Recombination luminescence in lead tungstate scintillating crystals

Room temperature radioluminescence and photoluminescence decay kinetics measurements of Ba-doped PbWO₄ crystals were compared with those of undoped and Mo-doped samples. Photoluminescence decay measurements focus on the coexistence of the immediate (fast) decay having a decay time of a few nanoseconds with slower delayed recombination decay processes. The radioluminescence emission peaking at 500 nm in Ba-doped crystals is similar to that observed in Mo-doped samples. However, photoluminescence of the Ba-doped crystals shows much faster decay kinetics with respect to that of PbWO₄:Mo. Wavelength-resolved thermally stimulated luminescence data (10–300 K) provides complementary information about trapping states and is correlated to photoluminescence decay kinetics.     

Electronic structure calculations of lead tungstate PbWO 4 crystals with defects of molybdenum impurity

Lead tungstate PbWO 4 crystals are one of the most effective scintillation materials for calorimetric devices designed to detect elementary particles with extremely high energies [1]. The interest to PbWO 4 scintillation and luminescence properties increased noticeably in the recent years [1, v 2]. However, experimental results obtained for PbWO 4 optical properties, substantially differ for crystals, produced under different growing conditions. Such a variety led to the situation, that up to now there are no generally accepted explanations for the origin of luminescence centres in PbWO 4 . The electronic structure of possible luminescent centres in perfect lead tungstate crystals PbWO 4 and in the crystals with molybdenum impurity PbWO 4 :Mo is ab-initio calculated in order to elucidate the origin of luminescence in lead tungstate crystals. Conclusions concerning excitation of self luminescence in perfect crystals and defect luminescence in Mo-doped crystals are made on the basis of results of calculations and experimental data on luminescence and photo excitation of PbWO 4 and PbWO 4 :Mo crystals.     

Raman spectra of undoped and uranium doped CaF2 single crystals

Raman scattering experiments for nominally pure and uranium doped CaF2 single crystals were presented.In all crystals, the Raman active T2g vibration mode of CaF2 was observed, whose frequency shift and fullwidth at half-maximum (FWHM) broadening correspond well with defects and impurities in CaF2 lattice.Additional Raman peaks develop in nominally pure CaF2 with high etch pits density and U6+:CaF2crystals. Part of additional Raman peaks in the experimental results, which are assumed due to vibration modes from F- interstitials and vacancies, are in well agreement with the theoretical predications by employing the Green-function formulation.     

Luminescence decay of lead tungstate and lead molybdate

The temperature dependence of the luminescence decay of PbWO₄ and PbMoO₄ has been investigated as part of an attempt to identify the nature of the unknown emitting centres. This dependence is found to be anomalous.     

Fascinating morphologies of lead tungstate nanostructures by chimie douce approach

Lead tungstate occurs in nature as tetragonal stolzite of scheelite (CaWO₄) type and monoclinic raspite. In this work, we report, the typical growth of snowflake-like tetragonal stolzite and bamboo-leaf-like monoclinic raspite nanocrystals of PbWO₄ via a simple aqueous precipitation method and a polyol (polyethylene glycol-200) mediated precipitation method at room temperature (27 °C). The synthesised PbWO₄ nanocrystals were characterised by XRD, SEM, EDAX and TGA–DTA. The UV-Vis absorption and photoluminescence studies of PbWO₄ nanocrystals in the two morphologies were performed. The nuclei of PbWO₄ nanocrystals in aqueous medium self-assemble in a tetragonal manner to form the snowflake-like crystals. In polyol medium, PbWO₄ nuclei preferentially grow by oriented attachment process to form the bamboo-leaf-like morphology. The specific morphology of the regularly assembled PbWO₄ nanocrystals in the two phases finds applications in nanoelectronics and photonics. Compared to other well-known scintillators, PbWO₄ is most attractive for high-energy physics applications, because of its high density, short decay time and high irradiation damage resistance.     

Collective excitation modes in the intermediate and superconducting states of doped and undoped indium and lead

Ultrasonic attenuation was studied in pure In, In + 0.003 at.% Pb, pure Pb and Pb + 0.003 at.% In in the intermediate states (for the magnetic fields 0.7H _c and 0.9H _c ) and superconducting states, for frequencies varying from 9.9 to 29.7 MHz, in the temperature range 4.2 to 1.4K. Collective excitation modes were observed in both the states for all the samples. There exist two distinct phases in the intermediate state but only one phase in the superconducting state in all the samples. The first phase was dependent on the magnetic field and independent of the concentration and nature of the dopant. The second phase was independent of the magnetic field and dependent essentially on the concentration of vacancies and marginally on the concentration of the dopant. The origin of the two phases has been discussed.     

Radioluminescence spectra of PWO crystals (co)doped by Ba

The influence of Ba (co)doping of PWO samples on the radioluminescence intensities has been tested. The codoping of the PWO:Mo,Nb crystals by Ba can increase markedly the intensities of the green luminescence, but only under the condition that the Ba concentrations fall into a limited concentration region. The green luminescence was also found in the PWO crystals doped only by Ba, and in the PWO crystals grown from melts with surplus of tungsten oxide. In the case of PWO:Mo,Ba crystals the increase of radioluminescence intensities with Ba concentrations is tentatively connected with inner stress caused by the difference in the size of Ba and Pb ions.     

Luminescence of photochromic centers in calcium fluoride crystals doped with Lu3+ ions

We report data on the luminescence spectra associated with photochromic centers in X-ray irradiated calcium fluoride crystals doped with Lu ions. Irradiation in low energy photochromic centers absorption band excites emission, which can be identify with transitions into photochromic centers. Ab initio calculation of absorption spectrum of photochromic center agrees rather well with experimental data.     

氟离子掺杂钨酸铅闪烁晶体的发光特性

钨酸铅(PWO)晶体是一种综合性能非常优异的无机闪烁晶体,并且在高能物理研究领域已获得重要应用,但光输出偏低的缺点严重制约了它在非高能物理领域的应用.本文采用氟化铅作为掺杂剂,用Bridgman方法生长出了光输出比普通PWO晶体高出2—3倍的新型PWO晶体.紫外和X射线荧光光谱的测试结果表明,这种新型晶体的发光波长比纯PWO晶体红移了大约134 nm,即为553 nm,衰减时间也从几十纳秒延长到100 ns以上,且光输出随积分时间的增加而增强.此外,发射波长和光输出沿晶体生长方向存在明显的位置依赖性,初期     

Defects generated by irradiation with gamma rays in lead doped KCl–KBr mixed single crystals

In this work we report the behavior of solid solutions of lead-doped KCl–KBr mixed single crystals subjected to gamma irradiation. Various composition of KCl_1−xBr_x (x=0.02, 0.35, 0.50, 0.65, 0.85) doped with 20–40 ppm of Pb²⁺ were used and exposed to ionizing radiation. The defect production seems to be correlated with the observed increasing integrated thermoluminescence glow curve as a function of irradiation at high 10 kGy dose as well as in the low 2.2–130 dose Gy range. The analysis shows the potential use of these mixed crystals as radiation detector. The defects generated by irradiation were monitored by the optical absorption spectrum and the thermally stimulated luminescence.     

Cathodoluminescence from deformed doped MgO crystals

The cathodoluminescence (CL) from indented Fe doped MgO single crystals has been studied with the scanning electron microscope and the results have been compared with the CL from undoped crystals. As in the undoped crystals, the iron doped crystals show in the deformed regions an enhanced luminescence emission but it has been found that iron acts as a quencher of luminescence. The results indicate that in the blue emission of the deformed crystals there is not a noticeable contribution of iron. From the evolution of CL with the irradiation time in the electron microscope it is concluded that the total Fe content influences the CL emission more than the Fe³⁺ content.     

Luminescent spectroscopy and structure of centers of the impurity Eu ions in lead tungstate crystals

Spectral-luminescent properties of the lead tungstate crystals doped with the Eu³⁺ ions were investigated in a wide temperature range at different excitation and registration wavelengths. The spectra consist of both weak wide nonstructural bands of the matrix emission and narrow spectral lines caused by inner f-f electron transitions in the impurity Eu³⁺ ions. The analysis and interpretation of spectral lines observed in excitation and luminescence spectra have shown formation of at least two different types of luminescent centers on the basis of the Eu³⁺ ions in the PbWO₄ crystals. These two types of centers are considered to be caused by arrangement of the impurity Eu³⁺ ions in Pb sites as well as in W sites of host matrix. For both types of centers values of S² scalar crystal field strength, and crystal field parameters were estimated and local site symmetries were found.     

Luminescence studies of rare earth doped yttrium gadolinium mixed oxide phosphor

This paper reports the photoluminescence and thermoluminescence properties of gamma ray induced rare earth doped yttrium gadolinium mixed oxide phosphor. The europium (Eu³⁺) was used as rare earth dopant. The phosphor was prepared by chemical co-precipitation method according to the formula (Y_2−x−yGd_x) O₃: Eu_y³⁺ (x=0.5; y=0.05). The photoluminescence emission spectrum of the prepared phosphor shows intense peaks in the red region at 615 nm for ⁵D₀→⁷F₂ transitions and the photoluminescence excitation spectra show a broad band located around 220–270 nm for the emission wavelength fixed at 615 nm. The thermoluminescence studies were carried out after irradiating the phosphor by gamma rays in the dose range from 100 Gy to 1 KGy. In the thermoluminescence glow curves, one single peak was observed at about 300 °C of which the intensity increases linearly in the studied dose range of gamma rays. The glow peak was deconvoluted by GlowFit program and the kinetic parameters associated with the deconvoluted peaks were calculated. The kinetic parameters were also calculated by various glow curve shape and heating rate methods.     

Optical absorption edge in doped and undoped ZnSe crystals

The optical absorption near the fundamental edge has been investigated for different types of doped and undoped cubic ZnSe crystals. Crystals grown from the vapour phase, with and without doping, and crystals grown by the chemical transport technique are compared.Results of absorption coefficient measurements made from 77 to 313 LK are discussed and it is shown that for undoped samples, the absorption tail is dominated by electrons-phonons interactions and Urbach's rule is nearly verified, whereas for doped samples the influence of defects is preponderant.     

Luminescence of KBr crystals doped with copper

Radiation produced in copper-doped KBr crystals with a maximum near 2.49 eV was investigated. Luminescence with a maximum at 2.49 eV is caused by excitation processes at luminescence centers, the structure of which includes interstitial positively charged univalent copper ions bound to divacancies and bromine ions. The copper-doped solid solution (K,Na)Br was used for observation of the transformation of luminescence centers and for increasing their concentration.S. M. Kirova State Pedagogical Institute, Pskov. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 79–82, September, 1993.     

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.     

Luminescence dating: laboratory procedures and protocols

In the last 30 years, from 1967 to 1997, the use of luminescence signals from naturally occurring minerals has gone though a major metamorphosis, from thermoluminescence (TL) dating of pottery to optically stimulated luminescence (OSL) dating of sediments. Laboratory procedures for dating sediments have been adapted from those for pottery and new procedures have been developed as the need arises.

The majority of sediment dating applications are carried out on quartz and potassium-rich feldspars and the general characteristics of the TL and OSL signals from these minerals are reviewed. For sediments some new problems were encountered, with some grains perhaps not being completely bleached at deposition. For OSL signals there is no simple procedure for the selection of a thermally stable signal, as there had been in the case of pottery.

Many different laboratory protocols have been developed as our understanding of the fundamental behaviour of luminescence signals from quartz and feldspar has improved. These protocols are explained and discussed, giving the advantages and disadvantages of each procedure as applied to different types of sediment.

This review is presented as a guide to the selection of the most appropriate procedure for a particular dating application.     

Luminescence properties of MgO produced by solution combustion synthesis and doped with lanthanides and Li

The objective of this study is to explore the possibility of synthesizing MgO with controlled luminescence and thermoluminescence (TL) properties using the Solution Combustion Synthesis (SCS) method by doping with different lanthanides (Ln) and co-doping with lithium (Li). The goal is to further establish the SCS technique as a new route for developing new TL and optically stimulated luminescence (OSL) dosimetric materials. Undoped and doped MgO samples were synthesized by SCS and characterized using radioluminescence (RL) and TL. The data obtained showed that Li doping can increase considerably the intensity of the RL and TL from Ln-doped MgO produced by SCS. In MgO:Ln,Li the introduced lanthanides are responsible for the emission during both RL and TL processes, although other emission bands are also observed (e.g., ∼700-750 nm). The incorporation of lanthanides also introduces trapping centers as indicated by different peaks in the TL curves. The results in this study show that the SCS technique can potentially produce materials with TL intensity comparable to commercial dosimetric materials, although further optimizations are still required.