Electroluminescence in In-ZnSe: Cu-ZnSe(s)-Au structures

The electroluminescent properties of In-ZnSe: Cu-ZnSe(s)-Au structures have been studied in the temperature range from 27 to 300 K. The spectrum of the forward-biased diodes at 27 K consists of emission lines due to the recombination of bound excitons, an associated donor-acceptor pair band with LO-phonon replicas and a deep level emission (green and red bands). At room temperature only the red band was observed. The time-resolved spectra (TRS) of the deep levels emission have also been investigated.     

X-ray and thermoluminescence of LiKB4O7 single crystals

The thermoluminescent (TL) and X-ray luminescent (XL) spectra of undoped LiKB₄O₇ (LKBO) single crystals had been investigated in the temperature range 80-300 K. It was found that in LKBO crystals, there are two intensive TL peaks at 112 and 132 K. The only one band emission spectra of sharply defined Gaussian shape, confirming the same mechanism of XL and TL by the radiation annihilation of the strongly localized self-trapped excitons (STE), had been observed in the TL and XL spectra. The possible models of these localization centers STE have been discussed.     

Temperature-dependent photoluminescence from bicrystalline ZnS (core/shell) nanocables

The experimental study of the temperature-dependent photoluminescence properties of bicrystalline ZnS core/shell nanocables under 10 K to 300 K was reported. The results show that there are two distinct peaks situated at the UV (about 372.6 nm) and green (about 500 nm) regions, respectively, and one blue-shoulder band (about 465 nm) superimposed between them for all spectra. The UV peak shows an obvious redshift with increasing temperature. The analyses of Gaussian-fitted the blue-shoulder band and the green bands from 10 K to 300 K reveal that all spectra can be well fitted by three Gaussian peaks: blue peak (B, about 2.67 eV), two green peaks (G1, about 2.47 eV and G2, about 2.42 eV). With increasing temperature, the blue band shows blueshift. The green bands show anomalous transition: green band G1 shows blueshift-redshift transition and green band G2 shows redshift-blueshift. The origins of these bands and their temperature-dependent shifts are explained based on defect levels and strong carrier localization effect at the defect levels in addition to band-gap shrinkage.     

Electronic absorption and emission spectra of Alq3 in solution with special attention to a delayed fluorescence

Tris(8-quinolinolato)aluminum(III) (Alq₃) shows electronic absorption bands at 378, 360 (in a 1:1 mixed solvent of methanol and ethanol (ME) at 77 K), 334, 316, 300, 263, 255.8, and 233 nm in ethanol at room temperature. According to the polarized fluorescence excitation spectrum together with MO calculations, for instance, the 360 nm band is assigned to an LL CT transition (an intramolecular charge transfer transition between two ligands), and the 378 nm band to an LM/ML CT one (an intramolecular charge transfer transition between ligand and metal). Alq₃ shows a broad fluorescence band peaking at around 478 nm in the ME matrix at 77 K. The emission spectrum measured with a phosphoroscope has two emission bands at 567 and 478 nm. The 567 nm band accompanies vibronic bands at 578 and 605 nm, being safely assigned to a phosphorescence of Alq₃. The lifetimes of the 478 and 567 nm bands are both 5.4 ms. The lifetime of the 478 nm band together with the band position and its band shape indicate that this band can be assigned to a delayed fluorescence.     

Photoluminescence excitation properties of porous silicon with and without Er-Yb-containing complex

Two bands in the photoluminescence excitation spectra have been studied for the red, blue, and IR emission of oxidized porous silicon (PS) and PS with Er³⁺- and Yb³⁺-containing gadolinium oxychloride complex (PS:Er,Yb), introduced by thermal diffusion. These two spectral bands were shown to reflect contributions of two different mechanisms of excitation-emission processes. The UV band for the IR emission of PS:Er,Yb rose sharply at about 290 nm and was explained by the direct photoemission of carriers from the valence band of Si crystallites into the conduction band of the oxide shell. The second band was found to be common for the red and blue emission and assosiated with the carriers photoexcitation inside the Si crystallites. Lifetimes for both bands were measured and the structure of the blue emission from PS:Er,Yb with peaks at 416, 440, 466, and 500 nm from PS:Er,Yb was observed.     

UV induced processes in pure and doped SrF2

The effects of UV irradiation on pure and Tb doped SrF₂ were investigated by TL methods, and compared to those of X irradiation. Excitation spectra were measured in the range 110–300 nm. In both the pure and doped samples excitation maxima appeared on the long wavelength tail of the first exciton band (at 125 nm), indicating an excitonic process for defect creation. The doped specimens showed additional maxima at lower energies, which were attributed to transfer of electrons to local impurity levels. Thermal activation energies were evaluated by various methods. TL emission spectra were also measured. The same spectral bands appeared in the glow peaks of SrF₂ : Tb after UV as after X irradiation. Results indicate that UV and X induced TL are due to similar processes.     

Injection of the edge electroluminescence in ZnSe MOS diodes

Injection luminescence and related properties of metal-ZnO-ZnSe-metal tunnel diodes are described. The edge emission of ZnSe is studied in the temperature range 30-300 K with respect to: a) band shape b) coupling strenght parameter, c) time resolved spectra and d) temperature dependence.External quantum efficiecies of the blue band of 2.61 × 10^-5 have been observed at 77 K. The lowest voltage threshold observed for blue band emission is 1.5 V.The relation between the electroluminescence and electrical characteristics of the MOS diodes are discussed.     

水热合成碳颗粒的结构和发光性能

用生物试剂氨基葡萄糖盐酸盐和葡萄糖在水溶液中合成了碳颗粒,用场发射扫描电子显微镜、高分辨透射电子显微镜、显微Raman光谱仪和傅立叶红外光谱仪对样品的结构和组成进行了研究。结果表明,碳颗粒是球形非晶结构,直径为0.3~1.4μm。利用He-Cd激光器的325 nm线,在显微Raman光谱仪中对碳颗粒的光致发光(PL)性能进行了研究。光谱显示出中心在420 nm的弱的蓝色PL带、中心在575 nm和650 nm的强而宽的绿光和红光PL带,它们分别与官能团和带与带之间的跃迁有关。绿光和红光PL带的宽化与sp2碳颗粒的非均匀性有关。     

Red emission of PbWO4 crystals

Luminescence characteristics of a large number of undoped and doped PbWO₄ crystals, grown by the Czochralski or Bridgman method, as-grown or annealed in the nitrogen atmosphere or in air, were studied in the 4.2–300 K temperature range. Two types of red emission centres were found. The centres with the emission band, peaking at 4.2 K at 1.57 eV, were observed in most of the crystals studied. The centres with the emission band, peaking at 4.2 K at 1.48 eV, were observed only in the PbWO₄ : Mo⁶⁺, Y³⁺ crystal. It is suggested that incompletely compensated lead vacancies are responsible for the appearance of the red emission.     

叶绿素A较高激发态的发光

采用激发样品表层和样品中心两种激发方式,在300K和77K温度下研究叶绿素A(Chla)的较高激发行为,观测到峰值位于493、520和580nm三条新的荧光发射带.分别测量它们的荧光激发光谱,证明这三条新的荧光带属于Chla的第二激发单线态向基态的不同振动能级的辐射跃迁发光.最后提出电子跃迁模型,同时进行了讨论.     

Comparison of blue and red TL from quartz

Following a suggestion by Scholefield and Prescott that blue and red emissions in quartz may involve the same electron traps, we have made a detailed study of blue and red TL glow peaks in some Australian sedimentary quartz samples (Scholefield, R.B., Prescott, J.R., 1999. The red thermoluminescence of quartz: 3-D spectral measurements. Radiat. Meas. 30, pp. 83–95). Allowing for thermal quenching of the blue TL, the Rapidly Bleaching Peak (at 325°C for a ramp rate of 20 K s⁻¹) and the low temperature peaks at 140–220°C appear to be identical in the blue and red. We conclude that the electron traps are the same, but that the blue and red luminescence centers probably do not occur in the same grains. On present evidence we cannot determine whether or not the Slowly Bleaching Peak (at 375°C for 20 K s⁻¹) involves the same traps in the blue as in the red. As did Scholefield and Prescott, we find no evidence of a red peak at 100°C.     

Tunnel afterglow, fading and infrared emission in thermoluminescence of feldspars

Anomalous fading of TL, OSL and IRSL has been observed in many samples of feldspars and attributed to the tunnel effect. Investigations do show expected tunnel afterglow except for samples with no fading. Its intensitym quite noticeable at LNT, is in proportion with reported rate of fading. The emission is entirely in the red and infrared part of the spectrum. An important thermal quenching is observed. Low temperature storage results in fading of TL. Cathodoluminescence emission spectra, monitored from 200 to 900 nm, do confirm TL observations. They show two well-separated ranges: one, “blue”, from UV to yellow (the only one observed in usual TL dating), displays various emission bands; the other, “IR”, red and infrared, shows a well-characterized narrow Gaussian emission band, with a maximum around 720 nm. Models are proposed, relating fading with disorder in crystals. Tunnel afterglow appears as a good criterion of fading in feldspars.     

Investigation of emission properties of Tm3＋：Y2O3 transparent ceramic

A transparent and emitting ceramic of Y 2 O 3 doped with 6% Tm 3+ ions is fabricated by vacuum sintering with ZrO 2 . Absorption, photoluminescence (PL), and PL excitation (PLE) spectra are investigated in a spectral range of 200 to 2 100 nm at various temperatures between 296 and 12 K. Intense emission band appears at 450 to 465 nm in the visible range. Near-infrared emission bands are observed at 1 200 to 1 300 nm and 1 400 to 1 550 nm, with intense peaks at 1 270, 1 450, and 1 523 nm. The luminescence mechanisms and potential applications of the emissions are discussed with the help of Judd-Ofelt theory and PLE spectra.     

Dose response of thermoluminescence emission spectra of LiF:Mg,Ti with different Mg, Ti impurity concentrations

The dose response of the TL emission spectra of an LiF:Mg,Ti (TLD-100) sample and three LiF:Mg,Ti samples with different impurity concentrations (0–6 ppm Ti and 80–100 ppm Mg) have been measured. At a dose less than 22 Gy the emission spectrum of the TLD-100 sample comprises one emission band at 420 nm. The sample without Ti shows also one emission band but now at 620 nm. The spectra of the other two samples comprises two emission bands at 420 nm and 620 nm of which the intensity of the 420 nm band increases with increasing Ti concentration. The dose response of the glow peaks is different for peaks at different temperatures and emission bands. From these observations it can be concluded than in LiF:Mg,Ti at least some of the traps and luminescent centers are coupled.     

Spectral characteristic of high-dose high-temperature emission from LiF:Mg,Cu,P (MCP-N) TL detectors

High-temperature emission spectra of LiF:Mg,Cu,P (MCP-N) TL detectors, irradiated above the nominal saturation level, up to the hundreds of kGy, have been measured. Emission spectra integrated over the whole temperature range, as well as the spectra recorded at the temperatures corresponding to the TL peaks maxima, were analyzed. With increasing dose of γ-radiation no significant changes were observed in the short wavelength emission range (220–450 nm) of the measured spectra. For doses of 4 kGy and higher the long wavelength emission (450–800 nm) started to be visible. All recorded spectra have been expressed in a form of the sum of several Gaussian-shape bands in the energy domain, which parameters remain in a general agreement with the measurements of Mandowska et al. (2010). Spectra of the low-temperature, main, high-temperature and “B” TL peaks were investigated. In the ranges of the low-temperature and the main dosimetric peaks, that is 100–125 and 210–230 °C, respectively, the short wavelength emission disappeared with increasing dose and for the highest doses the long wavelength emission became dominant. Both the high-temperature (290–320 °C) and the “B” (370–425 °C) peaks emission spectra exhibited somewhat different behavior with increasing dose. Initially, an even growth of the whole spectrum was observed and for doses higher than 16 kGy the intensity of the spectrum decreased, but the short wavelength emission band fell significantly faster, in case of the high-temperature TL peaks. In case of the “B” peak emission spectra the long wavelength emission did not play any role in the analyzed dose range. The spectra measured at the TL peaks maxima were also fitted with several Gaussian-shape bands. Dose-intensity dependences for all Gaussian-shape bands fitted to the measured spectra are also included in this paper.     

Luminescence and relaxed excited state origin in CsI:Pb crystals

Emission and excitation spectra, luminescence polarization and decay kinetics have been studied for CsI:Pb crystals in the 0.36-300 K temperature range. The origin of the excited states responsible for the optical characteristics has been discussed. It has been concluded that the doublet ≈3.70 eV absorption (excitation) band is caused by the electronic transitions into the Pb²⁺ triplet state split due to the presence of a cation vacancy near a Pb²⁺ ion, while the higher-energy bands are of the charge-transfer origin. Like in CsI:Tl, four emission bands of CsI:Pb have been found to belong to the main luminescence centres. Two emission bands, peaking at 3.1 and 2.6 eV, are suggested to arise from the triplet relaxed excited state of a Pb²⁺ ion. Two visible emission bands, peaking at 2.58 and 2.23 eV, are interpreted as the luminescence of an exciton localized near the Pb²⁺ ion.     

纯绿LED的辐射机理和深能级研究

本文结合N-free GaP材料外延生长和器件研制,用时间分辨光谱和发射光谱对温度的依赖关系,研究了构成绿色辐射的不同跃迁过程,测量了它们的光生载流子寿命.通过阴极射线轰击芯片前后深能级瞬态谱(DLTS)的分析,并根据退化过程中近红外光谱的变化,探讨了影响纯绿LED效率的主要因素.     

Strong violet luminescence from ZnO nanocrystals grown by the low-temperature chemical solution deposition

The luminescence properties of zinc oxide (ZnO) nanocrystals grown from solution are reported. The ZnO nanocrystals were characterized by scanning electron microscopy, X-ray diffraction, cathodo- and photoluminescence (PL) spectroscopy. The ZnO nanocrystals have the same regular cone form with the average sizes of 100-500 nm. Apart from the near-band-edge emission around 381 nm and a weak yellow-orange band around 560-580 nm at 300 K, the PL spectra of the as-prepared ZnO nanocrystals under high-power laser excitation also showed a strong defect-induced violet emission peak in the range of 400 nm. The violet band intensity exhibits superlinear excitation power dependence while the UV emission intensity is saturated at high excitation laser power. With temperature raising the violet peak redshifts and its intensity increases displaying unconventional negative thermal quenching behavior, whereas intensity of the UV and yellow-orange bands decreases. The origin of the observed emission bands is discussed.     

Colour centres in powdered KI

Fine powder of KI was coloured in an electrodeless discharge. Due to quick bleaching of the F centres produced in this method, it was possible to prepare the samples that were almost free from the F centres. High concentration of the electron deficient centres could be produced, which were studied by measuring the diffused reflectance. A band at 354 nm is shown to be composed of two overlapping bands. Further, growth of a band appearing at 265 nm is studied. Bleaching characteristics of the samples are studied and it is shown that, similar to F centre bleaching, bleaching of these samples also proceeds in at least two steps. The difference between two components of the bleaching curves is quite marked. Further it is showed that the components are related to the presence of different absorption bands and appear at different stages of colouration.     

Investigation of thermoluminescence in Li_2B_4O_7 phosphors doped with Cu, Ag and Mg

Li_2B_4O_7 (LBO):Cu,Ag,Mg phosphors have been prepared by the sintering technique. The roles of the Ag and Mg dopants in the phosphors have been studied using the methods of thermoluminescence (TL) glow curves and TL 3D spectra. The results indicated that proper concentrations of Ag and Mg can enhance the TL of LBO:Cu. It was also indicated that the intensity of TL peak at ~130℃ is reduced with the in- creasing Ag concentration, and enhanced with the increasing Mg concentration. From the TL 3D spectra, three emission bands (λ1 = 421 nm, λ2 = 380 nm, λ3 = 350 nm) were observed: the intensity of low energy emission band is reduced and that of the high energy is enhanced with the increasing dopant Ag; on the contrary, the intensity of low energy emission band is enhanced and that of the high energy one is reduced with the increasing dopant Mg.