Optical properties of ytterbium doped oxyfluoride glass-ceramics - Concentration and temperature dependence studies for optical refrigeration applications

Oxyfluoride glass-ceramics (GCs) doped with lanthanides have recently attracted much attention as a novel optoelectronic material candidate for optical refrigeration. In this study, the optical properties of highly transparent (~90% in the near infrared region) ytterbium doped germanate and aluminosilicate oxyfluoride glass ceramics with different rare earth ion concentrations varying from 0.5 to 3.0 mol % synthesized by the conventional melt quenching technique have been investigated to determine and compare their potential for optical refrigeration applications. The photoluminescence (PL) emission spectra at different temperatures (25°C–200 °C) were measured using different excitation wavelengths varying from 920 nm to 1030 nm in order to understand the behaviour of Stokes and anti-Stokes emission in all the glass-ceramics. The influence of ytterbium content is studied and found to substantially affect the PL emission and quantum yield and thus affect the cooling/heating characteristics. The highest intensity of anti-Stokes emission from the GC samples was observed in the composition containing 1.5 mol % or 2.0 mol % of Yb3+. Experiments monitoring the sample temperature at varying excitation wavelength between 1020 and 1030 nm demonstrates that the 1.5 mol % or 2.0 mol % Yb3+ concentrations are the most suitable for laser cooling applications.