SPIE, Vol. 3178, 279-282, 0277-786X/97/$10.00 279 Gamma-induced effect of recharging: Ce 4+ ↔ Ce 3+ in Ce 3+ and Nd 3+ doped YAG crystals S. Kaczmarek 1 , M. Kwaśny 1 , J. Kisielewski 2 , Z. Moroz 3 , A.O. Matkovskii 4 , D.Yu. Sugak 4 1-Institute of Optoelectronics, Military University of Technology, 2 Kaliski Str., Warsaw, Poland, 2-Institute of Electronic Materials Technology, 133 Wólczyńska Str., 01-919 Warsaw, Poland, 3-Institute of Nuclear Problems, ĝwierk, Poland, 4-SRC Carat, Institute of Materials, 202 Stryiska Str., 290031 Lvov, Ukraine. ABSTRACT Gamma-induced transition of Ce 4+ ↔ Ce 3+ was investigated for Ce,Nd:YAG samples cut off from the same crystal and differring one to another by a few tenth percent of Ce 3+ ions concentration (starting concentration). Depending on the starting concentration changes of resulting concentration of Ce 3+ ions were observed. The luminescence of Ce,Nd:YAG crystal at about 530 nm increased independently on Ce 3+ starting concentration. Keywords: absorption, luminescence, gamma-radiation, colour centers. 1. INTRODUCTION Gamma irradiation can have positive influence on some properties of different materials 1, 2 . It is due to the ability of this radiation to create not only structural defects, but also to annihilate inherent defects. Especially rebuilding and overcharging mechanisms have been used to create center defects in ionic crystals in case of preparation of new materials for opto-electronic devices and laser elements 3 . It is well established 4 , that Ce 3+ ion (0.02 wt%) built in pure YAG crystal decreases, while introduction of the same content of Ce to Nd:YAG crystal increases susceptibility of the crystal to gamma radiation. In the latter case optical density in the UV range and visible part of the absorption coefficient spectrum increases appreciably. As it was stated 5 the intensity of the gamma-induced additional absorption (AA) for Ce,Nd:YAG crystal in complex manner depends on Ce ions concentration: namely it increases with concentration up to 0.1 wt% and appreciably decreases for further increasing of Ce concentration. Hence , introducing in special conditions Ce ions, it is possible to increase radiation stability of Nd:YAG crystal 6 . In present work we undertake an attempt to describe influence of gamma- radiation with doses up to 10 5 Gy on absorption and luminescence spectra of Ce,Nd:YAG crystal. 2. EXPERIMENTAL SETUP 2.1 Crystal growth The investigated crystals were pulled by the Czochralski technique from iridium crucibles in the Institute of Electronic Materials Technology. The growth was performed in the N 2 atmosphere with addition of about 2% (vol.) O 2 . The growth rate was 0.9 mm/h and the rotation rate 10-20 rpm. As the starting materials Y 2 O 3 , Al 2 O 3 , Nd 2 O 3 and CeO 2 of at least 4N purity were used. We assumed that Ce 4+ ion enter in garnet lattice as Ce 3+ , that is the following reaction takes place: 2CeO 2 → Ce 2 O 3 + 1 2 2 O (1) This statement is not fulfilled for each Ce 4+ ion however. The heated mixture has therefore the form: ( ) ( ) 3 2 5 2 23 23 2 23 3 5 12 - - + + + → -- x yYO xNdO yCeO AlO Y Nd Ce AlO xy x y (2) x and y are chosen according to the required Nd and Ce concentration values taking into account, that x×100/3% and y×100/3% are atomic percentages of Nd and Ce concentration, respectively. This description does not take into account Ce ion with another valency. As the effect Ce, Nd:YAG (0.05 at% of Ce 3+ and 1 at.% of Nd 3+ ) crystals of yellow colour were obtained. 2.2 Spectroscopic investigations