Nonradiative transition mechanism on the surface of nanocrystalllne La_(0.8)Sr_(0.2)FeO_3 probed by photoacoustic and surface photovoltaic techniques

摘要

Both photoacoustic spectroscopy and surface photovoltaic spectroscopy have been combined to probe the mechanism of nonradiative transitions on the surfaces and subsurfaces of crystalline La_(0.8)Sr_(0.2)FeO_3 nanopar-ticles at room temperature upon illumination of UV-near IR light. The deexcitation process of photogenic-free charge carriers was treated in detail. When the photon energy used was smaller than the photoelectric threshold of the nanoparticles, the deenergization processes of both exciton and crystal transitions field occurred mainly via the multiphonon nonradiative deexcitation. The electron-phonon interaction responsible for strong photoacoustic signals in the region dramatically increased with the decrease of the particle sizes, demonstrating a strong dependence on the density of surface localized states associated mainly with the Fe~(3+) cations, but not associated with the Si~(2+) and La~(3+) cations on the surface lattice of the samples.