Light Conversion upon Photoexcitation of NaBiF 4 :Yb 3+ /Ho 3+ /Ce 3+ Nanocrystalline Particles.

NaBiF 4 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 3+ -Ho 3+ -Ce 3+ triad with controlled ion concentration facilitates near-IR pumping conversion into visible light, with the possibility of color emission tuning depending on Ce 3+ doping amount. We observed that introducing a Ce 3+ content up to 20 at.% in NaBiF 4 :Yb 3+ /Ho 3+ , the chromaticity progressively turns from green for the Ce 3+ undoped system to red. This is due to cross-relaxation mechanisms between Ho 3+ and Ce 3+ 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 3+ transitions with light near the UV-visible edge can promote downconverted Yb 3+ near-IR emission through quantum cutting triggered by Ho 3+ -Yb 3+ energy transfer mechanisms. The present study evidences the potentiality of the developed NaBiF 4 particles for applications that exploit lanthanide-based light frequency conversion and multicolor emission tuning.