A.N.Trukhin , K.Smits, G.Chikvaidze, T.I.Dyuzheva, L.M.Lityagina
Luminescence spectrum of synthetic mono-crystalline stishovite comprises as low blue band at 400 nm
(3.1 eV) and a fast UV band at 260 nm (4.7 eV), as well as some bands in near-infrared range of spectra.The NIR luminescence of stishovite crystal, excited with lasers 532 nm, 248 nm and 193 nm as well as x-ray, possesses several sharp lines. Azerophonon line is situated at 787 nm (1.57 eV) and grows with cooling. An anti-Stokes line is located at 771 nm (1.68 eV). This line disappears with cooling. In a powder sample of stishovite created by shockwaves generated by the impact of a 50m-diameter meteorite in Arizona 50,000 years ago, the PL broad blue band is situated at 425 nm (2.9eV), the UV band at 260 nm (4.7eV), and the sharp lines, seen only under 193 nm laser, at 689 nm (1.789 eV), 694 nm (1.785 eV) and 706 nm (1.754 eV).
We ascribe the fast UV luminescence to singlet–singlet transitions and the slow blue band to triplet–
singlet transitions of the same intrinsic defect of stishovite in both types of samples. The blue band in
stishovite crystal exhibits delayed luminescence of recombination nature, whereas the blue band of Arizona’s powder sample does not exhibit such effect. This difference is explained by different surroundings of luminescence center in those samples. NIR luminescence of mono-crystalline stishovite is ascribed to carbon impurity penetrated in the sample from graphite heater. NIR luminescence of powder from Arizona has not yet found an explanation.
Solid State Communications 189(2014)10–14
A.N. Trukhin, K. Smits , A. Sharakosky , G. Chikvaidze , T.I. Dyuzheva , L.M. Lityagina
It is obtained that, as grown, non-irradiated stishovite single crystals possess a luminescence center.
Three excimer pulsed lasers (KrF, 248 nm; ArF, 193 nm; F2, 157 nm) were used for photoluminescence
(PL) excitation. Two PL bands were observed. One, in UV range with the maximum at 4.770.1 eV with
FWHM equal to 0.9570.1 eV, mainly is seen under ArF laser. Another, in blue range with the maximum
at 370.2 eV with FWHM equal to 0.870.2 eV, is seen under all three lasers. The UV band main fast
component of decay is with time constant t¼1.270.1 ns for the range of temperatures 16–150 K.
The blue band decay possesses fast and slow components. The fast component of the blue band decay is
about 1.2 ns. The slow component of the blue band well corresponds to exponent with time constant
equal to 1771 ms within the temperature range 16–200 K. deviations from exponential decay were
observed as well and explained by influence of nearest interstitial OH groups on the luminescence
center. The UV band was not detected for F2 laser excitation. For the case of KrF laser only a structure
less tail up to 4.6 eV was detected. Both the UV and the blue bands were also found in recombination
process with two components having characteristic time about 1 and 60 ms. For blue band recombination
luminescence decay is lasting to ms range of time with power law decay t1.
For the case of X-ray excitation the luminescence intensity exhibits strong drop down above 100 K.
such an effect does not take place in the case of photoexcitation with lasers. The activation energies for
both cases are different as well. Average value of that is 0.0370.01 eV for the case of X-ray
luminescence and it is 0.1570.05 eV for the case of PL. So, the processes of thermal quenching are
different for these kinds of excitation and, probably, are related to interaction of the luminescence
center with OH groups.
Stishovite crystal irradiated with pulses of electron beam (270 kV, 200 A, 10 ns) demonstrates a
decrease of luminescence intensity excited with X-ray. So, irradiation with electron beam shows on
destruction of luminescent defects.
The nature of luminescence excited in the transparency range of stishovite is ascribed to a defect
existing in the crystal after growth. Similarity of the stishovite luminescence with that of oxygen
deficient silica glass and induced by radiation luminescence of a-quartz crystal presumes similar nature
of centers in those materials.
Journal of Luminescence 131 (2011) 2273–2278