Z. Moroz

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.

Effects of gamma irradiation and annealing treatments on the performance of Cr;Tm;Ho:YAG lasers

Spectroscopic studies of Cr;Tm;Ho:YAG (CTH:YAG) crystal samples after succesive procedures of gamma irradiation and annealing, were carried out. The emission characteristics of the free-running laser, doped with these ions were measured. Mechanisms which cause changes of the laser properties are discussed. Previously observed favourable changes of the optical and laser emission properties induced by thermal annealing and gamma radiation, are also confirmed. In particular, a substantial lowering of the emission threshold of the laser (after annealing) as well as an increase of the pumping efficiency (after gamma exposure) was obtained. It is argued, that this last effect is due to the sensitization process of the active Ho 3 ions.

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.

Excitation emission spectra of laser materials for UV-VIS range

Excitation-mission spectra have been measured for Pr3+, Ce3+, Nd3+ and Eu3+ doped YAP, YAG, and SLGO crystals in room temperature. Results of additional absorption measurements and changes in a luminescence after gamma irradiation with dose up to 105 Gy and energy of 2.5 MeV are also presented.

Valency change of Cr, Fe, Cu, Er, Ce dopants inside oxide compounds under proton irradiation

Abstract Valency changes of Ce, Er, Cu and Cr active ions and non-controlled Fe ions in Y 3 Al 5 O 12 :Ce and Y 3 Al 5 O 12 :Ce,Mg, SrGdGa 3 O 7 :Cr, YAlO 3 :Er and LiNbO 3 :Cr single crystals under proton irradiation were observed. For all investigated crystals the dose dependence of additional absorption was determined. For small proton fluencies (10 13 –10 14 particles/cm 2 ), the recharging effects are mainly observed. For fluencies greater than 10 14 cm −2 , the ionization effects and Frenkel defects are observed, for fluencies >10 15 cm −2 the Frenkel defects dominate. Changes in luminescence of Ce doped Y 3 Al 5 O 12 crystals depend on initial Ce concentration and are greater for Ce concentration 0.1 at.%. Gamma spectra from nuclear reaction products were also measured. The accuracy of the intensity measurement of the 0.208 MeV gamma line from 167 Tm in YAlO 3 :Er crystal is 0.14%, including the statistical and systematic errors. From extrapolation of the above result to lower Er contents, one can expect that 0.1 at.% is a detectable Er concentration level in the crystal.

Gamma-induced effect of recharging: Ce4+--Ce3+ in Ce3+ and Nd3+ doped YAG crystals

Gamma-induced transition of Ce4+

Influence of proton irradiation on optical characteristics of LiNbO3:Cu wafers

ARLR Ce3+ was investigated for Ce,Nd:YAG samples cut off from the same crystal and differing one to another by a few tenth percent of Ce3+ ions concentration (starting concentration). Depending on the starting concentration changes of resulting concentration of Ce3+ ions were observed. The luminescence of Ce,Nd:YAG crystal at about 530 nm increased independently on Ce3+ starting concentration.

EFFECT OF ANNEALING AND IRRADIATION ON THE OPTICAL PROPERTIES OF OXIDE CRYSTALS

Optical homogeneity (birefringence and birefringence dispersion mapping, transmission and additional absorption) was investigated on the entire areas of LiNbO3 wafers doped with Cu ions and irradiated with protons of fluencies ranging between 1012 and 1016 cm-2. The birefringence dispersion studies have revealed a considerable influence of protons on LiNbO3:Cu optical inhomogeneity, whereas the same influence on undoped LiNb03 was much less significant. The spectroscopic studies have revealed different mechanisms of defect formation depending on doses of protons. Also the secondary electrons generated by proton irradiation are believed to decrease the optical homogeneity by decreasing crystals conductivity and generation of the color centers.