The formation mechanism, optical absorption and emission spectra of Cr
4+ ions-containing Li
2O-SiO
2 system transparent glass-ceramics were investigated. In this material, the main crystalline phase was Li
2O•2SiO
2, and the percent crystallinity and crystal size were 67-72 and 20-33 nm, respectively. The remarkable change in color and absorption spectra was observed upon crystallization. The characteristic emission of tetrahedrally coordinated Cr
4+ ions was identified in the near infrared region, 1000-1600 nm. It was found that tetrahedrally coordinated Cr
4+ ions exist in this transparent glass-ceramics from absorption and emission measurement. The Cr
4+ ions exist in residual high SiO
2 glassy phase, and their ligand field parameters are estimated to be: 10Dq=10,610 cm
-1,
B=690 cm
-1 and Dq/
B=1.54. This Dq/
B value is just below the crossing point of
3T
2 and
1E levels (Dq/
B=1.6). The Cr
4+ ions in Li
2O-SiO
2 system transparent glass-ceramics occupy the little stronger ligand field sites than those in aluminate glass reported previously (Dq/
B=1.2). It is considered that the Cr
4+ ions can be formed by the reduction of Cr
6+ ions (chromate ion [CrO
4]
2-) associated with decreasing the basicity of residual glassy phase during crystallization. In this process the behavior of Li
+ ions plays a significant role. The [CrO
4] formed is equivalent to [SiO
4] and substitutes [SiO
4] sites in the residual high SiO
2 glassy phase.
抄録全体を表示