Nature of the anomalies of the thermolumenescence properties of dosimetric α-Al2O3 crystals

The results of investigations into the anomalies of the thermoluminescence properties of dosimetric corundum crystals are presented. The decisive role of deep-lying traps in the quenching of luminescence in anion-defect Al₂O₃ monocrystals is shown. The existence of deep-lying traps is demonstrated by the method of direct observations of thermoluminescence (TL) peaks associated with them. Experimental evidence for the influence of the degree of occupation of deep-lying traps on the main features of the TL dosimetric peak at 450 K is given. The results obtained are interpreted for a model of the interactive system of traps, which differs radically from the models described in the literature by a consideration of the temperature dependence of the probability of trapping of charge carriers on deep-lying traps. We believe that the heat quenching of luminescence is due to the thermal ionization of excited F-center states. Ural State Technical University. Translated from Izvestiya Vysshikh Uchebhykh Zavedenii, Fizika, No. 3, pp. 55–65, March, 2000.     

Luminescent and dosimetric properties of nanostructured ceramics based on aluminum oxide

The main features of thermoluminescence (TL) of nanostructured ceramics based on anion-defective aluminum oxide have been investigated. The kinetic parameters of the TL dosimetric peak at 475 K have been determined. The possibility of using nanostructured ceramics for beta-radiation dosimetry of high doses (up to 1 kGy) with thermoluminescence of deep traps has been justified. It has been found that the light sum of the dosimetric peak decreases with an increase in the heating rate due to the temperature quenching of the luminescence. The obtained results have confirmed that the mechanism of TL quenching in anion-defective aluminum oxide is associated with the temperature dependence of the probability of the capture in deep traps, which can be caused by thermal ionization of excited states of F-centers.     

The impurity-induced luminescence of RbMnF3

The impurity-induced luminescence of RbMnF₃ has been studied in the temperature range, 4–120 K. Multimagnon sidebands of impurity-induced Mn²⁺ emission lines have been detected spanning the spectral range, 5515–5960 Å. The broad emission bands, which peak at 5750 Å and 6440 Å, have been attributed to phonon-assisted transitions from two impurity-induced Mn²⁺ traps of different depths. Pulsed luminescence measurements indicate that the quenching of the shallow trap emission is by a thermal activation to the E1 exciton level whereas the quenching of the deeper trap emission is by a multiple phonon decay. The coupling between Mn²⁺ ions is strong enough to support a detectable transfer of excitation between these two traps.The results of this research also include the observation in absorption of the E1 exciton line and its 1-magnon and possible 2-magnon sidebands.     

Porphyrin films — 5: Strong fluorescence

Films of tetra(perfluorophenyl)porphyrin (TFPP) show comparable strong host fluorescence whether deposited on room temperature or heated (135°C) mica substrates. Films of tetraphenylporphyrin (TPP) show only 9% as much fluorescence when deposited on unheated mica but 60% as much fluorescence when deposited on heated mica; moreover, the latter films show enhanced fluorescence from impurity guests. Octaethylporphyrin (OEP) behaves like tetraphenylporphyrin. It is observed that crystallite size is larger for films deposited on heated as compared to unheated mica. Larger crystallites could explain increased host and guest fluorescence in films of TPP and OEP prepared on heated substrates if grain boundaries serve as sites both for quenching and for trapping host excitons. The strong host fluorescence of films of TFPP can be explained either (a) by very slow exciton diffusion rates or (b) very few host quenching sites and very few guest trapping sites.     

GdVO4:Eu3+的热释光研究

GdVO4:Eu^3 有着十分优良的发光特性，它发光强度高，特别是具有很好的温度特性，在室温以上发光强度随温度的升高而增强，很利于在高温下使用此材料。本文对它的热释光进行了研究，其热释光峰值分别位于193，235和304K，根据计算可知它们的陷阱深度分别为0.39,0.47和0.61eV，陷阱的主要来源可能是F^ ,F和钒空位；Eu^3 掺入导致的晶格畸变，其中最主要的来源可能是空位导致的。     

Luminescence and energy transfer in TbAl3B4O12

An investigation of the luminescence properties of TbAl₃B₄O₁₂ in the temperature region 1.4–300 K is reported. Laser site-selection and time-resolution techniques were used.The results show that energy migration among Tb³⁺ ions on the regular crystallographic sites occurs. The transfer characteristics at room temperature are consistent with a diffusion-limited transfer process to Mo³⁺ quenching centres. The diffusion constant and the critical transfer distance for Tb³⁺ → Mo³⁺ transfer are derived. The rate of diffusion increases for decreasing temperature. At about 60 K a transition from diffusion-limited transfer to trapping-limited transfer occurs. This behaviour is due to the variation in the diffusion constant with temperature. In the temperature region below 60 K transfer to Tb³⁺ traps is observed. The intensity of the emission from the traps increases exponentially with decreasing temperature. However, the overall transfer rate to Mo³⁺ and traps remains roughly constant. A simple model including time-independent transfer rates and back transfer from traps to intrinsic Tb³⁺ ions is proposed to explain the results. The rates of transfer to Mo³⁺ and traps are obtained.     

Effects of annealing on TL sensitivity of granitic quartz

A TL sensitivity change can usually be observed after the quartz sample is heated to a high temperature. The change of 110°C TL peak or PTTL was reported to be an increase in many studies. The change of TL sensitivity of other TL peaks, mainly 150 and 375°C, with annealing treatments was demonstrated in this study. Two types of TL sensitivities in granitic quartz were found. One type is the low temperature TL sensitivity (<250°C) which increases with annealing time and temperature. Another type is the high temperature TL sensitivity (>250°C) which usually decreases after annealing. If the TL sensitivity is a measure of the population of associated TL traps, the trap population is a potential geochronometer to date a cooling age of a granite host.     

The effect of quenching from different temperatures on Bi0.88Sb0.12 alloy

Structural, thermal, resistive and magnetic properties of melt quenched Bi_0.88Sb_0.12 alloys are reported. The samples are heated at three different temperatures, followed by rapid quenching in liquid nitrogen. Large temperature difference between liquidus and solidus lines, led to microscopic in-homogeneity in the alloy. The effect of quenching from different temperatures in polycrystalline Bi_0.88Sb_0.12 alloy has been studied. The parameters such as strain, unit cell volume, and resistivity are found to increase with temperature. Thermal variation of resistivity depicts non-monotonic temperature dependence. The total negative susceptibility increases and band gap of semiconducting Bi_0.88Sb_0.12 samples decreases with increasing temperature.     

The effect of deformation and quenching temperature on the mechanism of decomposition in steel EI702

It is shown that the mechanism of decomposition in steel EI702 is determined by the quenching temperature and the degree of prior deformation. On aging after quenching from low temperatures or after heavy deformation, the principal mechanism of decomposition, in which the '-phase is formed, is discontinuous precipitation. However, on aging after quenching from high temperatures, the principal mechanism is continuous decomposition. It is found that discontinuous decomposition in steel E1702 is a very desirable process, since by accelerating aging it greatly increases the strength characteristics. The nature of the effect of the quenching temperature on the mechanism of decomposition in steel E1702 is discussed.     

Modeling the effects of interface traps on passive quenching of a Ge/Si geiger mode avalanche photodiode

The influence of interface donor and acceptor traps on the behavior of Ge/Si separate absorption, charge and multiplication Geiger mode avalanche photodiodes under passive quenching is modeled. The effects of different trap types on the quenching behavior are investigated in this paper for the first time. Our results show that trap type and trap density significantly influence the APD quenching time and ability to quench for a particular quenching resistor.     

Ignition and transient dynamics of sub-limit premixed flames in microchannels

We examine, via two-dimensional numerical simulation of a model system, some unsteady transient ignition scenarios and sustained oscillatory combustion modes that can occur in a single-pass, conductive channel, premixed microburner. These issues are relevant to the problem of ignition, evolution to stable combustion and the operational modes of microcombustors. First, we describe an unsteady ignition sequence that may occur when a single-pass microburner with initially cold walls has its exit walls heated and maintained at a fixed temperature. In particular, we demonstrate that as the heat from the exit walls propagates down the microburner walls, a reaction wave is driven rapidly down the channel towards the inlet via a sequence of oscillatory ignition and quenching transients. This scenario has been observed experimentally during the ignition of a single-pass microburner. Secondly, we show how an initial axial wall temperature gradient can lead to a variety of sustained combustion modes within the channel, including stable stationary flames, regimes of periodic motion involving quenching and re-ignition, regimes of regular oscillatory combustion, and regimes consisting of a combination of re-ignition/quenching events and regular oscillatory motions, all of which have been observed experimentally.     

Temperature-induced delocalization of excitations in GaAs/AlAs type-II superlattices

This paper describes investigations of the photoluminescence spectra of heterostructures containing short-period type-II GaAs/AlAs superlattices grown both within the regime where the heterojunction is smoothed, and in a regime where it is not smoothed, in the temperature range 10–40 K. A quantitative analysis of the experimental data shows that the quenching of exciton luninescence in the majority of cases is characterized by a single value of the activation energy E ₂=8±1 meV which coincides with the value of the binding energy of an X-Γ exciton. It is concluded that the primary reason for quenching in this temperature interval is thermal dissociation of the exciton into a pair of free carriers whose delocalization is accompanied by nonradiative recombination at traps. It is observed that smoothing the heterojunction leads to an increase in the probability of quenching by 1–2 orders of magnitude on the average. Fiz. Tverd. Tela (St. Petersburg) 40, 1140–1146 (June 1998)     

Effect of high-temperature annealing on the dielectric properties of PbTiO<Subscript>3</Subscript> crystals

The permittivity anomalies observed in PbTiO₃ in the range 20–300°C are assumed to be initiated by electron-induced polarization of the trap—electron dipoles with relaxation. The traps are lead and oxygen vacancies. Thermal quenching of the traps suppresses the anomalies.     

Luminescence properties of “relatively” trap-free crystals of anhydrous salts containing divalent manganese

Crystals of RbMnCl₃, Rb₂MnCl₄, CsMnCl₃, RbMnBr₃, CsMnBr₃ and CsMnI₃ which are grown from melts in contact with elemental manganese luminescence strongly throughout the 10K to 300K range. At room temperature the emission intensities from these crystals are larger by orders of magnitude than those observed from crystals of the same salts prepared without metallic manganese. Emission lifetime and intensity measurements made as a function of temperature are consistent with the view that the contact of the molten salt with metallic manganese during crystal growth yields materials which are relatively free of quenching traps. The effect appears to be quite general.     

Thermally stimulated luminescence and infrared studies of CaS : Bi,Tm phosphors

Calcium sulphide phosphors doped with bismuth and thulium are prepared from Indian minerals. The glow curves are recorded in the temperature range of 96–320 °K. The activation energies are determined by analyzing the glow peaks after thermal cleaning, using different methods. The results show that, in these phosphors, the electron traps responsible for thermoluminescence are present prior to irradiation. The infrared absorption spectra are recorded in the range of 4000-250 cm^-1. It is concluded that the traps are due to host lattice defects which may arise from S^-2 ion vacancies, created during phosphor preparation.     

Negative photoconductance in thin indium antimonide films

Negative photoconductance or optical quenching has been observed in thin InSb films, fabricated by vacuum evaporation on glass substrates. An electronic flash was used as the light source. The time constant of the photocurrent measured on several samples ranges from 30 sec to 3 min. Whereas bulktraps localised in the narrow band gap of InSb (0.18 eV) can hardly be responsible for the high time constants, it is believed that slow surface traps or traps inside an In₂O₃ layer, covering the InSb film, are responsible for the optical quenching.     

Thermally stimulated electron emission in the paraelectric phase of triglycine sulfate crystals heated at a high rate

Thermally stimulated electron emission is experimentally observed in ferroelectric triglycine sulfate (TGS) crystals in a temperature range whose upper limit is 10–15 K above the Curie point. Samples of a nominally pure and a chromium-doped TGS crystal, heated at different constant rates q=dT/dt, are investigated. It is shown that an increase in the heating rate results in increased emission current density over the entire temperature range investigated. The temperature at which emission arises depends only slightly on the rate q. At the same time, the temperature at which emission ceases increases monotonically with increasing q; if q is less than 1 K/min, this temperature is below the Curie point, while at q=4–5 K/min, this temperature becomes as large as 60–65°C, which is more than 15°C above the Curie point. In chromium-doped TGS crystal, the electron emission onset temperature is close to that of pure TGS, but the width of the temperature range over which emission is observed in the paraelectric phase is approximately two times less than in the case of pure TGS heated at the same rate. The emission disappearance below the Curie point (in the ferroelectric phase) at low q is explained as a result of full emptying of the electron traps under slow heating. The reason for the occurrence of emission above the Curie point is related to the charges that shield the spontaneous polarization and, because of their slow relaxation, persists in the paraelectric phase.     

Exciton spectra of layered PbI<Subscript>2</Subscript> and PbI<Subscript>2</Subscript>:Zr crystals

We have analyzed the surface morphology of single crystal samples of lead diiodide and studied the absorption edge and the temperature variation of their photoluminescence spectra. We have established that the zirconium impurity is uniformly incorporated into the crystal lattice of the samples and promotes appreciable quenching of photoluminescence due to formation of electron traps. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 252–257, March–April, 2007.     

Quenching of electroluminescence and charge trapping in high-efficiency Ge-implanted MOS light-emitting silicon diodes

Combined measurements of charge trapping and electroluminescence intensity as a function of injected charge and current have been carried out with the aim of clarifying the mechanisms of electroluminescence (EL) quenching in Ge-implanted ITO-SiO₂-Si light-emitting silicon diodes. Good correlation between the negative charge capture in traps of small effective capture cross-sections (σ_t1 ^e=1.7×10^-19 cm² and σ_t2 ^e=4.8×10^-20 cm²) located in SiO₂, and the quenching of the asymmetrical EL line with a maximum intensity at 400 nm has been observed. Similar correlation between the electron capture in traps with extremely small effective capture cross-section (σ_t3 ^e=5×10^-21 cm²) and the quenching of the EL line at 637 nm has been established. A quantitative model for the EL quenching has been developed, which takes into account the modification of the luminescent centers with subsequent electron capture at the newly generated traps. The model shows good agreement between simulation and experimental data. It also demonstrates that small effective capture cross-sections for electron charging during the EL quenching are determined by the probability of the luminescence centers (LCs) being disrupted, and enables one to estimate the Ge concentration associated with the EL at 400 nm. PACS 72.20.Jv; 73.40.Qv; 73.50.Gr     

Some luminescent properties of additively colored KBr · Ag crystals

The luminescent characteristics of additively colored KBr · Ag crystals are investigated. In particular, the decay of the phosphorescence, the flash of emission due to IR light in relation to the silver concentration, and the temperature quenching of the steady luminescence are discussed. It is shown that the investigated crystals have a complex system of shallow and deep traps. The thermal activation energy for nonradiative transitions in the B centers is found. It is concluded that the luminescence is produced by an electron-recombination mechanism.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 81–85, November, 1973.