Self-Trapping of Excitons in PbI₂Clusters Formed in Pb_1-xCd_xI₂Mixed Crystals

Abstract

Luminescence of PbI 2 clusters formed in Pb 1- x Cd x I 2 mixed crystal has been investigated in the range of Pb 2+ composition between 20 mol% and 40 mol%. The spectrum consists of a band of free exciton luminescence near the absorption edge and a band with large Stokes-shift. Temperature and excitation energy dependences of the spectra and decay profiles of the luminescence indicate that the low energy band originates from self-trapping of excitons in the clusters. Stability between the free and self-trapped exciton states is governed by the exciton band width which depends on the size of clusters.