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1990) Resonant raman scattering induced by pressure tuning of bulk and colloidal microcrystallite cadmium sulfide, High Abstract We have used Resonant Raman scattering induced by pressure tuning to study the phase transition of bulk and 40-80 .% colloidal microcrystallite CdS. The experimental results show that the bulk CdS undergoes a well defined first order phase transition at 27 kbas and the intensity of the Raman scattering increases sharply when the level of the intermediate state (bound exciton 12) is close to the photon energy. After the phase transition no Raman scattering and photoluminescence can be observed. However, the phase transition in the colloidal CdS is quit.e different from the bulk CdS and the phase transition occurs over a large pressure region up to 50 kbar. We attribute this different pressure behavior in colloidal CdS to the ollcvt, of surface reconstruction and large surface distortion energy of the SIILIII particles. Kev Words -Cadmium Sulfide, Resonant Raman, Phase transition, Colloidal Microcrystallite. Introduction Brafman and Mitra (1971) and Briggs and Ramdas (1976) studied the pressure dependence of LO phonon spectra in CdS and found that up to the phase transition LO phonon Raman scattering can be observed, whereas beyond the phase transition all Raman spectra disappear. However, recently Venkateswaren et al. (1984) have observed that the intensity of LO phonon first order Raman scattering chan es very little

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