Efficient down-shifting and up-conversion emission dual-mode in RE3+-doped NaTbF4-based nano-glass ceramics

Abstract

Undoped and RE³⁺-doped (Eu³⁺, Yb³⁺) nano-glass ceramics (nGCs) comprising NaTbF₄ nanocrystals (NCs) were obtained by thermal treatment of precursor sol–gel glasses. The structural characterization was carried out by X-ray diffraction, transmission electron microscopy and electron dispersive X-ray spectroscopy, which confirm that spherical cubic phase NaTbF₄ NCs were precipitated and uniformly distributed in the silica matrix. Additionally, in order to study the local environment of the dopant RE³⁺ ions and their distribution in nGCs, Eu³⁺ ions were considered as a spectroscopic probe. These materials present intense green and red emissions from Tb³⁺ and Eu³⁺ ions, respectively, both by down-shifting from UV-blue excitation, as well as cooperative up-conversion from 980 nm NIR excitation processes. In order to quantify the efficiency of all these emissions, the corresponding quantum yields were measured. Very efficient energy migration from Yb³⁺ to Eu³⁺ through Tb³⁺ ions made it possible to obtain long lived UC red emissions from Eu³⁺ ions, which are very useful in time-gated luminescence techniques. Through time resolved spectra and luminescence decay measurements, the involved energy transfer mechanisms were proposed. All these results allow considering these nGCs as dual-wavelength mode UV/NIR to VIS converter materials, with potential utility in solar cells, w-LEDs and anti-counterfeiting applications.