The effect of Cr doping on optical and photoluminescence properties of LiNbO 3 crystals

Abstract

Optical and photoluminescence studies on Cr doped LiNbO 3 single crystals have been carried out. Three different Cr doped compositions, with 0.1, 0.25 and 0.5 mol% Cr 2O 3, of congruently melting LiNbO 3 single crystals were grown by the Czochralski technique. Optical transmission studies showed prominent absorption bands in the visible region of the spectrum at photon energies of 1.9 and 2.57 eV. A significant red-shift of 60 nm was observed in the UV absorption edges of doped crystals. This can be explained in terms of the overall decrease in the Li/Nb ratio in the doped crystals, caused by extrinsic defects generated by the Cr 3+ impurity. The absorption coefficient of the material increases significantly with Cr doping concentration. The band gap decreases with increasing Cr concentration. The excitation-independent broadband luminescence was observed in the spectral range of 700–1100 nm, with a peak around 900 nm in the photoluminescence (PL) studies. The broadband PL emission makes the material a potential candidate for diode pumped all solid-state tunable laser.