Abstract
This paper reports the optical properties of Tb3+/Yb3+ co-doped lithium borate (LB) glass prepared by melt quench method. The absorption spectrum of the Yb3+ doped LB glass contains intense NIR band centered at 976 nm due to F-2(7/2)-> F-2(5/2) transition. The emission spectra of the prepared glasses have been monitored on excitation with 266, 355 and 976 nm. The Yb3+ doped glass emits a broad NIR band centered at 976 nm whereas the Tb3+ doped glass gives off visible bands on excitations with 266 and 355 nm. When the Tb3+ and Yb3+ ions are co-doped together, the emission intensity in the visible region decreases whereas it increases in the NIR region significantly. The increase in the emission intensity in the NIR region is due to efficient cooperative energy transfer (CET) from Tb3+ to Yb3+ ions. The quantum cutting efficiency for Tb3+/Yb3+ co-doped glass has been calculated and compared for 266 and 355 nm excitations. The quantum cutting efficiency is larger for 355 nm excitation (137%). The Tb3+/Yb3+ co-doped LB glass also emits upconverted visible bands on excitation with 976 nm. The mechanisms involved in the energy transfer have been discussed using schematic energy level diagram. The Tb3+/Yb3+ co-doped LB glass may be used in the optical devices and in solar cell for solar spectral conversion and behaves as a multi-modal photo-luminescent material.