Use of smoke samples in diamond-anvil cells to measure pressure dependence of optical spectra: Application to the ZnO exciton

We present measurements of ZnO exciton peak energies, E₀, at pressures up to 107.3 kbar. Smoke samples consisting of randomly oriented single crystal particles were prepared by oxidizing metallic zinc in air and were collected on one diamond face of a Merrill-Bassett pressure cell. Pressures were measured by the ruby fluorescence technique. In the pressure range between 5 and 90 kbar, our results indicate a consistent linear dependence with dE₀/dP = 2.33 × 10^?3 eV kbar^?1 for both increasing and decreasing pressures. A mixed phase structure is suggested by the observed irregular peak shapes and measured pressure dependence for the sample that had been taken beyond ? 90 kbar where the transformation to the NaCl structure has been reported.