Effect of ZrO2 and TiO2 on the micro-structure and NIR luminescence of mullite type Cr:Al4B2O9 glass ceramics

Boron-mullites are potential candidate crystal phases for broadband near-infrared (NIR) luminescence in the mullite series due to their higher complexity in crystal structure and abundant [AlO6] units for accommodating transition metal ions as luminescence activators. In this work, the effect of ZrO2 and TiO2 on the microstructure and NIR luminescent properties of mullite type Cr3+:Al4B2O9 glass ceramics were analyzed in detail. Through characterizations including XRD, SEM, TEM and NMR, the oriented growth of strip-shaped grains in ZrO2 doped glass ceramic samples has been verified. The proportion of [AlO6] units is strongly correlated with NIR spectra, suggesting that the strategy for modulation the NIR luminescence through oriented growth can be generalized as a universal method for manipulation of the optical properties for transition metal ion activated crystals with the mullite type structure.