The dependence of CW photoluminescence on excitation energy in a-P

The dependence of the photoluminescence of red amorphous phosphorus upon the energy of excitation photons is discussed in the framework of models of recombination at defects. The CW luminescence of this material at 4 K is found to show a shift in the emission energy proportional to the excitation energy below a critical energy near the bandgap. Near the same energy the width of the luminescence band switches from being linearly related to the excitation energy (low energies) to being independent of excitation energy (higher energies). The authors discuss the role of the processes involved in absorption in determining the excitation dependence of the luminescence, and conclude that the sharpness of the transition from linear variation with excitation energy to independence of energy indicates the influence of the mobility edge upon the initial distribution of optically injected carriers.