Comparative studies of luminescence in congruent and stoichiometric VTE-treated linbo3:Cr

Abstract The luminescence spectra of Cr3+ impurity have been studied in the wide spectral (11500 to 13900 cm−1) and temperature (5 to 300K) ranges for initially congruent grown LiNbO3:Cr3+ (0·1% mol.) specimens. The samples were further stoichiometrised using the Vapour Transport Equilibrium (VTE) procedure. In contrast to the congruent samples, for which in the region of supposed 2E-4A2 transitions in Cr3+ ions 7 emission lines were detected, 12 emission lines were observed in stoichiometric VTE specimens. Moreover, in VTE 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 4T2- 4A2 emission band. These new lines can be tentatively attributed to transitions in exchange-coupled pairs of Cr3+ ions.