Short Decay Time Research Articles

Structural and spectral studies of highly pure red-emitting Ca3B2O6:Eu3+ phosphors for white light emitting diodes

• Ca 3 B 2 O 6 :Eu 3+ phosphors were investigated as an alternative for red light. • Highly pure red emission was realized upon near UV excitation. • The phosphor has high color purity ~ 90%. Near UV excited highly pure red light emitting Ca 3 B 2 O 6 :Eu 3+ phosphor was synthesized via a solution combustion method. The prepared samples were examined using Powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and Photoluminescence (PL) spectroscopy for their structural, spectral, surface, and luminescent studies. The XRD and FTIR results showed the formation of a single phase Ca 3 B 2 O 6 compound with BO 3 and BO 4 structural units. PL emission spectra under near UV excitation show characteristic emission for the Eu 3+ ion ( 5 D 0 → 7 F j , j = 0, 1, 2, 3 and 4) with the main red emission peak at 614 nm corresponding to the 5 D 0 → 7 F 2 transition state of the Eu 3+ ion. The XPS results depicted that all the elements were presented on the surface of the material and the Eu ion was presented in the (+3) state. The density of states and bandgap of the material was approximated by employing the density functional theory. Moreover, the decay time, International Commission on Illumination coordinates, and color purity were also calculated. Phosphor with short decay time, CIE coordinates corresponds to strong red emission and high color purity reveal that the phosphor can be a potential material as a red component for white light emitting diodes (wLED).

Syntheses, Crystal Structures and Photophysical Properties of Dinuclear Copper(I) Complexes Bearing Diphenylphosphino‐Substituted Benzimidazole Ligands

AbstractThree dinuclear copper(I) complexes (1, 2 and 3) of the form [(P N)Cu]2(μ2‐I)2 have been designed and synthesized with 4‐diphenylphosphino‐benzimidazole (P N) derivatives. X‐ray structural analysis shows that the complexes possess one rhombohedral Cu2I2 dimer that is coordinated with two P N ligands and exhibits a trans‐configuration. At 290 K, the copper complexes exhibit similar broad and featureless emission bands with peak maxima (λmax) at 585 nm, 565 nm and 586 nm, respectively. The temperature‐dependent photophysical behaviors accompanied with the theory calculations demonstrate that 1 represents a thermally activated delayed fluorescence behavior at ambient temperature, whereas luminescence of 2 and 3 is phosphorescence. Moreover, the complexes (1–3) achieve high photoluminescence quantum yields of 36.9 %, 43.0 % and 34.0 % with relatively short emission decay times of 5.85 μs, 7.99 μs and 5.99 μs, respectively. The solution‐processed organic light‐emitting diode based on 1 achieves a peak brightness of 3325 cd m−2 and an EQE of 2.99 %.

Hydrogen isotope permeation through yttria coatings on Eurofer in the diffusion limited regime

In fusion power plants a tritium permeation barrier is required in order to prevent the loss of the fuel. Moreover, the tritium permeation barrier is necessary to avoid that the radioactive tritium accumulates in the first wall, the cooling system, and other parts of the power plant. Oxide thin films, e.g. Al2O3, Er2O3 and Y2O3, are promising candidates as tritium permeation barrier layers. With regard to the application, this is especially true for yttrium due to its favorably short decay time after neutron activation compared to the other candidates. The Y2O3 layers with thicknesses from 100 nm to 500 nm are deposited on both sides of Eurofer substrates by RF magnetron sputter deposition. Some of the samples are additionally deposited with palladium thin films to analyse the limited regime. During the annealing in the experiments the palladium layers do not show any crack formation or delamination, verified by scanning electron microscopy. After annealing the cubic crystal structure of the Y2O3 layers is verified by X-ray diffraction. The cubic phase contains a small amount of a monoclinic phase, which is eliminated after the permeation measurements. The permeation reduction factors of the samples are determined in gas-driven deuterium permeation experiments. A permeation reduction of 5000 of the yttria thin film is verified. The diffusion limited regime is identified by the pressure dependence of the permeation measurement and by permeation experiments with the palladium top layers on the Y2O3 thin films. Furthermore, the activation energy of the permeation through the yttria thin films is determined. Pre-annealing times for more than 70 h of the Y2O3 thin films and permeation measurements with temperature cycles for 20 days are performed to show the stability of the permeation flux and hence the microstructure of the barrier layers. Measurement times at each constant temperature level of more than 25 h are required for the stabilization of each permeation flux to a constant value. The permeation measurement setup is enhanced to enable a continuously running equipment for these measurement times.

Unveiling Mn4+ substitution in oxyfluoride phosphor Rb2MoO2F4:Mn4+ applied to wide-gamut fast-response backlight displays

Mn4+-doped fluoride red-emitting phosphors are widely used in white light-emitting diodes (WLEDs) for wide-color-gamut backlight display. However, the long fluorescence decay time (τ > 5 ms) are easy to cause image-retention while images rapidly switch compare to Eu2+-doped red phosphors (0.2–2 μs). Herein, we report a novel Rb2MoO2F4:Mn4+ (RMOF) phosphor with short fluorescence lifetime (τ < 4 ms) and characteristic zero phonon line emission, realized via equivalent doping of [MnF6]2− into [MoO2F4]2− group lattice. Theoretical calculations reveal that the formation energy of [MnF6]2− occupying [MoO2F4]2− only needs a low energy to balance the charge mismatch between Mn4+ and Mo6+. A wide color gamut (~101.6% NTSC) WLED without obvious image-retention was fabricated by using Rb2MoO2F4:Mn4+ as red component, showing a fasterswitchingspeed than the commercial K2SiF6:Mn4+ (τ > 8 ms) based LEDs. This [MnF6]2− group equivalent doping strategy would pay a way to explore Mn4+ occupation in oxy-fluoride phosphors and open a new perspective on designing short fluorescence decay time phosphors for wide color gamut fast-response displays.

Preparation and properties of GAGG:Ce/glass composite scintillation material* *Project support by the National Natural Science Foundation of China (Grant Nos. 11975220, 51972291, 11575170, and 11605194).

The translucent GGAG:Ce/glass composites are prepared successfully by ball-milling, tableting, and pressureless sintering. The thickness of composites is about 400 μm. The x-ray diffraction (XRD), differential scanning calorimetry (DSC), density of composite materials are measured and discussed systematically. The scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) elemental mapping are employed to analyze the particle size, the shape of powders, and the distribution of GGAG:Ce particles in the glass matrix, respectively. The decay time, ultraviolet, (UV), x-ray excitation luminescence spectra, and temperature spectra are studied. The results show that the composite materials have high light output, good thermostability, and short decay time. The method adopted in this work is an effective method to reduce the preparation time and cost of the sample. The ultralow afterglow indicates that the composite materials have an opportunity to be used for x-ray detection and imaging.

Extending the potential of plasma-induced luminescence spectroscopy

In the context of laser-induced breakdown spectroscopy (LIBS), plasma-induced luminescence (PIL) may be observed by tuning the temporal acquisition parameters (delay and gate). This approach provides useful information about minor elements in a sample. The broad range of excitation resulting from the laser-induced plasma enables the simultaneous observation of multiple luminescence emission bands. However, PIL results in damage to the sample due to laser ablation. Moreover, time resolution only enables the separation of emission signatures with different decay times; as a consequence, only luminescence signatures with long decay times may be observed separately from plasma emissions. In this study, we propose a new experimental approach to extend the potential of PIL spectroscopy. Our main idea is to generate a laser-induced plasma on a separate ablation target adjacent to the luminescent sample, which is hence protected from laser ablation. Moreover, the ablation target can be selected to ensure a stable plasma for PIL excitation. We also show that this setup enables the further study of the excitation mechanisms of PIL itself by varying the nature of the excitation source of PIL. Finally, we propose a new experimental setup that enables the study of the luminescence features of short decay times. We successfully tested this new approach on both artificial and natural crystals, showing luminescence emission bands of varying decay times.

Halide-Enhanced Spin-Orbit Coupling and the Phosphorescence Rate in Ir(III) Complexes.

The spin-forbidden nature of phosphorescence in Ir(III) complexes is relaxed by the metal-induced effect of spin-orbit coupling (SOC). A further increase of the phosphorescence rate could potentially be achieved by introducing additional centers capable of further enhancing the SOC effect, such as metal-coordinated halides. Herein, we present a dinuclear Ir(III) complex Ir2I2 that contains two Ir(III)-iodide moieties. The complex shows intense phosphorescence with a quantum yield of ΦPL(300 K) = 90% and a submicrosecond decay time of only τ(300 K) = 0.34 μs, as measured under ambient temperature for the degassed toluene solution. These values correspond to a top value T1 → S0 phosphorescence rate of kr = 2.65 × 106 s-1. Investigations at cryogenic temperatures allowed us to determine the zero-field splitting (ZFS) of the emitting state T1 ZFS(III-I) = 170 cm-1 and unusually short individual decay times of T1 substates: τ(I) = 6.4 μs, τ(II) = 7.6 μs, and τ(III) = 0.05 μs. This indicates a strong SOC of state T1 with singlet states. Theoretical investigations suggest that the SOC of state T1 with singlets is also contributed by halides. Strongly contributing to the higher occupied molecular orbitals of the complex (e.g., HOMO, HOMO - 1, and so forth), iodides work as important SOC centers that operate in tandem with metals. The examples of Ir2I2 and of earlier reported analogous complex Ir2Cl2 reveal that the metal-coordinated halides can enhance the SOC of state T1 with singlets and, consequently, the phosphorescence rate. A comparative study of Ir2I2 and Ir2Cl2 shows that the share of halides in total contribution (halides plus metals) to the SOC of state T1 with singlets increases strongly upon exchange of chlorides for iodides. The exchange also led to the decrease in values of ZFS of the T1 state from ZFS(III-I) = 205 cm-1 for Ir2Cl2 to T1 ZFS(III-I) = 170 cm-1 for Ir2I2. This results in a more efficient thermal population of the fastest emitting T1 substate III, thus further enhancing the room-temperature phosphorescence rate.

Synthesis, structure and photophysical properties of two tetranuclear copper(I) iodide complexes based on acetylpyridine and diphosphine mixed ligands.

Two copper(I) iodide tetramers, namely, [μ2-1,3-bis(diphenylphosphanyl)propane-κ2P:P']di-μ3-iodido-di-μ2-iodido-[1-(pyridin-3-yl)ethan-1-one-κN]tetracopper(I) dichloromethane disolvate, [Cu4I4(C6H7NO)2(C27H26P2)2]·2CH2Cl2 (CuL3), and [μ2-1,3-bis(diphenylphosphanyl)propane-κ2P:P']di-μ3-iodido-di-μ2-iodido-[1-(pyridin-4-yl)ethan-1-one-κN]tetracopper(I), [Cu4I4(C6H7NO)2(C27H26P2)2] (CuL4), have been synthesized from reactions of CuI, 1,3-bis(diphenylphosphanyl)propane (dppp) and 3- or 4-acetylpyridine (3/4-acepy). The complexes were characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction (XRD), powder XRD and photoluminescence spectroscopy. Both complexes possess a stair-step [Cu4I4] cluster structure with a crystallographic inversion centre located in the middle of a Cu2I2 ring (Z' = 1/2). The dppp ligands each adopt a bidentate coordination mode that bridges two CuI centres on one side of the [Cu4I4] cluster and the acepy ligands act as terminal ligands. The solid-state samples of similar complexes show highly efficiency thermally activated delayed fluorescence (TADF) at room temperature. At ambient temperature, both CuL3 and CuL4 exhibit photoluminescence, with a maximum emission in the region 560-580 nm and with short emissive decay times, but only phosphorescence was observed at 77 K. The narrow gaps between the higher lying singlet state and the triplet state, ΔE(S1 - T1), also confirm the presence of TADF. Structure analysis and consideration of photoluminescence indicates that the position of the acetyl group on the heterocyclic ligand has an obvious influence on the structural arrangement, on intermolecular interactions and on the observed photophysical properties.

Structural designing of Zn2SiO4:Mn nanocrystals by co-doping of alkali metal ions in mesoporous silica channels for enhanced emission efficiency with short decay time.

High purity Zn2SiO4:Mn crystals were synthesized by impregnating a precursor solution into mesoporous silica followed by sintering process. The effects of doping alkali metal ions (Li+, Na+, K+) on the structural, morphological and photoluminescence properties were investigated. Formation of single phase α-Zn2SiO4:Mn crystals was confirmed from X-ray diffraction. The crystal size was significantly decreased from 54 nm to 35 nm with increasing molar concentration of alkali metal ion dopants in Zn2SiO4:Mn. Zn2SiO4:Mn crystals co-doped with alkali metal ions showed stronger emission and faster decay times compared to the un-doped Zn2SiO4:Mn phosphor. The highest emission quantum yields (EQEs) of 68.3% at λexc 254 and 3.8% at λexc 425 nm were obtained for the K+ ion doped samples with Mn2+ : K+ ratio of ∼1 : 1. With alkali metal ions (Li+, Na+, K+) co-doping, the decay time of Zn2SiO4:Mn crystals was shortened to ∼4 ms, whereas the emission intensity was elevated, with respect to un-doped Zn2SiO4:Mn crystals. Zn2SiO4:Mn crystal growth in silica pores together with selective doping with alkali metal ions paves a way forward to shorten the phosphor response time, without compromising emission efficiency.

Спектральное исследование фотодинамических процессов в системе C-=SUB=-60-=/SUB=--(н-метилпирролидон)-кислород

The processes of photoexcitation and energy transfer in an air-saturated solution of fullerene C60 in n-methylpyrrolidone are studied. With femtosecond laser pumping at a wavelength л(p) = 520 nm, transient absorption spectra were obtained in the range 470-750 nm. Broadband absorption is observed at л &gt; 650 nm as a result of aggregation of fullerene molecules, characterized by a short decay time of the picosecond scale. The analysis of the time dependencies indicates the presence of several processes. Within the proposed interpretation, we state a remarkable reduction in the time of singlet-triplet intersystem crossing with an increase of nanocluster size while the rapid quenching of the singlet state varies only slightly. The quantum yield of the triplet state can therefore increase, reaching 0.14. The phosphorescence spectra of singlet oxygen with a maximum at л = 1276 nm were measured with LED excitation at various wavelengths in the range 370-625 nm. The lifetime and quenching rate constant of singlet oxygen in n-methylpyrrolidone are determined. The combined quantum yield of triplet fullerene and singlet oxygen in n-methylpyrrolidone is estimated as 0.74. The efficiency spectra of the singlet oxygen photosensibilization in the C60-(n-methylpyrrolidone)-oxygen system are obtained, indicating the increasing role of large nanoclusters in this process during aging of the solution.

High count rate pulse shape discrimination algorithms for neutron scattering facilities

The performance of EJ-270, a 6Li loaded pulse shape discriminating plastic scintillator was tested for use in applications with high thermal and epithermal neutron fluxes such as neutron scattering facilities. The short decay time of EJ-270 make it of interest for high count rate applications. To realize this, 4 PSD algorithms were tested. The algorithms were selected based on the potential for high rate applications and simplicity. These algorithms were the charge integration method with and without the addition of a digital low pass filter, a measurement of the time to 10% of peak amplitude and a method we call the “tail sum” which utilizes a digital low pass filter and sums a small number of samples in the tail of each pulse. These algorithms were benchmarked using the figure of merit, the γ-sensitivity and potential rate capability. The charge integration method gave the highest figure of merit of 1.37 using a long window of 272.5 ns but had a γ-sensitivity of 2×10−6 which was poorer than the tail sum algorithm. The tail sum algorithm was able to achieve a figure of merit of 1.36 with a window of 250 ns and a γ-sensitivity on the order of 10−7. Reducing the integration windows to match the fastest algorithm of time to 10% resulted in the tail sum outperforming the other algorithms with a figure of merit of 1.26 and a γ-sensitivity of 6×10−7. The short charge integration method and tail-sum were compared on the EMMA beamline at the ISIS pulsed neutron and muon source. The tails sum demonstrated better separation between the γ-rays and thermal neutron at an incident peak neutron rate of 9.6×105 neutrons per second.

Multiple Hydrogen Bond-Induced Structural Distortion for Broadband White-Light Emission in Two-Dimensional Perovskites

Low-dimensional hybrid lead-halide perovskites with broadband white-light emission upon near-UV excitation have attracted immense scientific interest due to their potential application for the next...

Solution-processed all-inorganic perovskite CsPbBr3 thin films for optoelectronic application

The all-inorganic CsPbX3 (X=Br, Cl and I) perovskites have attracted considerate attention because of their potential and promising applications in optoelectronic devices. Herein, all-inorganic CsPbBr3 thin films were fabricated by a solution-processed synthesis at low temperature. For the photodetector fabrication, the all-inorganic perovskite films were utilized interdigital patterned gold electrodes and photoconductive detectors were obtained. The detailed structural properties showed that these as-prepared films were typical CsPbBr3 perovskite structure by X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) technique. The scanning electron microscopy (SEM) suggested that the surface of CsPbBr3 thin films was dense and smooth. And the as-fabricated films appeared photoluminescence emission at around 525 nm. Moreover, the as-constructed CsPbBr3-based photodetector exhibited faster photoresponse characteristics of short decay time (0.213 s) and rise time (0.233 s). As a key basis of merit, quick response speed is supposed to originate from the fast extraction and efficient generation of photoinduced charge carriers as well as small leakage current, which not only suggests that all-inorganic CsPbBr3 is a promising material for photodetector application, but also provides a low-cost and simple method for visible-light optoelectronic sensor application.

Tunable multicolor upconversion luminescence of Yb3+ sensitized Na3La(VO4)2 crystals

AbstractMulticolor upconversion luminescence materials show significantly applications in materials science. In this paper, the novel Yb3+‐sensitized Na3La(VO4)2 upconversion luminescence crystals are synthesized by the solid‐state reaction method. Three primary colors upconversion luminescence are successfully achieved in Na3La(VO4)2:Yb3+,Tm3+, Na3La(VO4)2:Yb3+,Er3+, and Na3La(VO4)2:Yb3+,Ho3+ crystals excited by the single 980 nm LD. Multicolor upconversion luminescence can be obtained by simply adjusting the combination ratios of these three samples. Luminescence mechanisms of the Yb3+‐sensitized system are discussed in detail. In the Na3La(VO4)2 host material, the Yb3+/Ho3+ codoped system exhibits unusual red upconversion luminescence based on the short decay time of Ho3+ ion 5I6 level, which provides the possibility of three primary color luminescence under 980 nm excitation.

Overview of S(T)EM electron detectors with garnet scintillators: Some potentials and limits.

The paper is focused on a complete configuration and design of a scintillation electron detector in scanning electron and/or scanning transmission electron microscopes (S(T)EM) with garnet scintillators. All processes related to the scintillator and light guide were analyzed. In more detail, excitation electron trajectories and absorbed energy distributions, efficiencies and kinetics of scintillators, as well as the influence of their anti-charging coatings and their substrates, assigned optical properties, and light guide efficiencies of different configurations were presented and discussed. The results indicate problems with low-energy detection below 1 keV when the scandium conductive coating with a thickness of only 3 nm must be used to allow electron penetration without significant losses. It was shown that the short rise and decay time and low afterglow of LuGdGaAG:Ce liquid-phase epitaxy garnet film scintillators guarantee a strong modulation transfer function of the entire imaging system resulting in a contrast transfer ability up to 0.6 lp/pixel. Small film scintillator thicknesses were found to be an advantage due to the low signal self-absorption. The optical absorption coefficients, refractive indices, and the mirror optical reflectance of materials involved in the light transport to the photomultiplier tube photocathode were investigated. The computer-optimized design SCIUNI application was used to configure the optimized light guide system. It was shown that nonoptimized edge-guided systems possess very poor light guiding efficiency as low as 1%, while even very complex optimized ones can achieve more than 20%.

Performance evaluation of YAlO3 scintillator plates with different Ce concentrations

Since Ce-doped YAlO3 (YAP(Ce)) scintillators have small non-proportionality, it is useful to develop a radiation imaging detector for low-energy gamma photons or X-rays. However, the YAP(Ce) performance with different Ce concentrations remains unclear. Consequently, we measured the basic performance of YAP(Ce) plates with different Ce concentrations. We used three types of YAP(Ce) scintillator plates with different Ce concentrations: 0.05% Ce, 1% Ce, and 2% Ce. The YAP(Ce) plates were 10 mm × 10 mm x 0.5 mm. We measured and compared the energy spectra, the decay times, the α-γ ratio, and the non-proportionality. We also evaluated the relation between these performances and the Ce concentrations. The light output of a YAP(Ce) showed positive correlation with the Ce concentrations, and the decay time of the YAP(Ce) showed a negative correlation with them. The energy resolution slightly improved for a YAP(Ce) with higher Ce concentrations. We found the α-γ ratio were slightly larger for higher Ce concentrations. The YAP(Ce) plate with a 2% Ce had the highest light output and the best energy resolution as well as the shortest decay time. Based on these results, the YAP(Ce) plate with a concentration of 2% Ce is a better selection for the development of radiation detectors or radiation imaging detectors for low-energy gamma photons or X-rays as well as alpha particles.

Red photoluminescence and purple color of naturally irradiated fluorite

Natural radiation-induced red fluorescence of fluorite consists of two broad bands at 750 and 635 nm with very short decay times of 20.3 and less than 5 ns, respectively. The first one is connected to an M center compensated by Na, while the second is connected to an M⁺ center, possibly formed as result of the M center’s destruction by UV irradiation. The optically active centers in naturally irradiated fluorite responsible for red luminescence and purple color are different from one another. The most probable reason for the purple color is colloidal calcium and not the M_(Na) center.

Facile fabrication of heterostructure with p-BiOCl nanoflakes and n-ZnO thin film for UV photodetectors

Herein, high-quality n-ZnO film layer on c-sapphire and well-crystallized tetragonal p-BiOCl nanoflakes on Cu foil are prepared, respectively. According to the absorption spectra, the bandgaps of n-ZnO and p-BiOCl are confirmed as ~3.3 and ~3.5 eV, respectively. Subsequently, a p-BiOCl/n-ZnO heterostructural photodetector is constructed after a facile mechanical bonding and post annealing process. At –5 V bias, the photocurrent of the device under 350 nm irradiation is ~800 times higher than that in dark, which indicates its strong UV light response characteristic. However, the on/off ratio of In–ZnO–In photodetector is ~20 and the Cu–BiOCl–Cu photodetector depicts very weak UV light response. The heterostructure device also shows a short decay time of 0.95 s, which is much shorter than those of the devices fabricated from pure ZnO thin film and BiOCl nanoflakes. The p-BiOCl/n-ZnO heterojunction photodetector provides a promising pathway to multifunctional UV photodetectors with fast response, high signal-to-noise ratio, and high selectivity.

Scintillation properties of Mn-doped methylammonium lead chloride crystals

Organic–inorganic perovskite materials with a bulk structure MAPbX3 (MA: methylamine, X: halogen) have attracted much attention in various applications such as solar cells, photodiodes, and radiation detectors. Herein, we synthesized (CH3NH3)Pb1-xMnxCl3 (or Mn-doped MAPbCl3) crystals by inverse temperature crystallization method to develop scintillator materials and evaluated their photoluminescence (PL) and scintillation properties systematically. The Mn-doped MAPbCl3 crystals showed a sharp emission peak at approximately 410–430 nm with short decay times on the order of nanoseconds and a broad peak at approximately 600 nm with a long decay time on the order of milliseconds in PL and scintillation. Furthermore, pulse height spectra of the Mn-doped MAPbCl3 crystals with a shaping time of 1 µs were measured, and the obtained scintillation light yields were estimated to be 66 (x = 1), 82 (x = 5), and 67 (x = 10) photons/5.5 MeV-α. Moreover, afterglow levels of the Mn-doped MAPbCl3 crystals were found to be 161 (x = 1), 264 (x = 5) and 170 (x = 10) ppm, which were comparable to a previously reported afterglow level of Tl-doped CsI.

Optical Properties of Thick Zinc Oxide Films Doped with Gallium and Gold

Samples of thick (30–32 µm) films of pure and gallium- and gold-doped zinc oxide obtained by magnetron sputtering using an uncooled target have been investigated. It is shown that the main changes in the optical properties of undoped thick ZnO films during recrystallization annealing under atmospheric conditions occur for the first 2–3 h. It is found that doping of thick ZnO films with gallium (4 at %) without additional heat treatment doubles the transmittance (to a value of about 97%). At the same time, this introduced gallium concentration leads to concentration quenching of X-ray luminescence. The results of measuring temporal characteristics show that the shapes of X-ray luminescence kinetics of samples with a gold buffer layer after heat treatment and undoped ZnO samples are identical and characterized by a long shoulder of slow luminescence with a characteristic time of about a microsecond and low integrated intensity with a short decay time.