Orientedsilver chloride microcrystals and nanocrystals embedded in acrystalline KCl matrix, as studied by means of electron paramagneticresonance and optically detected magnetic resonance

Abstract

Self-trapped holes (STH), self-trapped excitons (STE) and shallowelectron centres in small AgCl crystals embedded in a KClcrystalline matrix have been observed by means of optically detectedmagnetic resonance (ODMR). The existence of the impurity clustersin heavily doped KCl:AgCl single crystals, ranging from single andpaired Ag ions to AgCl nanometre- and micrometre-size crystals(nanocrystals and microcrystals) retaining the orientation of thematrix, was confirmed. ODMR spectra were used as a fingerprint ofthe embedded AgCl microcrystals and a signature of theircrystallinity. For AgCl nanocrystals the anisotropy of theg-factor both for isolated STH and for STH forming STE was foundto be substantially reduced compared with those of bulk AgClcrystals and AgCl microcrystals embedded in KCl. This implies aconsiderable suppression of the Jahn-Teller effect innanoparticles. A rather general mechanism of the suppression of theJahn-Teller effect in nanocrystals is developed, taking intoaccount the additional deformation field appearing because of thestrong vibronic interaction at the interface. It allows evaluationof the critical size of the embedded AgCl nanocrystals, at which thesuppression of the Jahn-Teller effect has its onset; the valueobtained is ≈10 nm, in agreement with experiment.