The configuration coordinate model has been used to calculate the luminescence band of CaWO4 at various temperatures. The force constant kg of the harmonic vibration in the ground state has been computed from the vibrational Raman spectrum of WO4/2~; the result is kg = 5.8 × 105dyne/cm. The force constant ke for the excited state, deduced from the temperature dependence of the width at half the maximum intensity of the emission band, iske = 1.5 × 105 dyne/cm. In order to obtain satisfactory agreement between theory and experiment we have to assume the variation in interatomic distance on excitation to be 0.20 Å which is in accordance with the analogous quantity of OsO4 where a calculation from spectroscopical data yields an expansion of 0.15 Å.
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