Laser-driven proliferation of sp2-sp3 changes during anti-Stokes white light emission of μ-diamonds

Abstract

The paper presents the investigations of laser-induced white light emission (LIWE) and structural changes in diamonds after continuous wavelength near infrared laser excitation. Micro-size diamonds were synthesized using high pressure high temperature method and then excited using continuous wavelengths near infrared (808, 975, 1064 nm) laser diodes in vacuum. The structure and morphology of the samples were investigated before and after laser excitation using XRD, Raman spectroscopy and SEM/FIB and TEM microscopy. Broadband, intense, anti-Stokes LIWE with very low threshold were observed. LIWE resulted in the graphitization of the diamond grain surface with different stages of graphitization depending on the excitation time. A model of an sp2-sp3 hybridization switch process assisting the multiphoton ionization and free to bound recombination of electron between two carbon atoms were proposed.