Optical Absorption and Photoluminescence Properties of Tb3+-doped KF-B2O3 Glasses

Abstract

The optical characterization of glasses, i.e., the study of optical properties such as glass transparency (in the UV, visible, and IR regions) and their capability to accept rare earth ions as the luminescent centers, is essential for their use in glass laser technology. During the last few years, a large variety of inorganic glasses have been developed and characterized [1±5]. Alkali uoro borate glasses can be considered to be laser hosts because of their optical transparency, both in the short wavelength region (necessary for getting the optimum ef®ciency of optical pumping of lasing ions) and high wavelength region (necessary for getting the maximum output intensity of laser radiation). Further, these glasses possess very low rates of crystallization, high transparency, and low toxicity. It is thus worthwhile to investigate the optical properties of an alkali uoro borate glass viz., KF-B2O3 doped with Tb 3‡. In this paper, we therefore report the results of our studies on several physical, optical, absorption, and photoluminescence properties of KF-B2O3 glasses doped with Tb 3‡ ions. We also attempted to apply the Judd-Ofelt theory to characterize the optical absorption and photoluminescence spectra of these glasses, and tried to evaluate various radiative properties such as transition probability, radiative lifetime of excited states, and emission cross-section of various emission levels. For the present study, a particular composition of 39KF-60B2O3 y 1TbF3 (all in mol %) was chosen. Details of the preparation of samples, optical absorption, and luminescence measurements were reported in our earlier papers [3±5]. From the measured values of density d, refractive index nd, and average molecular weight M, various other physical parameters such as Tb3‡ ion concentration Ni, molar refractivity RM, molecular polarizability ae, mean Tb3‡ separation distance ri, and the ®eld strength F (useful for the evaluation of radiative properties of these glasses) were calculated and presented in Table I. The optical absorption spectrum of Tb3‡ doped KF-B2O3 glasses recorded at room temperature in the visible region exhibited different absorption levels (Fig. 1); the prominent levels observed were assigned to the appropriate electronic transitions, as follows: F6 ! G6, L10, G5: