JUDD-OFELT ANALYSIS OF Tb3+ AND UPCONVERSION STUDY IN Yb3+–Tb3+ CO-DOPED CALIBO GLASSES

Abstract

We report on the study of the spectroscopic properties in Ytterbium-Terbium (Yb 3+-Tb 3+) co-doped calcium lithium borate (CaLiBO) glasses, with the study's focus being on the upconversion process. Intensity parameters Ω λ for CaLiBO:Tb 3+ are determined by the Judd-Ofelt method to be Ω 2 = 15.5 × 10-20 cm 2 , Ω 4 = 1.90 × 10-20 cm 2 and Ω 6 = 3.69 × 10-20 cm 2. We have also obtained electric-dipole (and magnetic-dipole) radiative transition probabilities, branching ratios, and lifetime for the Tb 3+ : 5 D 4 and 5 D 3 levels. In addition, an evaluation of the upconversion processes by luminescence and time-resolved spectroscopy were carried out. The upconversion rise and decay times, energy transfer probability from Yb 3+ to Tb 3+ ions, and the efficiency of the processes that depopulate the Tb 3+ : 5 D 4 level after resonantly pumping the Yb 3+ : 2 F 5/2 level were estimated. Our results showed that a cooperative energy transfer (CET) from two Yb 3+ ions to one Tb 3+ ion is the origin of the Tb 3+ upconversion luminescence in the visible region. While, CET followed of the cross relaxation or/and excited state absorption is responsible for the upconversion luminescence in the ultraviolet region.