High-efficiency broadband anti-Stokes emission from Yb³⁺-doped bulk crystals.

We investigate the broadband anti-Stokes emission (BASE) from Yb³⁺-doped crystals with a laser diode (LD) pumping at 940 nm. Our experiment reveals that Yb³⁺-doped crystals with random cracks are able to generate bright BASE at room temperature and atmospheric pressure. By examining the various characteristics of the crystals and the emitted light, we supply a theory for interpreting the underlying physics for this variety of BASE. In particular, we take into consideration the effects of energy migration, avalanche process, and charge-transfer luminescence. This represents the first time, to the best of our knowledge, that BASE was obtained from Yb³⁺-doped bulk crystals with a high optical-optical efficiency.