Controlled phase-separation effect for enhanced optical refrigeration in yttrium-aluminosilicate glasses.

Silica glass is one of the most commonly used photonic materials. Fabrication through vapor deposition allows the large production of high-quality bulk and optical fibers, widely employed in light guidance and amplification. Recent research on optical refrigeration of ytterbium-doped silicate has drawn attention to its potential, demonstrating near-unity quantum yields with optical refrigeration measurements in both preforms and fibers. However, the low solubility of lanthanide and the high-phonon environment of a SiO₂ network poses limitations on material performance. In our study, Yb-doped yttrium-aluminosilicate (YAS) glasses were fabricated by a modified chemical vapor deposition process. The high concentration of rare-earth elements (Y + Yb) led to a phase separation effect visible only at the nanometer scale. Spherical amorphous domains showed elevated amounts of yttrium, aluminum, and ytterbium in contrast with the surrounding matrix. This unique feature significantly reduced the concentration quenching effects, even at a Yb density higher than 1026 ions per cubic meter, while promoting a low-phonon environment. Yb-doped yttrium-aluminosilicate samples with varying Yb density presented near-unity external quantum efficiencies, enabling optical refrigeration up to −2.4 K starting from room temperature under atmospheric pressure. [ABSTRACT FROM AUTHOR]