Low-temperature photoluminescence study of GeV centres in HPHT diamond

The temperature (in the range of 20–180 K) and pressure (up to 6.9 GPa) effects on the photoluminescence of GeV centre ensembles in high-quality HPHT microcrystalline diamond are studied. The pressure coefficient obtained for a GeV centre dE/dp = 3.29(2) meV/GPa allows us to separate the total observed temperature shift of the zero-phonon line (ZPL) into two parts: the contribution of the lattice thermal expansion and the contribution of the electron–phonon coupling. The contribution of the electron–phonon coupling to the ZPL temperature shift is found to follow a cT2 – dT4 polynomial law rather than a T3 power law dependence reported for the total observed temperature shift of the ZPL. At the same time, the temperature dependence of the width of the ZPL is found to be in good agreement with a T3 power law. Thus, the found temperature dependences indicate the predominant role of the strong softening of elastic springs in the excited state in the temperature effect on the photoluminescence of GeV centres. The temperature effect on the quasi-local vibrational mode is investigated for the first time. The energy of the quasi-local vibrational mode is found to decrease with increasing temperature, which can be associated with the anharmonicity effect. •The study of the pressure effect on zero-phonon line (ZPL) of GeV centre was conducted.•The study of the temperature effect on ZPL of GeV in temperature range of 20–180 K was conducted.•The contributions of lattice thermal expansion and electron-phonon interactions in a temperature shift of ZPL were separated.