Properties of Anti-Stokes Photoluminescence and Ideal Laser Cooling Performance in Yb-Doped Yttrium Aluminum Garnet Thin Film

Abstract

We prepared Yb-doped yttrium aluminum oxide thin film on c-sapphire and fused-quartz substrates by a RF-magnetron sputtering technique for laser cooling application. The sputtered film on c-sapphire shows the high transparency, which is preferable for laser cooling application. The sputtering target of Yb-doped yttrium aluminum perovskite [(Yb:Y)AP] results in the eutectic phase of Yb-doped yttrium aluminum garnet [(Yb:Y)AG)] and Yb-doped yttrium aluminum monoclinic [(Yb:Y)AM)]. A PL spectrum of (Yb:Y)AG+(Yb:Y)AM/c-sapphire shows several strong, sharp peaks originated from the intra-orbital f-f transitions of Yb ions due to the weak reabsorption in the sputtered film. The ideal cooling efficiency of 1.5% in (Yb:Y)AG+(Yb:Y)AM/c-sapphire is comparable to that of a (Yb:Y)AG ceramics. These results suggest that the high laser cooling power is achievable in the sputtered film with high Yb-doping concentration.