Proceedings Article | 23 March 2016
Proc. SPIE. 9765, Optical and Electronic Cooling of Solids
KEYWORDS: Refractive index, Glasses, Spectroscopy, Luminescence, Crystals, Ceramics, Ions, Quantum efficiency, Laser applications, Heat treatments, Solids, Ytterbium, Phonons, Laser crystals, Nanocrystals, Vitreous, Absorption
Laser cooling with anti-Stokes fluorescencewas predicted by Pringsheim in 1929, but for solids was only demonstrated in
1995. There are many difficulties which have hindered laser assisted cooling, principally the chemical purity of a sample
and the availability of suitable hosts. Recent progress has seen the cooled temperature plummet to 93K in Yb:YLF. One
of the challenges for laser cooling to become ubiquitous, is incorporating the rare-earthcooling ion in a more easily
engineered material, rather than a pure crystalline host. Rare-earth-doped nanocrystalline glass-ceramics were first
developed by Wang and Ohwaki for enhanced luminescence and mechanical properties compared to their parent glasses.
Our work has focused on creating a nanocrystalline environment for the cooling ion, in an easy to engineer glass. The
glasses with composition 30SiO2-15Al2O3-27CdF2-22PbF2-4YF3-2YbF3 (mol%), have been prepared by the conventional
melt-quenching technique. By a simple post fabrication thermal treatment, the rare-earth ions are embedded in the
crystalline phase within the glass matrix. Nanocrystals with various sizes and rare-earth concentrations have been
fabricated and their photoluminescence properties assessed in detail. These materials show close to unity
photoluminescence quantum yield (PLQY) when pumped above the band. However, they exhibit strong up-conversion
into the blue, characteristic of Tm trace impurity whose presence was confirmed. The purification of the starting materials
is underway to reduce the background loss to demonstrate laser cooling. Progress in the development of these nano-glass-ceramics
and their experimental characterization will be discussed.
