Electron paramagnetic resonance has been used to study the hole and electron paramagnetic centers formed in X-irradiated RbTiOPO4, the crystals of the KTP family. X-irradiation of RbTiOPO4 crystals at 77 K produced an oxygen hole center and four different trivalent titanium electron centers I" II, III and IV. The g-tensors, their principal values and axes for the defects were calculated and compared with those for KTiOPO4 centers. X-irradiation at 300 K produced another two oxygen hole centers and three electron centers I" 1 2 and II. EPR spectra of the center II revealed dissymmetrization, i.e., irregular distribution of growth defects, between the physically equivalent sites lowering the point group symmetry of the local environment of paramagnetic centers Ti'+

Electron paramagnetic resonance has been used to study the structure and thermostability of oxygen hole centers produced in KTiOPO 4 (KTP) crystals X-irradiated at 77 K. During the annealing of KTP crystals above 160 K the redistribution of charges took place. Four hole centers were observed at 40 K after the heating of the X-irradiated KTP crystal at different temperatures. The intensity of the hole center 1 decreased and new hole configurations (center 2 and center 3) appeared in the crystals. The g-matrices were obtained from the angular dependencies of EPR spectra. The p¡ g-values for center 1 were 2.0040, 2.0209, and 2.0437. The principal g-values for centers 2 and 3 were 2.0053, 2.0204, 2.0431 and 2.0035, 2.0183, 2.0628, respectively. The transformation of Ti 3+ speetra indieated that the trivalent titanium ions were involved into the recombination proeess. Subsequent annealing at temperatures above 220 K led to the formation of a new hole center 4 (ga = 2.0213, gb = 2.0236, gc = 2.0370).

In this work, the results of the hydrogen treatment and following that, the annealing in air of flux-grown KTiOPO 4 (KTP) crystals are represented. We have tried to correlate our optical and EPR results. The main conclusion is that the Ti 3+ A, B, C, D centers are not associated with optical absorption in the visible light region.

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