Optical high excitation of diamond: phase diagram of excitons, electron–hole liquid and electron–hole plasma

Abstract

High pressure synthetic diamonds were optically excited across the band gap by laser pulses from combined Nd:YAG and dye laser systems after frequency doubling and tripling. The output pulses had wavelengths in the range of λ=220 nm ( hν≈5.6 eV) and pulse energies up to 550 μJ. Crystal temperatures were in the range from 80 K to room temperature. Under this strong optical pumping we observe in steady state measurements recombination radiation from the electron–hole liquid, a condensed intrinsic state of the charge carries with high densities of approximately 10 20 cm −3, emitting luminescence in various wave vector-conserving phonon replicas (TA, TO, TO+O Γ). Virtually noise-free measurements allow us to make precise line fits to the spectra and to deduce a density-vs.-temperature, n( T), phase diagram of the liquid and gaseous phases.