Photoluminescence lifetime studies of PbI2 nanoclusters and microcrystallites in Pb0.30Cd0.70I2 alloys

One of the important parameters of devices developed on the basis of semiconductor materials is a fast response, which greatly determines their performance. In this case, emission with different lifetimes may arise depending on the crystalline structure of the materials being studied. Here, the photoluminescence (PL) decay kinetics of different recombination processes in novel Pb0.30Cd0.70I2 nanoscintillator materials were studied. This allowed us to obtain the lifetime distributions for different recombination processes. It is shown that the exciton lifetime ranges from tens of picoseconds for free excitons in large PbI2 nanoclusters of submicron size (microcrystallites) to hundreds of nanoseconds for self-trapped excitons (STEs) in small nanoclusters. It was found that the lifetime distribution of donor-acceptor pairs depends on their emitted energy and corresponds to the microsecond range. The presence of two peaks in the lifetime distributions for STEs, which are formed at the stretching Pb–I bond on the nanocluster surface, may be associated with the formation of bright and dark STE states in small PbI2 nanoclusters. It was shown that the bright STE states largely determine the intensity of the PL spectra of Pb0.30Cd0.70I2 alloys both at low temperature and at room temperature. The peak of the lifetime distribution for these excitons corresponds to 33.4 ns. This indicates that the emission of the Pb0.30Cd0.70I2 alloys, determined by these states, is fast. The effect of nonradiative recombination on the lifetimes of excitons in PbI2 nanoclusters and microcrystallites was also studied. Our findings provide a way to develop novel fast nanoscintillator materials based on Pb0.30Cd0.70I2 alloys that are suitable for biomedical and industrial imaging applications.