CuCl nanocrystals in alkali-halide matrices under hydrostatic pressure

CuCl nanocrystals in crystalline alkali-halide matrices have been investigated under hydrostatic pressures up to 18 GPa. The pressures of structural phase transitions in CuCl have been determined both for different nanocrystal sizes and for different matrices (NaCl, LiCl, KCl). For CuCl nanocrystals in NaCl an increase of the transition pressure with decreasing nanocrystal size is observed, which is explained by the increasing importance of surface pressure for small nanocrystals. We found higher transition pressures for the LiCl matrix than for the NaCl matrix. The reason for this is that the pressure which acts on the nanocrystal differs from the external pressure. A simple elastic model describes the effective pressure transmitted from the matrix to the nanocrystal. With CuCl nanocrystals embedded in KCl we have studied the behavior of nanocrystals during a phase transition of the matrix. Additionally we have determined the pressure coefficients of the exciton energies of the CuCl nanocrystals, which depend on the elastic properties of the matrix. Received 4 March 1999