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The one- and two-photon-excited PL spectra at different temperatures. The dotted lines represent the one-photon excitation case and the solid lines, the two-photon-excitation case. The peaks marked with filled circles show the evolution of the exciton-LO-phonon emission peak. The dot-dash line is the transmission of the GaN film showing that the two-photon-excited PL peak is at the transmission edge of the sample.
(a) The PL decay of the one-photon-excited exciton emission peak at various temperatures. The room temperature PL decay times for both the 267 and excitations are about the same. The excitation intensity is more than three orders of magnitude lower than that using excitation. This indicates that the fast PL decay is not a result of a nonlinear recombination process (such as Auger) due to the higher excitation intensity at . (b) The two-photon-excited exciton emission decay at various temperatures.
The two-photon-excited exciton and exciton-LO-phonon emission lifetime as a function of temperature. The hollow triangles denote the experimental exciton emission, while the solid squares represent the experimental exciton-LO-phonon emission. As expected, the PL lifetimes of exciton and exciton-LO-phonon emission are about the same. The black curve is the theoretically fitted curve. Figure inset (a) shows the emission decay at different temperatures and the solid line is the single-exponential fit to the data and (b) shows the PL lifetime as a function of the location of the PL spot inside the sample.
The exciton lifetime as a function of emission wavelengths at .
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