Stimulated emission from trapped excitons in SnO2 nanowires

The pump fluence dependent photoluminescence (PL) spectra of SnO₂ nanowires were investigated, which were synthesized with a high-temperature chemical reduction method. The integrated intensity of the narrower peak at 3.2 eV experiences a strong superlinear dependence on the pump fluence, and the narrowest width of the sharp peak is only 19 meV. Moreover, under high excitation fluence, an ultrafast decay time (less than 20 ps) appears in the time-resolved PL spectra. The emission of these SnO₂ nanowires shows strong apparent stimulated emission behaviors although the SnO₂ is a dipole forbidden direct gap semiconductor. The stimulated emission should relate to the localized islands on the surface of nanowire, which was observed through the high resolution transmission electron microscopy (HRTEM) image. The giant-oscillator-strength effect of bound exciton generated from the localized islands was considered to induce the stimulated emission of SnO₂ nanowires.