Comparison of optical spectra of Nd³⁺in NdAl₃(BO₃)₄(NAB), Nd:GdAl₃(BO₃)₄(NGAB) and Nd:Gd_0.2Y_0.8Al₃(BO₃)₄(NGYAB) crystals

Abstract

A comparative study of the optical absorption and luminescence of crystals of NdAl3(BO3)4 (NAB), Nd:GdAl3(BO3)4 (NGAB) and Nd:Gd0.2Y0.8Al3(BO3)4 (NGYAB) is presented. The Judd-Ofelt theory is applied to the fitting of experimental absorption line strengths to obtain the intensity parameters Ωt (t = 2,4,6) with root mean square errors of 11.8%, 3.8% and 8.6% for NAB, NGAB and NGYAB respectively. The intensity parameters are used to calculate the radiative transition rates, branching ratios and radiative lifetimes of Nd3+ ions undergoing transitions from 4F3/2 to 4IJ manifolds. The relevant spectroscopic parameters for laser applications (quantum efficiency and emission cross section) are also estimated. The results are compared among the three samples and other borate crystals. It is concluded that NAB is a laser crystal with high gain and thus a promising candidate for microchip laser application, while NGAB (or NGYAB) can be used as an alternative to the celebrated nonlinear laser crystal NYAB.