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 552nm. The excited state decay processes related with the 4S3/2→4I15/2 transition in double Yb3+:Er3+-doped LiLa(WO4)2 crystal have been investigated using time-resolved fluorescence spectroscopy with a Er3+ concentration of 0.5mol% and Yb3+ with 2, 5, 7, 10 and 15mol%. Selective laser excitation of the 2F5/2 energy level of Yb3+(972nm) and selective laser excitations of the 4I11/2 and 4I13/2 energy levels of Er3+(972 and 1550nm), 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 Yb3+ excited and Er3+ ions, the 4F5/2 level (Yb3+) populates the 4S3/2 upper laser level of the 550nm transition. The 4S3/2 energy level emits luminescence with peaks having the wavelength center at 550nm with luminescence efficiency increasing from 7% for Er3+ singly doped to 36% for Yb3+(15mol%) co-doped crystals. The 4S3/2 lifetime of Er3+ is observed to increase due to the saturation of the multiphonon relaxation rate at high excited-state density of Yb3+ ions. At high excited-state density, Yb3+ ions saturates the accepting modes inside of a critical volume of RC=39.4Å centered at an excited Er3+(4S3/2) ion, by the high-energy phonons generated from emission sideband of Yb3+ ions in Yb(x%):Er(0.5%) crystals. It is established that the green (552nm) up-conversion luminescence of Er3+ is optimized using an Yb3+ concentration of 11.5mol% for Er(0.5%):LiLa(WO4)2 crystal.