Abstract
Oxyfluoride glass-ceramics are considered to be one of the promising materials for anti-Stokes laser cooling. Our previous results showed that glass-ceramics are more appropriate than glassy materials for laser cooling applications. In the present work, we describe the role of optimization of the oxide: fluoride ratio in oxyfluoride glass ceramics with the composition (SiO2-Al2O3)(100-x)(YLiF4)x: (YbF3)1 (x = 35 and 40; in mol.%) in order to obtain high photoluminescence quantum yield (PLQY) and low background absorption focusing on optical refrigeration applications. Glass-ceramics with high transparency (~ 90 % in the infrared region) were synthesized by the conventional melt-quenching process followed by heat-treatment. Near-infrared (NIR) photoluminescence (PL) emission due to the 2F5/2 – 2F7/2 Yb3+ transition, centered at ~1010 nm was observed. An improvement in the quantum efficiency is observed for all the samples, which varies between 64 % and 99 %, depending on the oxide: fluoride ratio. A decrease in the background absorption of the samples was investigated by calorimetry. The enhanced radiative (radiative emission) quantum efficiency is achieved due to the YLiF4 crystals (low phonon energy ~450 cm-1) which minimize non-radiative relaxations. At a laser wavelength of 1020 nm, the glass-ceramics show anti-Stokes PL emission, essential to achieve laser cooling. The proposed composition is an ideal candidate for laser cooling considering the low phonon energy and low background absorption compared to the other oxyfluoride glasses previously investigated.
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