The effect of Cr doping on optical and photoluminescence properties of LiNbO3 crystals

Optical and photoluminescence studies on Cr doped LiNbO3 single crystals have been carried out. Three different Cr doped compositions, with 0.1, 0.25 and 0.5 mol% Cr2O3, of congruently melting LiNbO3 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 Cr3+ 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.