Theory of photoluminescence decay and electric-field-dependent energy relaxation in disordered materials at low temperature

The authors present a systematic and exact evaluation of diffusivity, energy, photoluminescence (PL) decay and photoconduction for systems with energetic and positional disorder in the low-temperature limit. Whereas most quantities can be calculated analytically in the long-time limit (slowing down of relaxation), the PL requires explicit calculation of the total transition probability G_ij(t). The problem can be solved by a step-by-step approximation for a simplified PL model, emphasising the diffusional aspect. Finite electric fields lead to drastic modifications of relaxation laws at low temperature. They derive a formalism which can be applied with great generality in particular to amorphous semiconductors, quantum-well superlattices and disordered organic materials.