Optical absorption and luminescence of LiTaO3:Cr and LiTaO3:Cr,Nd crystals

In this work we investigate spectroscopic properties of Cr3+ and Cr3+ - Nd3+ interaction in LiTaO3 using optical absorption, luminescence and luminescence decay times at temperatures between 5 K and 300 K. Some preliminary data obtained with singly doped LiTaO3:Cr at low activator concentration are given in our previous work. Recorded spectra indicate that both the Cr3+ and Nd3+ are located in several non- equivalent sites which differ in the strength of the crystal field. Luminescence spectrum of Cr3+ consists of a broad band whose maximum and intensity depend on temperature. Below about 50 K an additional sharp band with four distinct components appears in the spectrum. The broad band attributed to the spin allowed 4T2 - 4A2 transition of Cr3+ ions overlaps two absorption bands of Nd3+ ions at about 810 nm and 890 nm making the Cr3+ - Nd3+ energy transfer process feasible. Results of measurements are discussed and compared to those obtained with LiNbO3:Cr.