Spectroscopic investigation of Nd 3+ and Yb 3+ in Ca 4GdO(BO 3) 3 crystals

Gadolinium calcium oxoborate Ca₄GdO(BO₃)₃ (GdCOB) is a new efficient non-linear optical crystal belonging to the rare-earth calcium borate group with general composition Ca₄RB₃O₁₀ (R=La-Lu, Y). It exhibits efficient second harmonic generation (SHG) properties, a large transparency region and a high damage threshold. The compound Ca₄GdO(BO₃)₃ crystallises with a monoclinic acentric structure. The space group is Cm. Partial substitution of Gd³⁺ ions by other lanthanide ions leads to interesting studies of new laser materials.

In this paper we consider optical properties of Nd³⁺ and Yb³⁺ ions in Ca₄GdO(BO₃)₃. In this crystal neodymium ions act as donors of excitation energy, whereas ytterbium ions play the role of acceptors. We are interested in ion-matrix and ion-ion interactions such as electron-phonon coupling, and Nd-Yb excitation energy transfer. The infrared transmission and Raman scattering spectra were measured and the vibrational assignment is proposed. Absorption, emission and lifetime measurements have been carried out within the 5-300 K temperature range.