2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/133280In this work I 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, I conclude with some hints of what I 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.8 pages, 7 figures. This is an extended version of another manuscript I wrote with occasion of the Michael D. Sturge prize 2007 (http://www.dpc07.org/). The shorter version of this paper will appear in an especial issue of Journal LuminescenceOther Condensed MatterMaterials Sciencetext