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1
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0022317057
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La Jolla, Calif. June 13–15, 1984, edited by P. Hammerling, A. B. Budgor, and A. Pinto (Springer, Berlin, Heidelberg, New York)
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(1985)
Tunable Solid State Lasers, Proceedings of the First International Conference
, pp. 129
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Feigelson, R.S.1
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5
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84950583178
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Although the ionic radius of [formula omitted] in fourfold coordination (0.44 Å) is much larger than the corresponding one for [formula omitted] (0.26 Å), substitution of Si(IV) in tetrahedral sites by Al(III), Ga(III), Fe(III), and Ge(lV) is well known in silicates. The ionic radii of the last three substituents is about the same as for [formula omitted] The relative stability of [formula omitted] in the tetrahedral site, as compared to [formula omitted] in the octahedral sites, could be due to the expected high covaleney of the Cr(IV) O(II) bond.
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6
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84950583175
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The Tanabe Sugano diagram for [formula omitted] ([formula omitted] configuration) in tetrahedral sites is similar to the one for [formula omitted] ([formula omitted] configuration) in octahedral sites. In the former case, the lowest energy transition [formula omitted] is symmetry forbidden, but because of vibronic effects it becomes weakly allowed. The characteristic of this kind of transition is that it is strongly affected by temperature. A considerable decrease of the strength of this transition was observed with cooling. At 16 K, many vibronic sidebands were observed in both the absorption and emission spectra. The zero phonon transition was observed in both spectra and lies at [formula omitted].
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7
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84950583176
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The ratio of absorption at 1100 nm to absorption at 740 nm, the latter one due to [formula omitted] in M2 sites 4, depends on the one fourth power of the oxygen partial pressure in the growth atmosphere, on the presence and concentration of a charge compensator, and on the [formula omitted] concentration. Postgrowth annealing in dilute hydrogen atmosphere causes loss of chromium but no change of the internal redox potential, thereby allowing the analysis of the dependance of the aforementioned ratio with [formula omitted] concentration. The experimental data agree well with the assumption of the presence of [formula omitted] in tetrahedral sites.
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