Effects of hydrostatic pressure on the low-temperature photoluminescence spectrum of heavily doped CdS.

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The photoluminescence spectrum of heavily doped CdS is studied under pressure at 300 and 6 K in a diamond anvil cell. The pressure-induced shift of the broad green luminescence peak at 300 K is found to depend on the impurity content of the sample. At 6 K, the ${I}_{2}$ (donor-bound), ${I}_{1}$ (acceptor-bound), ${G}_{5}$ (bound-to-bound) excitons and the 1LO and 2LO replicas of ${G}_{5}$ are observed in addition to a red luminescence due to the Cd interstitials. The pressure coefficients of the excitons and the LO replicas are slightly lower than that of the band edge. The red luminescence, on the other hand, shifts at a rate of 7.28\ifmmode\pm\else\textpm\fi{}0.45 meV/kbar which is about 75% larger. These experiments did not indicate any pressure ionization of the donor impurities. No luminescence could be observed beyond the transition into an indirect-band-gap, rocksalt phase.