Optical properties of bismuth-doped TlCdCl<Subscript>3</Subscript> crystal

IR photoluminescence of bismuth-doped ternary thallium chloride TlCdCl₃ was studied. Two bismuth-containing luminescence impurity centers were detected. One of these was found to be the bismuth Bi⁺ monocation, emitting at 1025 nm.     

Study of the spectral properties of alkali halide electroluminescence with plasma electrodes

A method is given for separating the electroluminescence (EL) spectrum of alkali halide crystals (AHC) from the emission from plasma electrodes. Results are given for experimental studies of EL in AHC with electrodes in the form of a low-pressure plasma over a broad temperature range (from room temperature to 120 K) and electric fields up to 10⁹ V/m. The importance of the effect of defect formation processes on the structure of luminescent centers and the quantum yield of EL in AHC is shown. A mechanism is proposed for formation of the luminescent centers in AHC in a very strong electric field. Control Systems and Radio Electronics, Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fiziaa, No. 9, pp. 102–106, September, 1997.     

Unlocking The Inherent Luminescence of Eu2+/Eu3+ by Light-Induced Oxidation for Invisible Optical Storage

Color-tunable luminescent materials are increasingly recognized for their potential applications in high-security anticounterfeiting and optical storage technologies. However, luminescent materials with high-contrast photoswitching behavior that change their luminescence properties in response to external stimuli are extremely scarce. In this study, a time-dependent color-tunable luminescent material, Na₂BaSiO₄:Eu²⁺ (NBSO:Eu), is introduced. This material leverages the inherent luminescence of Eu²⁺/Eu³⁺ through a light stimulus. Under 365 nm irradiation, the blue luminescence of Eu²⁺ gradually degraded over time, reaching a luminescence contrast of up to 88%. This degradation is accompanied by a color change of the emitted light from blue to red (Eu³⁺). These color changes can be reversibly tuned by alternating light or thermal stimuli. Experimental investigations revealed that the photogenerated Eu³⁺ ions and defects, acting as killer centers, induced multicolor luminescent switching behavior. Owing to their unique optical properties, NBSO:Eu offers exciting opportunities for designing advanced dynamic anticounterfeiting and invisible optical storage.     

Highly enhanced luminescence of ZnO green phosphors by calcining ZnS with NH4Br as additive

Zinc oxide (ZnO) phosphors with highly efficient green emission have been prepared by calcining ZnS with NH₄Br as additive in air atmosphere. The luminescent properties of as-prepared ZnO phosphors were characterized by X-ray photoelectron spectroscopy and photoluminescence. Our results reveal that the green emission is ascribed to a transition of a photo-generated electron from the localized defect centers (V_o⁺) to a deeply trapped hole (V_Zn⁻) within the band gap. The addition of NH₄Br enhances the luminescent emission of ZnO by promoting the formation of vacancies of both oxygen and zinc.     

Defect evolution and photoluminescence in anion-defective alumina single crystals exposed to high doses of gamma-rays

A method of luminescent UV and VUV spectroscopy was used to study the evolution of color centers in anion-defective alumina single crystals exposed to high doses of gamma-radiation. A sharp drop in the intensity of the emission bands and, therefore, the concentration of F⁺ and F-centers associated with the formation of aggregate F₂-type centers was found. The aggregate centers create an additional emission band in the range of (1.8–2.8) eV. When the crystals are exposed to middle and high doses, the photoluminescence (PL) intensity is the highest in the emission band of F₂²⁺-centers, which indicates a high concentration of the aggregates from singly charged oxygen vacancies (of F⁺-centers). When PL of the crystals exposed to high doses is excited with synchrotron radiation of the VUV range, a wide emission band in the red and near infrared (NIR) regions is registered. The centers related presumably to impurity defects, their aggregates and clusters consisting of several oxygen vacancies are responsible for this emission band.     

Fluorescence properties of Bi4Ge3O12(BGO) single crystals under laser excitation: Excited state dynamics and saturation effects

Laser-excited techniques were used to investigate the optical properties of bismuth germanate crystals. Absorption, reflectivity, excitation, emission, lifetime, time-resolved fluorescence, photoconductivity, thermally stimulated conductivity measurements were performed at various temperatures on single crystals of different origins.The absorption is shown to occur in bismuth and germanate centers while both intrinsic and perturbed Bi³⁺ ions together with impurities contribute to the total fluorescence.The emission mechanism at room temperature involves a thermally activated energy migration, and at low temperature localized emitting centers. Formation of deep holes in the wide emission band at room temperature reveals saturation effects on various luminescent centers, promoted by energy migration. Trapped exciton models are proposed to explain the excited state dynamics occurring at low and room temperature.     

Investigation of Multicomponent Bismuth-Containing Heterostructures Based on A 3 B 5 Compounds

The results of a complex investigation of the multicomponent heterostructures based on the A ³ B ⁵ compounds are presented by the example of bismuth-containing solid solutions. The investigation was performed using the Auger electron and X-ray photoelectron spectroscopy. The component profiles in the structures are obtained. The properties and prospects of these compounds are described.     

Confocal Raman spectromicroscopy for tin-core/carbon-shell nanowire heterostructure

High density heterostructures of carbon nanotubes encapsulated single crystalline tin nanowires have been characterized by Raman spectromicroscopy. The morphology, composition and structure of the synthesized nanoheterostructures were examined by using scanning electron microscopy, transmission electron microscopy. The Raman spectra obviously manifest the crystalline nano-graphite within amorphous carbon walls in the heterostructures. The Raman image reproduces the pristine heterostructures of the CNTs as seen in SEM image, which illustrate the single nanowires oriented uniformly grown on micro-graphitic fibers. It was found that the resultant heterostructures are luminescent which was attributed to crystalline nano-graphite embedded in the amorphous carbon matrix, which is a consequence of excitons localization within an increasing number of sp² rich clusters. The contrast in the Raman image reflects nonuniform distribution of the graphite cluster size which acts as the radiative centers. The luminescent property was reviewed. The enhanced Raman spectra and luminescent property by the well-defined tin nanowires inside the heterostructures was revealed.     

Effects of dopant concentrations on phosphorescence properties of Eu/Dy-doped Sr3MgSi2O8

Long afterglow Sr₃MgSi₂O₈: Eu, Dy phosphor with high brightness was prepared by sintering at high temperature and weak reductive atmosphere. The luminescent properties of this photoluminescent pigment were studied systematically by investigating concentration effects. The analytical results indicated that the main emission peaks appear at 482 nm. The excitation and emission spectra of this phosphor show that both of them are broadband. This is ascribed to the 4f⁷→4f⁶5d¹ transition of Eu²⁺ in the pigment matrix, which is in good agreement with the calculated value of 470 nm, and implies that luminescent centers Eu²⁺ occupy the deca-coordinated Sr²⁺ sites with the host of Sr₃MgSi₂O₈.     

Photoluminescence properties of anodic alumina membranes with ordered nanopore arrays

Photoluminescence (PL) of anodic alumina membranes (AAMs) with ordered nanopore arrays fabricated in oxalic acid has been investigated under different annealing temperatures. The PL intensity firstly increases, and at 500 °C reaches a maximum value, then decreases. The structural transition from amorphous to γ-Al₂O₃ in AAMs has been confirmed by X-ray diffraction. Thermogravimetric analysis results and electron paramagnetic resonance measurements revealed that the PL band of alumina membranes could be attributed to the oxygen-related defect centers (F⁺ centers) rather than the luminescent centers transformed from oxalic impurities.     

Radio and thermoluminescence studies in CsI doped with F centers

Radioluminescence, thermoluminescence and u.v. excitation measurements in CsI additively colored crystals show a new luminescent component located at 2.5 eV. This is attributed to the radiative recombination of V_k centers with F centers. Another new component at 2.72 eV is observed only under u.v. excitation of 5.14 eV. This is related to the radiative recombination of localised excitons at F⁺ center sites (α band).     

掺稀土元素Dy和Mn,P,Cu的MgSO4的热释发光光谱

实验测定了MgSO₄:Dy,Mn和MgSO₄:Dy,P以及MgSO₄:Dy,P ,Cu等的热释光磷光体的三维发光谱.结果表明,掺入Dy的MgSO₄磷光体的热释发 光谱线的波长与Dy³⁺离子的能级跃迁相关,Dy³⁺为热释光主要发光 中心.MgSO₄中只掺入Mn时,温度在140℃和190℃附近呈现波长为660nm宽范围的 连续发光带,这是Mn形成的发光中心的 关键词： 热释发光光谱 稀土元素镝 硫酸镁     

Spectral-kinetic studies of SrAlF5 doped by trivalent rare-earth ions

Photochemical properties of Ce³⁺:SrAlF₅ and Ce³⁺,Yb³⁺:SrAlF₅ single crystals together with spectroscopic and kinetic characteristics of several optically nonequivalent impurity centers and energy transfer between them are described. It is shown that co-activation by Yb³⁺ ions effectively suppresses color centers in Ce,Yb:SAF crystals. It was found out that in Ce,Yb:SAF crystals Yb ions exist simultaneously in 2+ and 3+ valent state. Three types of optically nonequivalent luminescent centers corresponding to the doublets in luminescence spectrum centered at 290, 305 and 370 nm (Ce^I, Ce^II, Ce^III, respectively) have been observed. Analysis of luminescence spectra and decays leads to the conclusion that there is no energy transfer between either cerium centers or from Ce³⁺ to Yb²⁺ apart from the Ce^III center which luminescence is slightly quenched by Yb²⁺.     

Formation and stabilization of F centers following direct generation of self-trapped excitons in KCl crystals

The spectrum of luminescent F centers generated in high-purity KCl crystals by 7–10.2-eV photons has been measured at 230 K. The pulsed annealing of these centers (250–550 K), as well as the dependence of the efficiency of stable F-center generation on irradiation temperature (80–500 K) has been studied. The efficiencies of F ⁻ and Cl ₃ ⁻ -center generation are maximum under direct optical creation of self-trapped excitons in the region of the Urbach intrinsicabsorption tail. Besides the exciton decay with formation of F centers and mobile H centers, a high-temperature exciton decay channel which involves creation of cation defects stabilizing the H centers has been revealed. Fiz. Tverd. Tela (St. Petersburg) 41, 433–441 (March 1999)     

Eu2+激活的Ca3SiO5绿色荧光粉的制备和发光特性研究

研究了Eu²⁺激活的绿色发光材料Ca₃SiO₅的制备条件和发光性质. Eu²⁺中心形成主峰值为501 nm和次峰值为570 nm的特征宽带，两峰值叠加形成发射峰值为502nm的绿色发射光谱带. 利用这些光谱结果和Van Uitert 经验公式，确认Ca₃SiO₅:Eu²⁺中存在两种性质有差异的Eu²⁺发光中心，它们分别占据基质中八配位的Ca²⁺(Ⅰ)格位和四配位的Ca²⁺(Ⅱ)格位. 其激发光谱分布在250—450 nm的波长范围，峰值位于375 nm处，可以被InGaN管芯产生的350—410 nm辐射有效激发. 关键词： 发光 荧光粉 绿色荧光粉 3SiO₅')" href="#">Ca₃SiO₅ 2+')" href="#">Eu²⁺     

Mechanism of photostimulated luminescence: BaFCl:Eu2+

We propose a new parallel model based on the analysis of photostimulated luminescence (PSL) process and existing theoretical models. While solving this model, the general expression for PSL is gained. BaFCl:Eu²⁺, one of the PSL materials, is prepared and a series of spectra are measured. We compared the theoretical and experimental results in terms of the decay process, the difference between two kinds of color centers and the relationship between irradiation dose and luminescent intensity. Supported by the National Nature Science Foundation of China.     

Luminescent and photochemical processes in CdBr<Subscript>2</Subscript> : AgCl crystals

This paper reports on the results of the investigation into the optical luminescence properties of photochromic crystals CdBr₂ : AgCl grown by the Bridgman-Stockbarger method. It has been shown that, under X-ray, optical, and N₂-laser excitations of the grown crystals, there occurs emission due to Ag⁺ impurities in addition to emission from centers characteristic of CdBr₂. The photostimulated chemical reactions occurring in CdBr₂ : AgCl lead to a weakening of the luminescence and to a change in its spectral composition. Models of photosensitive centers and centers of photochemical coloring have been proposed. The mechanisms of the photochromic effect have been considered. The nature of luminescent and trapping centers has been discussed.     

Electronic structure of (Ag+)2 pairs in NaCl: A theoretical approach

MSXα calculations on double octahedral clusters Ag₂Cl₁₀⁸⁻ or Ag₂Cl₁₁⁹⁻ have been performed in order to depict (Ag⁺)₂ luminescent dimeric centers in NaCl. The effects of symmetry, bond lengths and Madelung potentials are discussed with regard to experimental results.     

Radiative relaxation of low-energy electron excitations and point defects in beryllium oxide

The mechanism by which elementary point defects arise and evolve in beryllium oxide crystals and the latest advances in the dynamics of electron excitations of this compound are considered. Experimental and theoretical results which touch on the generation and evolution of elementary point defects are obtained. The properties of intrinsic and impurity point defects, and the crystal-chemical fundamentals of defect generation, optical and luminescent transitions in them, and color centers are discussed. The electron structure of B²⁺, Al²⁺, Zn⁺, and [Li]⁰ defects, nonisothermal relaxation of paramagnetic centers, thermostimulated recombination processes, and the concept of the coexistence of two types of self-localized excitons in beryllium oxide, radiative annihilation of which gives rise to luminescence in the UV and far UV bands are considered. Ural State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 76–93, November, 1996.     

Stabilization of Eu2+ in KLuS2 crystalline host: an EPR and optical study

Electron paramagnetic resonance and luminescence spectroscopies were applied to study the incorporation and charge stability of Eu²⁺ luminescent ions in single crystals of KLuS₂:Eu found in an earlier optical study [Jary et al., Chem. Phys. Lett. 574 , 61 (2013)]. The location of Eu²⁺ in the structure was unambiguously determined and three different centers were identified and described. Two of these centers correspond to substitution of Eu²⁺ for K⁺ and Lu³⁺ ions providing thus effective mechanism for Eu²⁺ incorporation due to the charge self‐compensation in the lattice. The observed luminescence spectra are consistent with the results of electron paramagnetic resonance experiment and can be decomposed accordingly. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)