Dynamics of electron–hole liquid condensation in CVD diamond studied by femtosecond pump and probe spectroscopy

Anomalous Blue Shift of Exciton Luminescence in Diamond

“…Figure a shows a mapping diagram of the temperature-dependent photoluminescence (PL) spectrum of a diamond produced by the high-temperature and high-pressure (HPHT) method excited by a 193 nm deep-UV laser. − (See the Supporting Information for Materials and Methods and Figures S1–S3.) As the temperature changes from 10 to 290 K, the PL spectrum of HPHT diamond exhibits phonon-assisted luminescence characteristics of the FE and EHL, including the phonon replicas of the FE, that is, FE TA , FE TO , FE LO , FE TO+OΓ , and FE TO+2OΓ , and the phonon replicas of the EHL, that is, EHL TO and EHL TO+OΓ , which are similar to those reported in previous research. ,, It can also be seen from Figure a that the temperature dependences of these emission peaks of FE-and EHL-related phonon replicas are quite different as the temperature rises (see Figure for the specific change process): The emission intensity of the former one increases first and then decreases with a blue-shifted trend shown by the peak position (see Figure S4 for the peak position change of FE TO and FE TO+OΓ excitonic peaks as the temperature rises) (i.e., it moves to higher-energy zone), whereas for the latter one, the emission intensity gradually decreases with the peak position, displaying a red-shifted trend (i.e., it moves to lower-energy zone).…”

“…13−15 replicas of the FE, that is, FE TA , FE TO , FE LO , FE TO+OΓ , and FE TO+2OΓ , and the phonon replicas of the EHL, that is, EHL TO and EHL TO+OΓ , which are similar to those reported in previous research. 5,16,17 It can also be seen from Figure 1a that the temperature dependences of these emission peaks of FE-and EHL-related phonon replicas are quite different as the temperature rises (see Figure 2 for the specific change process):…”

Optical study of carrier diffusion and recombination in CVD diamond

“…The critical temperature for EHL condensation (published value T C ¼ 165 K) is density dependent and in our case it was around 50-60 K [15]. The strong Auger recombination in EHL (monoexponential 1.5 ns decay due to constant density within EHL droplets [13]) which heats up the carriers can contribute to the observed increase of diffusion rate. The second reason influencing the value of measured diffusion coefficient is the formation of thermal grating at low temperatures.…”

“…This behavior can be explained by two different effects. The first one is the condensation of electron-hole liquid (EHL) occurring during 100 ps after excitation which in turn leads to an increase in the IR free carrier absorption [13,14] and correspondingly in the amplitude of the grating modulation. The critical temperature for EHL condensation (published value T C ¼ 165 K) is density dependent and in our case it was around 50-60 K [15].…”

Ultrafast Laser Processing of Diamond Materials: A Review

“…Possible applications are spatial phase modulation, high-speed optical switching and saturable absorption [11,12]. The availability of advanced technologies for the production of pure single-crystal diamond [13,14] allows to study the formation of electron-hole liquid (EHL) [15,16] in the material which can help to reveal the mechanisms of phase transitions occuring in a strongly excited diamond. These technologies have also allowed the formation of atomically flat diamond (111) surfaces that can subsequently undergo graphitization [17].…”