Structural transformations and optical properties of glass-ceramics based on ZnO, β- and α-Zn2SiO4 nanocrystals and doped with Er2O3 and Yb2O3: Part I. The role of heat-treatment
Abstract
Differential scanning calorimetry, X-ray diffraction analysis, transmission electron microscopy, high- and low-frequency Raman and optical spectroscopy were applied to the study of structural transformations in glass of the K2O – ZnO – Al2O3 – SiO2 system codoped with Er2O3 and Yb2O3 and subjected to heat-treatments at 680–1300 °C. Transparent glass-ceramics based on ZnO nanocrystals are prepared by heat-treatments at 680–800 °C, while at 860–900 °C, β-Zn2SiO4 (β-willemite) nanocrystals precipitate in addition to ZnO; α-Zn2SiO4 nanocrystals appear additionally at 950 °C, and the material loses transparency. Opaque glass-ceramic prepared by heat-treatments at 1000 °C contains only crystals of ZnO and α-Zn2SiO4, while crystallization of potassium aluminosilicates, KAlSi2O6 (from the surface) and KAlSiO4 (from the bulk) in addition to ZnO and α-Zn2SiO4, is observed at above 1000 °C. Optical absorption and luminescence of the initial glass and GCs are reported. A shift of the UV absorption edge and the near-IR losses due to the free charge carrier scattering are indications of the ZnO crystallization. Multiple visible emissions from the glass and GCs are determined by the Er3+ ions, nanocrystals of α-Zn2SiO4 and defects of the ZnO nanocrystals. The color of the latter emission can be tuned by varying the heat-treatment temperature. The rare-earth ions (RE3+) do not enter into the Zn-containing nanocrystals and remain in the residual glassy phase until ~ 1200 °C, when the RE silicates (RE2Si2O7) are formed resulting in structured intense Er3+ emission.
- Publication:
-
Journal of Luminescence
- Pub Date:
- October 2018
- DOI:
- 10.1016/j.jlumin.2018.05.010
- Bibcode:
- 2018JLum..202...47L
- Keywords:
-
- Glass-ceramics;
- Zinc oxide;
- Willemite;
- X-ray diffraction;
- Raman spectroscopy;
- Low-frequency Raman spectroscopy;
- Luminescence