Fine structure of the photoluminescence spectrum of diamond under the multiple emission of an optical phonon during the autolocalization of photoexcited electrons

The autolocalization of electrons photoexcited by laser pulses with a wavelength of 525 nm in the visible range and with a duration of 150 fs in an electron-hole plasma (density $\sim$10$^{21}$ cm$^{-3}$) in natural diamond at room temperature occurs unsteadily through step-by-step multiple (up to nine acts) emission of an optical phonon at subpicosecond times. This process is manifested for the probe photoluminescence signal in its fine periodic structure in the band gap beginning from the interband absorption edge. The intensity of multiphonon photoluminescence peaks reaches a maximum after four to six emission acts, where the energy of an electron-softened optical phonon is recovered and the broadening of peaks increases monotonically. Attributing the broadening of peaks to the kinetics of the emission of a successive phonon, one can compare their widths to the time dynamic scale of the electron-hole plasma and multiphonon emission during autolocalization. Then, the initial increase in the intensity of the peaks demonstrates the emission of phonons during autolocalization, whereas saturation and subsequent decrease are due to the subpicosecond Auger recombination of the plasma, which significantly suppresses photoluminescence because of the sharp decrease in the hole density (to 10$^{19}$ cm$^{-3}$), but not the process of autolocalization itself.