Light Conversion upon Photoexcitation of NaBiF:Yb/Ho/Ce Nanocrystalline Particles.

NaBiF nanocrystalline particles were synthesized by means of a facile precipitation synthesis route to explore upconversion emission properties when doped with lanthanide ions. In particular, the incorporation of the Yb-Ho-Ce triad with controlled ion concentration facilitates near-IR pumping conversion into visible light, with the possibility of color emission tuning depending on Ce doping amount. We observed that introducing a Ce content up to 20 at.% in NaBiF:Yb/Ho, the chromaticity progressively turns from green for the Ce undoped system to red. This is due to cross-relaxation mechanisms between Ho and Ce ions that influence the relative efficiency of the overall upconversion pathways, as discussed on the basis of a theoretical rate equation model. Furthermore, experimental results suggest that the photoexcitation of intra-4f Ho transitions with light near the UV-visible edge can promote downconverted Yb near-IR emission through quantum cutting triggered by Ho-Yb energy transfer mechanisms. The present study evidences the potentiality of the developed NaBiF particles for applications that exploit lanthanide-based light frequency conversion and multicolor emission tuning.