Stokes and anti-Stokes photoluminescence of Rhodamine B in porous silicon

Rhodamine B (RhB) solution has been used to impregnate oxidised porous silicon (PS) in order to form RhB/PS nanocomposites. The photoluminescence (PL) mechanism of RhB/PS nanocomposites has been investigated through the effect of RhB concentration in solution and energy excitation. It was found that the energy transfer from PS nanocrystallites to RhB molecules is possible but it is not the principal route for radiative recombination. We note that chemical species on PS surface can play a key role on PL emission. An anti-Stokes photoluminescence (APL) has been observed when the excitation energy is in the range of PS photoluminescence band. The sublinear variation of the APL intensity with the laser power (IAPL∝P0.59) excludes the processes of two-step two-photon absorption as origin of this PL. We show that its origin is related to a second-order phenomenon where phonon absorption plays an important role.