Growth and downconversion luminescence of Ho super(3+)/Yb super(3+) codoped alpha -NaYF sub(4) single crystals by the Bridgman method using a KF flux

Downconversion (DC) luminescence with emission at about 1000 nm under excitation of 448-nm light in Ho super(3+)/Yb super(3+) codoped alpha -NaYF sub(4) single crystal is realized. The crystal was grown by the Bridgman method using KF as an assisting flux in a NaF-YF sub(3) system. The energy-transfer process and quantum cutting (QC) mechanisms are presented through the analysis of the spectra. The energy-transfer processes of first- and second-order cooperative DC are responsible for the increase of the emission intensity at 1000 nm, and it is the first-order cooperative DC that is dominant for the DC process. When the Ho super(3+) concentration is fixed at about 0.8 mol%, the optimal concentration for 1000 nm emission is 3.02 mol% Yb super(3+) in the current research. The energy-transfer efficiency and the total quantum efficiency are analyzed through the luminescence decay curves. The maximum quantum cutting efficiency approaches to 184.4% in alpha -NaYF sub(4) single crystals of 0.799 mol% Ho super(3+) and 15.15 mol% Yb super(3+). However, the emission intensity at 1000 nm decreases while the energy-transfer efficiency from Ho super(3+) to Yb super(3+) increases, which may result from the fluorescence quenching between Ho super(3+) and Yb super(3+) ions, Yb super(3+) and Yb super(3+) ions. The present study involved Ho super(3+)/Yb super(3+) codoped alpha -NaYF sub(4) single-crystal growth, structure analysis, luminescence properties, luminescence decay curves and calculating data of the energy-transfer efficiency and the quantum cutting efficiency. The energy-transfer processes of first- and second-order cooperative DC are responsible for the increase of emission intensity at 1000 nm, and it is the first-order cooperative DC that is dominant for the DC process.