Comparative studies of luminescence in congruent and stoichiometric VTE-treated LiNbO3 : Cr

The luminescence spectra of Cr3+ impurity have been studied in the wide spe ctral (11500 to 13900 cm(-1)) and temperature (5 to 300K) ranges for initia lly congruent grown LiNbO3:Cr3+ (0.1% mol.) specimens. The samples were fur ther stoichiometrised using the Vapour Transport Equilibrium (VTE) procedur e. In contrast to the congruent samples, for which in the region of suppose d E-2-(4)A(2) transitions in Cr3+ ions 7 emission lines were detected, 12 e mission lines were observed in stoichiometric VTE specimens. Moreover, in V TE crystals, we observed 5 so far unknown polarized lines centered at 12801 , 12530, 12215, 11980 and 11720 cm(-1) (T=80K) on the short-wavelength side of T-4(2)- (4)A(2) emission band. These new lines can be tentatively attri buted to transitions in exchange-coupled pairs of Cr3+ ions.