Exciton absorption,photoluminescence and band structure of N-Free and N-DOPED In1−xGaxP

Optical absorption data on In_1?xGa_xP are reported showing the first observation of the exciton absorption peak in a III-V ternary alloy. This allows the most accurate determination to date of both the composition dependence of the Γ band gap and the position of the Γ ? X crossover (x_c = 0.72, 77°K; x_c = 0.73, 300°K). Absorptio and photoluminescence spectra are compared for both direct and indirect In_1?xGa_xP. In addition, absorption, photoluminescence, and luminescence lifetimes of In_1?xGa_xP:N are examined. These data suggest that the A-line is perturbed by alloy disorder and forms a broad luminescence band for x ? 0.94. The observed Stokes shift for the N-trap in the alloy is characteristic of an impurity strongly coupled to the lattice. The temperature dependence of the N luminescence band is found to be well described by the conventional configuration-coordinate model for phonon-coupled impurity luminescence. Implications of these results for light emitting devices are mentioned.     

A study of energy transfer between electronically excited states using a picosecond laser pulse

By means of a novel picosecond polarization spectrometer we have determined that under conditions of normal pumping of organic systems a substantial annihilation of excited states occurs before the 6–8 ps duration of the pumping pulse. The effect is exposed by noting that prior to 6 ps the optical absorption of the S₁ transient produced by 353 nm pumping of 1,2-benzanthracene is caused to be depolarized at higher concentrations. In another case (xanthone) where no long range interactions can occur the depolarization of the spectra only occurred at low concentrations due to saturation effects.