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.