EXCITON DYNAMICS OF ORTHORHOMBIC PHASE PbI₂ EMBEDDED IN PbI₂-PbBr₂ MIXED CRYSTALS

Abstract

Reflection, time-integrated and time-resolved luminescence spectra have been measured in PbI 2(1-x) Br 2x(x≥0.5) mixed crystals in order to elucidate the excitonic properties and relaxation processes of orthorhombic phase PbI 2 embedded in the mixed crystals. The crystal structure of PbI 2(1-x) Br 2x above x=0.5 is orthorhombic and an observed new reflection peak (~2.5 × 104 cm -1) above x=0.5 is due to an excitonic state of orthorhombic phase PbI 2. On the excitation energy above 2.5 × 104 cm -1, a broad luminescence band with a large Stokes shift from the reflection peak was observed. This luminescence band is attributed to a self-trapped exciton state. The decay of the luminescence has two components. Based on an atomic excitation picture, the shorter decay component (≤10 ns ) is attributed to the allowed transition from 3P1 to 1S0. On the other hand, the longer decay component (~3 μ s ) might be due to the forbidden transition from 3P0 to 1S0.

Exciton-relaxation dynamics in lead halides

“…The tendency of the mixed ratio in the valence bands is qualitatively supported by the recent electron-spin-resonance (ESR) study manifesting self-trapping hole centers of Pb 3+ in PbCl 2 [7] and Br 2 − in PbBr 2 [8]. Mixed crystal of PbI 2(1−x) Br 2x is an example to show the variety of exciton dynamics coming from lead-halogen complex; it enables us to observe the change from FE luminescence into self-trapped-exciton (STE) luminescence by increasing the ratio of bromide ions [9]. This system implies that halogen ions add the variety in exciton dynamics and play a crucial role in realizing the localization of excitons.…”