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(a) Room temperature stimulated emission of band from a ZnO pellet under nonresonant two-photon excitation using for various excitation intensities. (b) Time-integrated PL spectra at room temperature at as a function of the excitation wavelength.
(a) Time-integrated PL spectra at under one-photon excitation for various excitation intensities showing the evolution of the spectral features. (b) Time-integrated PL spectra obtained under the same conditions, but where now the sample is excited by nonresonant two-photon excitation at . The observed PL lines are identified as free excitons and biexcitons , band, BX, TES, phonon replicas of free excitons and TES, (1-LO, 2-LO, and 1-LO TES), and DAP.
-band PL intensities from Fig. 2(a) (green dots) and Fig. 2(b) (red dots) determined by the simultaneous fits to the band with the and BX lines. The superimposed solid curves are the steady-state solutions to the simultaneous rates equations under one-photon and two-photon excitation, respectively.
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