Point Defects and Chromium(IV) Formation Mechanism in Gallia‐ and Alumina‐Based Oxide Glasses

Abstract

Point defects were found in as-quenched GeO 2 , 65CaOؒ 35Al 2 O 3 , and 65SrOؒ35Ga 2 O 3 glasses on the basis of electron paramagnetic resonance (EPR) measurements. These defects were identified as Ge E centers in GeO 2 glass and O − 2 , O − 3 , and M-OHC (oxygen hole center) (where M = Al, Ga) in 65CaOؒ35Al 2 O 3 and 65SrOؒ35Ga 2 O 3 glasses. The formation of Ge E centers in as-quenched GeO 2 glass was due to the thermodynamic stability of GeO at the melting temperature. The latter oxygen-excess defects are supposed to be formed by excess oxygen ions derived from the modifiers in the aluminate and gallate glasses during the formation of these glasses. To investigate some of the properties of the oxygen-excess defects in the calcium aluminate and strontium gallate glasses, chromium ions were doped in these glasses as a probe and the relationship between the valency state of the chromium ion and the defects was determined. We conclude that the peroxy bonding (−O−O−) oxidizes the Cr 3+ species to Cr 4+ . Similar defects have been identified in host compounds that are used for Cr 4+ tunable lasers. These results reveal that the point defects are necessary to stabilize the Cr 4+ ions in glasses and crystals.

Formation and quantification of peroxide anions in nanocages of 12CaO·7Al2O3

“…The photoreaction of these defects creates aluminum-oxygen hole centers (Al-OHC) and O 3 2 , both of which are detectable by EPR. 18,19 Similar defects are also observed in gallate glasses (65SrO?35Ga 2 O 3 ) prepared by high-temperature melting at 1800 K. 20 As we observed in our previous work, 4 metallic Pt evaporated on C 12 A 7 ceramic pellets was oxidized to Pt(IV) when annealed in an O 2 atmosphere at high temperature. Although oxidized Pt is thermodynamically stable in the presence of Ca below approximately 1100 uC, 21 Pt oxidation has only been observed on C 12 A 7 , especially when quenched from higher temperatures, and not on other calcium aluminates such as 3CaO?Al 2 O 3 (C 3 A) and CaO?Al 2 O 3 (CA).…”

Thermal characterisation of gallium-bismuthate oxide glasses

“…Due to their high optical nonlinearity, high magneto-optic effect and extended IR transparency heavy metal gallate glasses are of technological importance for potential application in optical switching, optical isolators used to avoid selffocusing in high power laser systems, IR windows and sensors [1][2][3]. Gallium-bismuthate glasses appear to be promising host materials for waveguide devices in the microwaves telecommunication windows, broad band amplifier and high power laser applications [4][5][6].…”

Thermally stable and tunable broadband near-infrared emission from NIR-I to NIR-II in Bi-doped germanate glass for smart light sources

“…2c). 52,53 However, the position and lineshape of the EPR signal changed slightly due to increasing Al 2 O 3 content, implying that the Ge E 0 center was located in a changing local environment. The Al 3+ ion with different coordinations can either enter into the germanate glass network to replace part of the Ge 4+ , or into the glass network gap as a charge compensator, which can cause distortions of the oxygen tetrahedral neighboring the E 0 -type center, thus lowering the symmetry from axial.…”