Structure and upconversion luminescence of transparent glass-ceramics containing (Er,Yb)2(Ti,Zr)2O7 nanocrystals

• Crystallization of titanate–zirconate (Er,Yb)2(Ti,Zr)2O7 nanosized (5–17 nm) crystals
• Their transformation from defect-fluorite to pyrochlore structure
• Optical absorption and upconversion luminescence spectra, and luminescence decay
• Enhancement (10-times) of red emission with the heat-treatment at 900–1000 °C

Transparent spinel-based glass-ceramics are synthesized on the basis of the magnesium aluminosilicate glass with the addition of nucleating agents (a mixture of TiO2 and ZrO2) and dopants, Er2O3 and Yb2O3, by a secondary heat-treatment at 800–1050 °C. The precipitation of rare-earth titanate–zirconate (Er,Yb)2(Ti,Zr)2O7 nanosized (5–17 nm) crystals is observed, as well as their transformation from the defect-fluorite to the disordered pyrochlore structure. Optical absorption and upconversion luminescence spectra are studied for various Er/Yb ratios, as well as for single Er-doped glasses and glass-ceramics. A substantial enhancement (10-times) of the red emission (~ 650 nm) with the heat-treatment is observed and explained with the analysis of the results of lifetime measurements of the 2H11/2, the 4S3/2, the 4F9/2 and the 4I11/2 excited states of Er3 + ions. The mechanisms of upconversion in (Er,Yb)2(Ti,Zr)2O7 nanocrystals are discussed.