Structural and optical characterizations of Yb~(3+) doped GeO_2-PbF_2-PbO glass-ceramics for optical refrigeration

摘要

We report on the structural and optical properties of 50GeO_2-30PbF_2-(20-x)PbO-xYbF_3, with x = 0.5, 1.5, 2.0, 2.5 mol% glass-ceramics for optical refrigeration. XRD measurements reveal the formation of nanocrystals embedded in glass samples after heat treatment at 360°C / 20h. Spectroscopic measurements show that samples have near infrared photoluminescence emission due to the ~2F_(5/2) - ~2F_(7/2) Yb~(3+) transition, centered at ~1020 nm with excitation at 919.7 nm, or 1011.2 nm, and the highest PL emission efficiency occurs for samples with 2.0 mol% of Yb~(3+). The PL quantum yield varies between 95% and 75%, depending on the lanthanide concentration and excitation wavelength, for 1.5 and 2.5 mol% Yb~(3+)doped samples being the most efficient under 1011.2 nm excitation. The UV-Vis-NIR spectroscopy shows a transparency as high as 80% in the infrared region, and the absorption between 900-1050 nm increases with Yb~(3+) concentration, in good agreement with the theoretical doping levels. Preliminary measurements monitoring the sample temperature dependence using a fiber Bragg grating sensor, as a function of pump laser wavelength and Yb~(3+) concentration shows that the heating process approaches zero for an excitation wavelength of around 1030 nm, which is an indication that phonons are annihilated in these glass-ceramic materials, and shows promise for applications in optical refrigeration.