Laser cooling of Er3+-doped low-phonon materials: Current status and outlook

In this work, we summarize some of the recent work carried out by our group on the upconversion dynamics of Er3+-doped potassium lead halide crystals, which possess very small phonons and present very efficient blue and green upconversion. Furthermore, a non-conventional application of these RE-doped low-phonon materials in optical refrigeration of luminescent solids is also discussed, paying especial attention to new pathways for optical cooling that include infrared-to-visible upconversion. Finally, we conclude with some hints of what we think it is the next step into improving the luminescence efficiency of solids: the use of RE-doped nanoscale photonic heterostructures for controlling the density of photonic states.