Characterising energy transfer upconversion in Nd-doped vanadates at elevated temperatures

The Energy Transfer Upconversion (ETU) macroparameter is measured for Nd-doped GdVO₄ and YVO₄ samples at temperatures ranging from Room Temperature (RT) to 450K, by means of a simple and automated z-scan technique. Furthermore, the ground state absorption cross section into the ²H_9/2 +⁴F_5/2 energy levels is characterised for both crystals over the same range of temperatures. The 808 nm π-polarisation absorption cross section is found to decrease from (58.6 ± 0.2) pm² to (30.9 ± 0.6) pm² for Nd:YVO₄ and (54.0 ± 0.3) pm² to (25.7 ± 0.5) pm² for Nd:GdVO₄, from RT to 450K. Over the same range the ETU coefficient decreases from (3.2 ± 0.7) 10^-16cm³/s to (1.8 ± 0.4 10^-16cm³/s and (5.0 ± 0.5) 10^-16cm³/s to (3.4±0.2) 10^-16cm³/s for 0.6 at. % and 1 at. % Nd:YVO₄ respectively, and (3.3 ± 0.5) 10^-16cm³/s to (0.8 ± 0.2) 10^-16cm³/s and (5.5 ± 0.5) 10^-16cm³/s to (3.1 ± 0.3) 10^-16cm³/s for 0.5 at.% and 1.1 at.% Nd:GdVO₄.