Pressure-induced shift of energy levels and structural phase transition in CdSe/ZnS quantum dots

Electronic band structure of CdSe/ZnS quantum dots under high pressures is studied using fluorescence spectroscopy. We observe a strong blue shift of about 40 meV/GPa for the emission line at 655 nm. At moderate pressures (below 3GPa) this shift is linear and it is dominated by increase of the fundamental band gap of CdSe under pressure [1,2]. In contrast to bulk CdSe where the fluorescence is quenched above 3GPa as a result of the phase transition into the rock-salt structure [3,4], the CdSe/ZnS quantum dots remain structurally stable up to 6.5GPa. This structural robustness together with the high fluorescence yield and the large pressure-induced line shift, exceeding that of bulk ruby crystals by a factor of 40, make CdSe quantum dots a promising candidate for precise pressure calibration at moderate pressures.
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