The influence of phase evolution on optical properties in rare earth doped glass ceramics containing NaYF4 nanocrystals

The crystal phase evolution from cubic α-NaYF4 to hexagonal β-NaYF4 was achieved in transparent oxyfluoride glass ceramics by modifying glass composition and rare earth doping. It was found that the development of compressive stress during the crystallization process may be responsible for the formation of β-NaYF4 nanocrystals. The incorporation of Eu3+ ions into the precipitated NaYF4 nanocrystals was verified and the difference of the distribution of Eu3+ ions in the glass ceramics resulted in remarkable changes in the emission spectra, such as the relative emission intensity, Stark splitting and fluorescence decay lifetimes. Bright and efficient upconversion luminescence was observed in the Er3+/Yb3+ co-doped glass ceramics and the corresponding upconversion mechanisms were analyzed.