Effect of sensitizing Cr3+ ion on optical parameters of Nd-doped yttrium calcium oxyborate crystals

Abstract

Pure, Nd doped, and Nd–Cr bidoped yttrium calcium oxyborate Yca4O(BO3)3 (YCOB), NdxY1−xCa4O(BO3)3 (NYCOB) with x = 0.86, and Cr:NdxY1−xCa4O(BO3)3 (Cr:NYCOB) with x = 0.45 and a small amount of Cr3+ ions crystallized with a fluorapatite-type structure in the monoclinic system. The unit cell constants were a = 0.8076(7), b = 1.6020(10), and c = 0.3527(2) nm with the angle β of 101.23° for the NYCOB and z = 2. The measured absorption spectra of NYCOB and Cr:NYCOB were compared to Judd–Ofelt (JO) theory. When applied, the JO theory of parity-forbidden electric-dipole transitions of rare earth ions on noncentrosymmetric sites demonstrates good agreement. The experiments showed that the Cr3+ ions were introduced into the crystalline lattice as a sensitizer to absorb the excitation energy and transfer it to the Nd3+ ions in the lattice structure.