Photoluminescence and EPR studies on gamma irradiated Ce doped potassium halide single crystals

Electron Paramagnetic Resonance(EPR), Photoluminescence(PL), Thermoluminescence (TL) and other optical studies of γ-irradiated KBr, KCl:Ce³⁺ single crystals. Cerium when doped into the KBr, KCl is found to enter the host lattice in its trivalent state and act as electron trap during γ-irradiation, thereby partially converting itself to Ce²⁺. The Photoluminescence(PL) spectra of both KCl and KBr crystals doped with Ce exhibit the strong blue emissions of Ce corresponding to ⁵d(²D)→²F_5/2 and ⁵d(²D)→²F_7/2 transitions. The defect centers formed in the Ce³⁺ doped KBr and KCl. Crystals are studied using the technique of EPR. A dominant TL glow peak at 374, 422 K and KCl:Ce³⁺ at 466, 475 K is observed in the crystal. EPR studies indicate the presence at two centers at room temperature. Spectral distribution under the thermoluminescence emission(TLE) and optically stimulated emission(OSL) support the idea that defect annihilation process to be due to thermal release of F electron in KBr, KCl:Ce³⁺ crystals. Both Ce³⁺ and Ce²⁺ emissions were observed in the thermoluminescence emission of the crystals.     

Photoluminescence, optical absorption and XRD studies on X-ray irradiated terbium doped KBr crystals

This paper reports the optical absorption, photoluminescence (PL), XRD, SEM studies made on KBr:Tb³⁺ crystals. The integrated light intensity is enhanced by about two orders of magnitude as compared to the undoped samples in spite of some OH^- present in the samples. PL of these crystals exhibits characteristic Tb³⁺ emissions due to transitions from the ⁵D₃ to ⁵D₄ levels to various levels of the ⁷F septet on F-bleaching X-ray irradiated crystals Z₃ centers are observed. The bands observed in the emission spectra of Tb³⁺ doped KBr are found to be shifted to higher wavelength. The stokes-shift of KBr:Tb³⁺ is determined and it is found to have a large value. The XRD studies have been made to determine the crystalline structure of KBr and KBr:Tb³⁺ and also the Miller indices. The SEM studies made reveal the presence of microcrystalline structure.     

紫外线激发后KCl:Cu+的光激励发光

用固相反应法制备了KCl：Cu^＋多晶样品。经紫外光辐照后，用560nm的光照射能产生近紫外蓝光的光激励发光。研究表明，Cu^＋作为发光中心，经紫外光辐照后并没有产生Cu^＋到Cu^＋的变价，即Cu^＋不是空穴俘获中心，而阴离子空位充当电子陷阱。当激发后的样品受到光激励时，电子与空穴中心或Vk心复合后将能量传递给Cu^＋离子，产生d-s跃迁的特征发射。     

Optical study of Ce ion in gamma-irradiated binary barium-borate glasses

Absorption spectra measurements of cerium-doped binary system from barium-borate glasses have been measured. The effects of dopant concentration of CeO₂ and Al₂O₃ in the concentration range 0.54-2.9 and 4.8-9.2 mol%, respectively, and exposed to different irradiation doses have been measured in the range 1-7 eV and the result have been interpreted in terms of structural concepts. The radiation-induced broad band at 2.25-1.88 eV in the base glass is observed to be suppressed by the presence of cerium due to the transformation of Ce⁴⁺ to Ce³⁺. The released electrons are then used to annihilate positive holes responsible for this band. The resolution of the observed absorption spectra show two to seven induced bands depending on the glass composition. Absorption spectra of the irradiated binary glass system are found to be controlled by the cerium concentration. From the absorption edge studies, the values of optical band gap E_opt and Urbach energy ΔE have been evaluated. The oxidoreduction (redox) reaction Ce³⁺/Ce⁴⁺ is assumed to be related to the glass basicity and the possible complex-ion formation. The oxygen ion activity (O²⁻) is believed to be related to the basicity and to the possible oxygen ion formation in the glass melt, and the redox equilibrium is shifted toward the reduced state.     

Absorption Spectrum Study on Colloidal Centers in KCl:NCO:K

The absorption spectrum study on metallic colloidal centers in KCl:NCO:K crystals have been performed as a function of annealing temperature in the temperature range of 500–750K. Conversion process between F-centers and colloidal centers was observed and it is found that the NCO ions play an important role in the formation and stability of aggregative centers in alkali halides.     

Comparative investigations of TL and OSL in KCI:Eu2+ crystals irradiated with UV and X-rays

Abstract

We present thermoluminescence (TL) glow curves and optical stimulated luminescence (OSL) response from both KCl:Eu²⁺ crystals irradiated with soft X-rays (20 KV, 80 μA) and ultraviolet light (230 nm). Two situations take place. First, we observed that for long time F-light bleaching (560 nm) the typical TL glow curve of X-rays irradiated KCl:Eu²⁺ resembles the TL glow curve of UV-irradiated samples. Second, along with OSL measurements, we have performed a thermal bleaching and we have addressed F and F_z participation in OSL. These results provide us a supportable correlation between F and F_z as responsible centers for OSL and TL processes.     

Thermoluminescence and photoluminescence studies on gamma irradiated CsI: Pb2+ crystals

Pure and Pb²⁺-doped CsI crystals have been grown by the Bridgemann technique. Optical absorption, thermoluminescence (TL) and photoluminescence (PL) measurements have been performed. In undoped and Pb²⁺-doped cesium iodide crystals, F-centers and V-centers have been produced at 770 nm and 350 nm, respectively. In Pb²⁺-doped crystals, additional centers at 373 nm, 290 nm and 258 nm bands have been produced. In undoped samples, only two glow peaks at 343 K and 373 K have been produced, and in Pb²⁺-doped samples additional glow peaks at 383 K and 423 K have been produced. For all the samples, TL emission, PL and excitation measurements have been performed.     

Plasma resonance of granular indium films deposited on rough surfaces of NaCl and KCl single crystals

Granular films whose bands of plasma resonance are anisotropic are obtained by vacuum deposition of indium on rough surfaces of NaCl and KCl single crystals. On electron-microscopic pictures of samples, sections whose granules form chains with distances between them somewhat larger than the distances between the ganules in the chains are found. The maximum of the absorption band in polarized light along the chains is shifted into the low-frequency region of the spectrum in comparison to the abosorption band’s maximum in polarized light perpendicular to the chains. A second band of plasma resonance whose frequency is equal to the free-running frequency of electrons in a granule is found in the high-frequency region of the spectrum. Kharkov State University, 4, Svoboda Ave., 310077, Kharkov, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 799–803, September–October, 1998.     

Luminescence studies on SrMgAl10O17:Eu, Dy phosphor crystals

Using urea as fuel, SrMgAl₁₀O₁₇:Eu, Dy phosphor was prepared by a combustion method. Its luminescence properties under ultraviolet (UV) excitation were investigated. Pure SrMgAl₁₀O₁₇ phase was formed by urea-nitrate solution combustion synthesis at 550 °C. The results indicated that the emission spectra of SrMgAl₁₀O₁₇:Eu, Dy has one main peak at 460 nm and one shoulder peak near 516 nm, which are ascribed to two different types of luminescent Eu²⁺ centers existing in the SrMgAl₁₀O₁₇ matrix crystal. The blue luminescence emission of SrMgAl₁₀O₁₇:Eu phosphors was improved under UV excitation by codoping Dy³⁺ ions. The SrMgAl₁₀O₁₇:Eu phosphors showed green afterglow (λ=516 nm) when Dy³⁺ ions were doped. Dy³⁺ ions not only successfully play the role of sensitizer for energy transfer in the system, but also act as trap levels and capture the free holes in the spinel blocks.     

Luminescence and lifetime characteristics of microphases in KCl:KI:Pb mixed crystals

Absorption and luminiscence measurements were performed on lead-doped KCl:KI mixed single crystals. Strong differences were found between as-grown and quenched samples. New bands were observed in the absorption spectra of unquenched samples in the spectral region between the limit positions of the A bands, corresponding to chloride or iodide lattices. The strong band at 449 nm dominates the luminescence of these samples at low temperatures. Its kinetics have a complicated form and the decay time is in the interval from ns to ms. Quenched samples have a well-known luminescence spectrum caused by octahedral lead impurity centres in KCl single crystals. The kinetics, however, also indicate mixed chlorine and iodine coordination of lead in the investigated crystals.     

Defect states in Lu 3 Al 5 O 12 :Ce crystals

Wavelength-resolved TSL measurements after x-ray irradiation at room temperature were performed on undoped, Ce- and (Ce, Zr)-doped Lu 3 Al 5 O 12 crystals. Several glow peaks were observed in the 20-450 v C temperature region, whose intensities and emission spectra are influenced by doping. Namely, the TSL spectra are governed by defect and trace impurity-related emissions in the undoped crystal, while only the Ce 3+ emission is detected in the doped crystals. Moreover, EPR measurements performed at 12 v K revealed typical spectra of Ce 3+ (4f 1 , S =1/2) occupying Lu 3+ substitutional positions. In situ light irradiation (250-330 v nm) of the crystals results in a step-like decrease of the Ce 3+ EPR intensity. Such a behaviour can reflect a creation of Ce 4+ ions under UV irradiation or an increase of the Ce 3+ population in the excited (5d) state.     

Luminescence studies of thallium co-doped KBr:Eu2+ powder phosphors

In this study, photoluminescence (PL) and photostimulated luminescence (PSL) properties in KBr:Eu²⁺, Tl⁺ powder phosphors are reported. PL emission spectra of these Tl⁺ co-doped KBr:Eu²⁺ phosphors show four overlapping bands around 310, 325, 360 and 375 nm in addition to the characteristic of Eu²⁺ ions at 420 nm. These additional short wavelength bands were attributed to centres involving Tl⁺ ions. The decrease in PSL intensity of γ-irradiated KBr:Eu²⁺, Tl⁺ powder phosphors with Tl⁺ concentration and the absence of thallium emission bands in PSL were attributed to the efficient electron trapping by Tl⁺ ions during irradiation.     

Luminescence studies on swift heavy ion irradiated nanocrystalline aluminum oxide

Pellets of nanocrystalline aluminum oxide synthesized by a combustion technique are irradiated with 120 MeV Au⁹⁺ ions for fluence in the range 5×10¹¹-1×10¹³ ions cm⁻². Two photoluminescence (PL) emissions, a prominent one with peak at ∼525 nm and a shoulder at ∼465 nm are observed in heat treated and Au⁹⁺ ion irradiated aluminum oxide. The 525 nm emission is attributed to F₂²⁺-centers. The PL intensity at 525 nm is found to increase with increase in ion fluence up to 1×10¹² ions cm⁻² and decreases beyond this fluence. Thermoluminescence (TL) of heat-treated and swift heavy ion (SHI) irradiated aluminum oxide gives a strong and broad TL glow with peak at ∼610 K along with a weak shoulder at 500 K. The TL intensity is found to increase with Au⁹⁺ ion fluence up to 1×10¹³ ions cm⁻² and decreases beyond this fluence.     

Effect of Ce co-doping on KY3F10:Pr crystals

A spectroscopic investigation on the effect of Ce³⁺ co-doping in fluoride KY₃F₁₀:Pr³⁺ crystals is presented. In particular spectroscopic measurements of three different samples of KY₃F₁₀ crystal doped with 0.3at% Pr³⁺ and co-doped with 0at%, 0.17at% and 0.3at% Ce³⁺ are discussed. Details on the growth of the crystals are also reported. Measurements were performed in the temperature range 10-300 K. Fluorescence and lifetime measurements have shown a cross relaxation between ³P₀-¹D₂ levels of Pr³⁺ and ²F_7/2-²F_5/2 of Ce³⁺. Data exhibit that this effect is strictly related to the Cerium concentration.     

Theoretical studies on the SH parameters and local distortion structure of KCl:Ag crystal

Complete diagonalization of the energy matrix and high order perturbation formulae of spin-Hamiltonian (SH) parameters possessing D_4h symmetry for the 4d⁹ ion based on the crystal- and ligand-field theory in tetragonal symmetry are expressed and applied to the study of local distortion structure of the KCl:Ag²⁺ crystal. The calculated results agree well with experimental findings. Both complete diagonalization of energy matrix and high order perturbation approach are appropriate for the investigations of SH parameters of 4d⁹ ions in tetragonal crystals. Tetragonal distortion due to the Jahn-Teller effect for the tetragonal Ag²⁺ center at the K⁺ site of KCl crystal is also acquired from the calculations.     

Natural electron oscillations in granular aluminum films deposited on rough surfaces of NaCl and KCl single crystals

Granular aluminum films deposited on rough surfaces of NaCl and KCl single crystals form a two-layer coating. In the lower layer, a low-frequency band of plasma resonance is excited due to the joint action of a light-wave field and a field induced by granules-dipoles. In a small amount of granules of the upper layer isolated from each other, a high-frequency band with a frequency ω₀ of natural electron oscillations in the granules is excited. Using the measured frequencies ω₀ and the known dielectric constants of NaCl and KCl, a plasma frequency of aluminum is calculated that agrees well with the known plasma frequency of solid samples. Kharkov State University, 4 Svoboda Sq., Kharkov, 310077, Ukraine. Translated from Zhurnal Prikladnoid Spektroskopii, Vol. 66, No. 6, pp. 853–856, November–December, 1999.     

Kcl：Pb^2＋和RbCl：Pb^2＋单晶中HD色心的喇曼研究

本文报道KCl:Pb~(2+)和RbCl:Pb~(2+)单晶在温度77K经大剂量X射线辐照后的喇曼测量结果。根据高精度的偏振喇曼数据和最近发展起来的所谓表现型分析方法,确认频移为284cm~(-1)和270cm~(-1)的信号分别为KCl:Pb~(2+)和RbCl:Pb(2+)单晶中H_D色心的C_(1h)(010):A′动力学模振动引起的非弹性散射。     

The optical and paramagnetic absorption spectra of MgO:Mn single crystals irradiated in a reactor

The optical and paramagnetic absorption spectra of MgO:Mn crystals of different origin, irradiated in a reactor, have been investigated. It is found that, in spite of only a small amount of Mn²⁺ impurity ions in the investigated crystals, their influence on the efficiency of formation and accumulation of F⁺-centers is dominant. The dependence of the number of F⁺-centers both on irradiation dose and on manganese concentration is studied.     

Spectroscopic and crystal field studies of (Ce,Gd)Sc3 (BO3)4:Cr crystals

Complex spectroscopic studies of (Ce,Gd)Sc₃(BO₃)₄:Cr³⁺ (CSB:Cr³⁺) crystals (crystal growth, absorption and luminescence spectroscopy, crystal field calculations, analysis of the radiative and non-radiative decays) are presented. The main results of the paper include calculations of crystal field parameters and energy level scheme for Cr³⁺ at distorted octahedral Sc³⁺ sites, evaluation of the Huang-Rhys factor, effective phonon frequency, zero-phonon line energy, and parameters of radiative and non-radiative decays. Comparison with experimental results and other literature data is discussed. A very unusual value of the frequency factor (related to the non-radiative processes) is explained as being due to heterodesmic nature of chemical bonds in the CSB crystal. Cr³⁺-doped CSB crystals (with Cr³⁺ concentration 5.1×10¹⁹ cm⁻³ or 1%) are suggested as promising candidates for potential applications as active media for solid state lasers.     

Spectroscopic studies of Nd and Er in KGd(WO4)2 single crystals

Single crystals of KGd(WO₄)₂ doped with Nd³⁺ and Er³⁺ ions were grown by the top seeded solution growth method. Detailed analysis of the room-temperature absorption spectra was performed using the conventional Judd-Ofelt theory and actual dependence of the refractive index on the wavelength. In addition to the intensity parameters Ω_2,Ω_4,Ω₆, the branching ratios and radiative lifetimes were estimated for all possible transitions in the studied spectral region. Those transitions which can be potentially used for laser applications have been identified for both ions.