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

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.