Theory of the effects of hydrostatic pressure on the radiative transitions of impurities in crystals

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Abstract
The effects of hydrostatic pressure on radiative electronic transitions of impurities in solids are analyzed in the adiabatic approximation. A procedure is established for including the effects of pressure on the adiabatic potential for each electronic state. From harmonic configuration coordinates the effects of pressure on peak energy and half-width are determined classically for broad-band, phonon-assisted, absorption and luminescent emission spectra. The conditions for linear dependence of the peaks on pressure are clarified. The impurity is then considered quantum mechanically, and the effects of pressure on vibronic transition energies and probabilities determined. The pressure at which the zero-phonon transition becomes most probable is predicted for some defects. Finally, the effect of anharmonicity on the pressure dependence of vibronic transition energies is evaluated. From this study it is concluded that impurities with vibronic structure can be understood in great detail from the application of the theory to experimental pressure-dependent spectra.