Multiphoton induced photoreduction in BaFCl: Sm³⁺ nanocrystals under femtosecond laser field

Photoinduced valence state conversion in lanthanide-doped solid materials can find significant applications in areas like optical storage, opto-electronic devices and has been attracting great research efforts. Here, we experimentally demonstrate that trivalent samarium ions contained in the BaFCl nanocrystals can be efficiently reduced to divalent ones under 800 nm fs laser field. The dependences of the luminescence intensity of the photoinduced divalent ions on the femtosecond laser power, central wavelength and polarization are investigated in detail, respectively. Theoretical fits of the experimental observations indicate that a resonance-mediated (2 + 2) four-photon absorption is most probably involved in the multiphoton induced photoreduction process.