Morphology evolution, tunable multicolor and enhanced upconversion luminescence via Li+ doping in Yb3+/Tm3+/Ho3+ tri-doped NaYF4 microcrystals

Abstract

In this paper, a range of Yb3+/Tm3+/Ho3+ triple-doped NaYF4 microcrystals (MCs) were successfully prepared by hydrothermal method and characterized by X-ray diffraction, which proved to be a hexagonal phase structure with uniformity. The morphology of NaYF4:20% Yb3+, 1% Ho3+ MCs with different doping amounts of NaOH and citric acid were studied using scanning electron microscope, and the distribution of elements of this doping system was characterized by energy dispersive spectrometer. Upconversion luminescence (UCL) spectra of the MCs using a fluorescence spectrometer with 980 nm excitation were researched, and the results demonstrated that the tunable multi-color of the MCs can be achieved by varying the doping amount of different rare-earth ions. The UC mechanism of the MCs were systematically described. Li+doped the series MCs improved their UCL efficiency. By investigating the UCL the MCs of the Li+-doped system, the emission intensities of blue (450 nm, 475 nm), green (541 nm), and red (648 nm) light of the series MCs were increased by 2.75, 2.095, 2.65, and 2.87 times, which is of great significance for its application in light-emitting diodes and solar cells.