The luminescence parameters of Yb3+:Er3+-doped LiLa(WO4)2 single crystal grown in the form of fiber for up-conversion green emission

Abstract This report details the first study of the luminescence properties of a single crystal grown in the form of fiber for prospective application as the gain medium for fiber laser emission at 552 nm. The excited state decay processes related with the 4 S 3/2 → 4 I 15/2 transition in double Yb 3+ :Er 3+ -doped LiLa(WO 4 ) 2 crystal have been investigated using time-resolved fluorescence spectroscopy with a Er 3+ concentration of 0.5 mol% and Yb 3+ with 2, 5, 7, 10 and 15 mol%. Selective laser excitation of the 2 F 5/2 energy level of Yb 3+ (972 nm) and selective laser excitations of the 4 I 11/2 and 4 I 13/2 energy levels of Er 3+ (972 and 1550 nm), respectively has established that in a similar way to other optical materials, a strong energy-transfer up-conversion by way of a dipole-dipole interactions between an Yb 3+ excited and Er 3+ ions, the 4 F 5/2 level (Yb 3+ ) populates the 4 S 3/2 upper laser level of the 550 nm transition. The 4 S 3/2 energy level emits luminescence with peaks having the wavelength center at 550 nm with luminescence efficiency increasing from 7% for Er 3+ singly doped to 36% for Yb 3+ (15 mol%) co-doped crystals. The 4 S 3/2 lifetime of Er 3+ is observed to increase due to the saturation of the multiphonon relaxation rate at high excited-state density of Yb 3+ ions. At high excited-state density, Yb 3+ ions saturates the accepting modes inside of a critical volume of R C =39.4 A centered at an excited Er 3+ ( 4 S 3/2 ) ion, by the high-energy phonons generated from emission sideband of Yb 3+ ions in Yb(x%):Er(0.5%) crystals. It is established that the green (552 nm) up-conversion luminescence of Er 3+ is optimized using an Yb 3+ concentration of 11.5 mol% for Er(0.5%):LiLa(WO 4 ) 2 crystal.