Luminescence of localized states in silicon dioxide glass. A short review

The target is the description of the properties of localized states in silica glass, which relate to aspects of short-to-intermediate-range order. It has been observed that laser light interaction with localized states of silica glass leads to the creation of luminescence centers. Created luminescence centers, excited with laser light, provide intra-center luminescence of oxygen deficient centers (ODC) comprising a blue band at 2.7 eV and a UV band at 4.4 eV. Structurally, these ODCs are understood to comprise twofold-coordinated silicons that are commonly part of some larger local structure, and their luminescence bands can be suppressed by reaction with chlorine or hydrogen. Beside these processes laser light can give rise to charge separation. Recombination of well separated electrons and holes leads to recombination luminescence, which is similar to intra-center process luminescence but with greatly suppressed UV emission relative to the blue band and longer duration decay times. Evidence has been given that center of recombination at ODC sites involves an electron trap at the defect, whereas the hole is created as self-trapped holes (STHs) centers. Recombination results in the localized state recovering its initial state. Studies of temperature dependences of recombination luminescence intensity and decay show that intensive changes in these parameters take place in the known range of temperatures of STH liberation. Decrease of measured intra-center luminescence duration with increasing temperature is accompanied by less rapid decrease of recombination luminescence intensity. In the temperature range ~ 300 to 450 K, the blue luminescence intensity actually grows with heating, with little change in the decay time constant. As a rule, luminescence decay curves are non-exponential well described with stretched exponential function, showing first order fractal-kinetics. It is argued that discovered localized states of silica glass are connected with structure other than tetrahedrons. In dense silicon dioxide crystal with rutile structure (stishovite) luminescence similar to ODC luminescence of silica glass has been found.