Ryszard Jablonski

Radiation Defects in Oxide Compounds

Yttrium-aluminum garnets, strontium and barium lanthanum gallates, lithium niobate and tantalate as-grown crystals and doped by diffusion with rare-earth (Nd, Dy, Er, Tm, Ho, Pr, Ce) and metal transition elements (Mn, Cr) were investigated optically and using Electron Spin Resonance method before and after gamma, electron and proton irradiation.

Electron spin resonance and optical measurements of yttrium ortho-vanadate, doped with Nd3+ ions

Abstract The electron spin resonance and optical properties of YVO 4 and YVO 4 :Nd 3+ crystals before and after ionizing radiation treatment with gamma quanta and electrons are presented. The obtained YVO 4 and YVO 4 :Nd 3+ (1 at. % Nd) single crystals show a lower content of point defects (growth defects, e.g. oxygen vacancies) and consequently, lower susceptibility to ionizing radiation in comparison to YAG: Nd 3+ crystals. Because of the angular dependence of the Nd 3+ resonance line position, we suppose the presence of structural defects like twins and mosaic structure. Moreover, for the first time the ESR spectrum of V 4+ in YVO 4 is reported.

ESR and optical measurements of LiNbO3 and LiTaO3 single crystals doped with ions of the first transition series

Abstract The results of ESR measurements on LiNbO3 single crystal doped with Fe3+, Cr3+, Mn2+ or Cu2+ and also LiTaO3 doped with Cu2+ ions are presented. The absorption spectra of these crystals before and after γ and electron irradiation are described. The IR absorption band of the OH− group is analysed to determine the most probable location of Cu2+ and Fe3+ ions in the LiNbO3 lattice.

Changes in optical properties of YAG:Ce single crystals due to codoping and ionizing radiation treatment

Absorption, luminescence, ESR and ESA spectra and TL glow curves of YAG:Ce crystals codoped with Mg2+ ions and subjected to various treatments have been measured. The variations induced by irradiations in gamma and proton beams, and by thermal annealings under oxidation and reduction conditions point to large variations of the cerium ion valency. The ESA spectra of Mg-free and Mg-codoped crystals are clearly different with the peak value in the YAG:Ce, Mg sample higher and shifted towards the shorter wavelengths. Although the TL glow curves reveal the existence of the same major traps in both materials, their role in the overall deexcitation process is strongly modified upon Mg-codoping.

Radiation defects in SrLaGa3O7 crystals doped with rare-earth elements

Abstract Influence of γ and proton exposures on the optical absorption and photoluminescence of SrLaGa3O7 (SLGO) single crystals doped with Nd, Dy and Pr was studied. We observed that color centers, which appeared after the irradiation, shift the short-wave absorption edge towards the longer wavelengths by a few hundreds nm. They are probably attributed to the Ga2+ centers which are formed according to the reaction Ga3+xa0+xa0e−xa0→xa0Ga2+ with a spin of S= 1 2 , g||=1.9838(5) and g⊥=2.0453(5).

Growth and characterization of lithium tantalate single crystals doped with Ho, Tm, Nd, Yb, Pr and doped by diffusion with Cr and Cu

Crystal growth conditions for lithium tantalate single crystals doped with rare-earth and conditions of the diffusion process for doping with Cr and Cu are described. Absorption and an additional absorption after g-irradiation and annealing treatments at room temperature 5 were measured. The g-irradiation with a dose of 10 Gy and subsequent annealing at 8008C in air for 3 h lead to a valency change of Ho and Pr ions. In the case of g-irradiation a recombination process due to the Compton effect seems to be responsible for the valency change process in both crystals. Luminescence and radioluminescence measurements in UV1VIS range were also performed which show a weak excitation energy transfer from the LiTaO lattice to impurity ions. ESR investigations were performed which suggest probable 3 1 51 localization of impurities incorporated by diffusion at Li sites, impurities incorporated during growth at Ta or interstitial sites and also strong structure deviations in Nd, Yb:LiTaO as compared to LiNbO single crystals. All single crystals under tests reveal good optical 33 quality and higher absorption than in the case of yttrium-aluminate garnets and lithium niobate with similar level of rare-earth concentration.

Radiation defects in LiNbO3 single crystals doped with Cr3+ ions

Absorption and additional absorption of LiNbO 3 crystals doped with Cr 3+ during growth or by diffusion process were investigated before and after γ-irradiation with a dose of 10 5 Gy and also before and after proton irradiation with a fluency of 10 14 cm -2 . It was found that chromium ions may be mtroduced into LiNbO 3 crystals also as Cr 2+ . ESR measurements of Cr:LiNbO 3 crystals irradiated by γ-rays and electrons were performed. Paramagnetic peak after γ and electron irradiation was observed, which vanishes after annealing at 400°C for 3h both in optical and ESR spectra. Mn 2+ lines were also observed, which diminish after electron irradiation only.

Recharging Processes of Chromium Ions in Cr:SrGdGa3O7 and Cr:SrLaGa3O7 Single Crystals

Growth and recharging processes of chromium ions in SrGdGa 3 O 7 and SrLaGa 3 O 7 single crystals incorporated during growth or doping by diffusion (only for SrLaGa 3 O 7 crystal) were analyzed. The annealing at 1000°C in air and ionizing with gamma rays (doses from 10 3 to 10 5 Gy) and protons (10 14 cm -2 only for SrGdGa 3 O 7 crystal) were performed. Different kinds of chromium ions valency, from two to four, were found. Electron spin resonance measurements in the temperature range 5-300K with the use of Brucker spectrometer were also done.

Growth and optical properties of Nd:YVO4 laser crystals

Growth conditions for Nd:YVO4 crystals and some optical properties are presented. The obtained Nd:YVO4 crystal shows lower content of point defects and consequently, lower susceptibility to ionizing radiation. ESR measurements show the presence of V ions in interstitial sites with another than 5t valency. Obtained by Czochralski method crystals reveal very good optical properties, some of which are better than for Nd:YAG.

Radiation defects in BaLaGa3O7 crystals

Abstract The effect of γ-exposure from a 60Co source on the electron spin resonance (ESR), absorption and thermoluminescence of BaLaGa3O7 (BLGO) single crystals undoped and doped with Nd− ions was investigated. A radiation defect connected with the shifting of a short-wave absorption edge is described. Obtained results can be explained by an assumption of the following process: Ga3+ ion captures the electron which was knocked out by γ-irradiation from O2− ion and in a consequence Ga2+ paramagnetic centre is formed.