) and high-resolution electron microscopy (HREM). The results show that the temperature-dependent PL intensity of the InAlGaN film is similar to that of the disordered alloys, which is thought to be due to local alloy compositional fluctuations (ACF) in the epilayer. HRXRD measurement reveals there are In-rich and In-poor phases in the film and HREM observation, on the other hand, demonstrates that nanoclusters formed in the epilayer. Therefore the experimental results support the existence of ACF in the epilayers.

Phosphorescence Decay Process of Ir(ppy)3 : Temperature Dependence of Decay Time

Theoretical calculation has been undertaken on the photoluminescence (PL) lifetime of fac tris(2-phenylpyridine) iridium (Ir(ppy)3) doped in polymethyl methacrylate (PMMA) and 4,4'-N,N'-dicarbazole-biphenyl (CBP), and its temperature dependence at 0–300 K. The emitting triplet state consists of three zero-field splitting substates. Taking into account one-phonon non-radiative transitions among these substates, the rate equations for the populations of these substates are solved numerically and three PL lifetimes are derived. The long PL lifetime increases considerably with decreasing temperature from 300 to 0 K, while the two short lifetimes increase very little. A good agreement has been obtained for the temperature dependence between the calculated long lifetime and the observed one for Ir(ppy)3 in PMMA and CBP. Temperature dependence of PL intensity has been also calculated under the three-substate model. The result is consistent with the observed temperature-independence of intensity.

Energy-Back-Transfer Process in Rare-Earth Doped AlGaN

AbstractTemperature dependence of time-resolved photoluminescence (PL) properties for rare-earth ions (REIs: Eu, Tb, and Er) implanted AlxGa1-xN (x=0∼1) is investigated. Thermal quenching for RE-related PL becomes small when increasing the Al contents. The PL decay time of REIs used in the present work becomes shorter when increasing the temperature and/or PL peak energy. The temperature dependence of PL intensity and the decay time are analysed by assuming phonon assisted energy-back-transfer model, in which the energy in REIs escape to trap levels. From the results, the improvement of PL properties can be well explained by the model, in which the activation energy for energy-back-transfer process is increased as increasing the Al contents.

Temperature-dependent photoluminescence in meso-porous MCM nanotubes

Temperature-dependent photoluminescence (PL) was exploited to investigate the mechanism of luminescence of MCM (Mobil Composition of Matter)-41 and MCM-48 nanotubes. The PL intensity has a maximum around 40 K. Localization of the carriers involved in the radiative recombination was deduced from the PL decay profiles at various energies. A model based on competition between radiative recombination of localized carriers and nonradiative recombination is suggested to explain the temperature-dependence of PL intensity. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Temperature dependence of photoluminescence intensity from AlGaInP/GaInP multi-quantum well laser structures

AlGaInP/GaInP multiple quantum well laser structure was grown by low-pressure metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine. Photoluminescence (PL) measurements were performed from 10 to 230 K. The PL energy increased with temperature from 10 to 70 K and decreased above 70 K. The former was attributed to thermal activation of trapped carriers due to localization in the quantum wells, while the latter was attributed to temperature-induced band-gap shrinkage. The PL intensity as a function of temperature was fitted by employing two nonradiative recombination mechanisms with good agreement, resulting in two activation energies that correspond to losses of photogenerated carriers to nonradiative centers.

Optical properties of photo-oxidized polyfluorene thin films

Optical properties of photo-oxidized polyfluorene (PFO), which is of practical important information for PFO based polymer light emitting diodes, have been studied by photoluminescence (PL) spectroscopy. PFO thin films were oxidized by the irradiation of a He-Cd laser (1 = 325 nm) and the photo-oxidized states were characterized by optical absorption, Fourier transform infrared absorption and electron spectroscopy for chemical analysis measurements. Temperature dependence of PL intensity of PFO is well described by a thermal quenching model, from which it is found that non-radiative decay enhances by photo-oxidation and that the height of potential barrier for the singlet excited states to the oxygen-related quenching centers is ∼ 50 meV.

A comparative study of the photoluminescence properties of a-SiO x:H film and silicon nanocrystallites

Photoluminescence (PL) properties in a-SiO x and silicon crystallites with nanometer dimensions were compared to investigate recombination processes and to reveal the effect of a-SiO x on silicon crystallites. The PL spectra and temperature dependence of PL intensity of a-SiO x (where x>1) and silicon crystallites surrounded by SiO x layer shared some similarities. These results indicate that the PL peak found near 1.6 eV has its origin in the SiO x layer at the surface of the silicon core. Recombination processes are discussed by temperature dependence and lifetime of PL spectra. The PL intensity of silicon crystallites at room temperature originates from reduction of the non-radiative recombination probability rather than increase in the radiative one.

Temperature dependence of photoluminescence intensity and decay in GeSe 2 glass

The intensity and decay profile of the photoluminescence (PL) in glassy GeSe 2 are measured as a function of temperature from 2 to 200 K. The intensity decreases exponentially in the temperature region >100 K. The complicated temperature dependence of the decay profile as well as the dependence of the intensity are explained in a unified framework by adopting a model of the luminescent sites whose thermal activation energy for the non-radiative process is distributed. We show that the intensity variation is affected by the non-radiative process while the decay life time depends almost only on the radiative transition rate.

Temperature Dependence of Photoluminescence Intensities of Undoped and Doped GaN

We discuss the temperature dependence of various photoluminescence transitions observed in undoped and doped GaN in the 9 to 300 K range. Samples grown using different techniques have been assessed. The mechanism underlying the various quenching behaviors observed is investigated using simple rate equations. In undoped GaN, the temperature dependence of the band edge excitonic lines is well described by assuming that the A exciton population is the leading term in the 50 to 300 K range. The activation energy for free exciton quenching is of the order of the Rydberg, suggesting that free hole release leads to non-radiative recombination. In slightly p-doped samples, the luminescence is dominated by acceptor-related transitions, whose intensity is also governed by release of free holes. For large p-type doping (p(300 K) ≥ 1017 cm—3), the activation energy for quenching is in the 60 to 90 meV range.

Temperature Dependence of Photoluminescence Intensities of Undoped and Doped GaN

Temperature Dependence of Photoluminescence Intensities of Undoped and Doped GaN

Luminescence and Energy Transfer in Thin Films of SrGa2 S 4 : Ce

Excitation and photoluminescence (PL) spectra of both nominally undoped and thin films have been measured at various temperatures between 10 and 300 K. The undoped film shows a complex emission band which appears to involve emission from different defect states. Each defect center effects the recombination kinetics and luminescence spectra in a different temperature region. At 77 K, recombination is dominated by the highly associated defect centers producing an intense red emission band. At higher temperatures, thermalization effects reduce the net capture rates at the competitive defect centers, and recombination through the defect centers at room temperature produces a broad emission band with the peak in the blue spectral region. Evidence of the interaction and energy exchange between defect centers and activator states is inferred from the rise and decay time measurements of PL emission in thin films. As a result of thermalization, the efficiency of energy transfer to ions increases at room temperature but at the expense of introducing a long afterglow into the activator decay. Measurements of temperature dependence of PL intensity suggest that the kinetic model for energy transfer in combines aspects of long‐range resonance transfer and indirect thermalization from defect states with subsequent retrapping at the activator sites. In addition, possible mechanisms are discussed which may explain the observed concentration dependence of the fluorescence decay time. Preliminary results are reported for a thin‐film electroluminescent device with a , Li phosphor layer prepared by the low‐temperature deposition from binary vapors process. © 1999 The Electrochemical Society. All rights reserved.

Hydrogenated amorphous silicon deposited by glow discharge of SiH4 diluted with He: photoluminescence and electroluminescence in the visible region

Samples of a-Si:H having a wide gap (≥2.1 eV) were prepared using routine rf glow discharge decomposition of silane (SiH4) strongly diluted with He. Also, microwave electron–cyclotron–resonance plasma-enhanced chemical-vapour-deposition was used to prepare wide-gap a-Si:H via decomposition of He diluted SiH4. The wide-gap a-Si:H samples, containing above 30 at.% of hydrogen, exhibit visible photoluminescence at room temperature. From the temperature dependence of photoluminescence intensity and from the observed shift of the maximum with temperature we deduce that the customary model of radiative recombination of carriers localised in tail states is not directly applicable to the case of wide-gap a-Si:H. Instead, we propose that the photoluminescence arises in parallel from tail states and from isolated (extrinsic) centres. Electroluminescence results obtained on a p–i–n structure with wide-gap a-Si:H are reported.

Effects of temperature and ZnSe well-layer thickness on PL in ZnSe/ZnS strained-layer superlattices

A study of the photoluminescence (PL) spectra in ZnSe–ZnS strained layer superlattices (SLSs) with various ZnSe well-layer thicknesses was investigated by PL measurements. An intense excitonic-emission line, and no emissions due to deep levels, were observed. As the ZnSe well-layer thickness is decreased, the peak of the line largely shifted towards the higher-energy side. This behavior may be related to the quantum size effect. In the temperature dependence of PL intensity, this is the thermal quenching process, which may be related to the thermal release of excitons in the quantum well. As the thickness of the ZnSe well-layer is decreased, the activation energy increased.

Influence of Oxygen on Er-Related Emission in Gan With a Large Yellow Band

AbstractIn order to investigate the luminescence properties of Er3+in GaN and the effect of oxygen (O) on Er3+ -related emission in GaN:Er, erbium (Er) ions were implanted into single-crystal h-GaN grown on a c-axis sapphire substrate at an energy of 2MeV. Oxygen ions were subsequently coiniplanted into GaN with Er ions. The influence of oxygen on Er-related emission in GaN with a large yellow band was studied by comparing photoluminescence (PL) measurements of GaN:Er and GaN:ErO. It was found that the optimum annealing temperature to obtain maximum PL intensity was 1200°C and that the E3+a-related PL intensities from GaN:ErO samples were negligibly enhanced in comparison with the GaN:Er samples. The temperature dependence of PL intensity in GaN:ErO showed no appreciable difference from that of GaN:Er. But good correlation between Er-related and a large yellow band emission was observed in GaN. This indicates that codoped oxygen ions influence Er-related and yellow band emission in GaN

Temperature dependence of photoluminescence intensity from AlGaInP/GaInP-quantum well structures

The photoluminescence (PL) intensity of AlGaInP/GaInP-quantum well structures under a continuous excitation condition was measured as a function of the crystal temperature (10–450 K). The thermal emission of carriers from the well layers to the barrier layers was investigated by generating the carriers only in the wells. The dependence of the PL intensity on the crystal temperature was analyzed by fitting a model function to the experimental results. The rapid decrease in PL intensity at temperatures higher than 200 K was found to be probably due to the emission of carriers into the barrier layers. The effective barrier heights obtained by the fitting are in good agreement with the band-energy alignment schemes of these crystals. When AlInP barrier layers were inserted directly beside the quantum wells, the emission of carriers to the quaternary layers through the AlInP layers was reduced, resulting in stronger PL intensity at higher temperatures and a larger effective barrier height.

High photoluminescence efficiency of InGaAs/GaAs quantum dots self-formed by atomic layer epitaxy technique

We investigated the photoluminescence (PL) intensity of InGaAs/GaAs quantum dots self-formed by atomic layer epitaxy (ALE) technique as a function of temperature. We report that the reduction of PL intensity following a temperature increase was two-orders smaller in the ALE-grown dots than in the dots grown by molecular beam epitaxy via Stranski–Krastanov mode. Measuring the radiative lifetimes and evaluating the temperature dependence of PL intensity, we conclude that the nonradiative channel outside the dots caused the PL reduction.

Luminescence properties of ZnSe films grown by hot wall epitaxy

The photoluminescence (PL) properties of ZnSe films grown by hot wall epitaxy are reported. The PL spectra show clear neutral donor-bound exciton peak; donor acceptor pair (DAP) peak, conduction band to acceptor (CA) peak, and their phonon replicas until fourth order. The conduction band to acceptor peak and it's phonon replicas exist until room temperature. From the ratio of PL intensities of DAP and CA peaks and their replicas, we obtain the Huang-Rhys factor S = 0.58, in agreement with other experiments for acceptor-bound exciton transitions. From the temperature dependence of PL intensities we derive the activation energy of thermal quenching process for the DAP transitions as about 7 meV.

Direct optical transitions in indirect-gap (Al0.5Ga0.5)0.51In0.49P by atomic ordering.

(${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${)}_{\mathit{y}}$${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$P alloys naturally constitute monolayer superlattices on GaAs(001) substrates by atomic ordering when they are grown by organometallic vapor-phase epitaxy. The spontaneous long-range ordering causes the band-gap reduction and band splitting at the valence-band maximum. When the Al composition in a (${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${)}_{0.5}$${\mathrm{In}}_{0.5}$P-random alloy is larger than \ensuremath{\sim}0.4, the optical transition is indirect, and the conduction-band minimum is at ${\mathit{X}}_{6\mathit{c}}$. From electroreflectance and photoluminescence measurements, we have found for long-range ordered (${\mathrm{Al}}_{0.5}$${\mathrm{Ga}}_{0.5}$${)}_{0.51}$${\mathrm{In}}_{0.49}$P that the ${\mathrm{\ensuremath{\Gamma}}}_{6\mathit{c}}$ valley crosses the ${\mathit{X}}_{6\mathit{c}}$ by the band-gap reduction. The emission from the strongly ordered alloy is optically direct. The temperature dependence of photoluminescence intensity shows that statistical potential fluctuations and localized states in the low-energy part of the exciton resonance play an important role in the direct luminescence of the long-range ordered (${\mathrm{Al}}_{0.5}$${\mathrm{Ga}}_{0.5}$${)}_{0.51}$${\mathrm{In}}_{0.49}$P. \textcopyright{} 1996 The American Physical Society.

Passivation of surface and bulk defects in p -GaSb by hydrogenated amorphous silicon treatment

Passivation of point and extended defects in GaSb has been observed as a result of hydrogenated amorphous silicon (a-Si:H) treatment by the glow discharge technique. Cathodoluminescence (CL) images recorded at various depths in the samples clearly show passivation of defects on the surface as well as in the bulk region. The passivation of various recombination centers in the bulk is attributed to the formation of hydrogen-impurity complexes by diffusion of hydrogen ions from the plasma. a-Si:H acts as a protective cap layer and prevents surface degradation which is usually encountered by bare exposure to hydrogen plasma. An enhancement in luminescence intensity up to 20 times is seen due to the passivation of nonradiative recombination centers. The passivation efficiency is found to improve with an increase in a-Si:H deposition temperature. The relative passivation efficiency of donors and acceptors by hydrogen in undoped and Te-compensated p-GaSb has been evaluated by CL and by the temperature dependence of photoluminescence intensities. Most notably, effective passivation of minority dopants in tellurium compensated p-GaSb is evidenced for the first time.

Photoluminescence from a Silicon Quantum Well Formed on Separation by Implanted Oxygen Substrate

We have observed strong photoluminescence (PL) from a well-defined two-dimensional (2D) Si structure formed on a SIMOX (separation by implanted oxygen) wafer, where the thin ( <5 nm) single crystalline silicon film is sandwiched between SiO2 layers. The PL intensity has a sharp maximum at a Si thickness of about 2 nm, whereas the peak photon energy of the PL spectra (1.65 eV) is almost independent of the Si thickness. These results can be interpreted with a three-region model in which electron-hole pairs are excited in the Si well and luminescence occurs at the upper and lower Si/SiO2 interfaces. Furthermore, temperature dependence of PL intensity in the present 2D system is found to be different from previously reported dependence in 0D or 1D Si structures.