Highly efficient multi-colour upconversion emission of Yb3+/Er3+, Ho3+ codoped single LiYF4 octahedral microparticle

Abstract In this work, Yb 3+ /Er 3+ , Ho 3+ codoped tetragonal-phase LiYF 4 octahedral microparticles have been successfully synthesized through a facile hydrothermal method. Here, we implemented a confocal microscopy setup to manipulate and study the optical properties of a single LiYF 4 microparticle under a focused NIR 980 nm excitation. The strong multi-colour upconversion emission intensity with beautiful luminescent patterns have been clearly observed. And output colours (the different ratio of red-to-green emission intensity) of single LiYF 4 : Yb 3+ /Er 3+ , Ho 3+ microparticles have been anticipated to be adjusted by controlling Yb 3+ doping concentrations. The results show that the different ratio of red-to-green emission intensity of Er 3+ and Ho 3+ in single LiYF 4 microparticle, which is due to the cross-relaxation processes and energy back transfer processes between Yb 3+ ions and Er 3+ or Ho 3+ leading to different population densities of intermediate energy levels. The upconversion emission mechanisms and the influence of Yb 3+ concentrations on upconversion emission properties of Er 3+ and Ho 3+ ions are also discussed according to the emission spectra and rate equations.