Luminescent CsPbI3 and Cs4PbI6 Aggregates in Annealed CsI:Pb Crystals

Luminescent aggregates of various types have been produced in quenched CsI:Pb single crystals by their annealing in vacuum at temperatures from 220 to 370 °C for 18 to 137 h. It has been found that the relative concentrations of different aggregates depend on thermal treatment conditions. Their optical characteristics obtained at 4.2—300 K have been compared with the corresponding characteristics of CsPbI3 and Cs4PbI6 single crystals as well as with the characteristics of CsPbI3 and Cs4PbI6-type aggregates in CsI–PbI2 thin films. The absorption band located near 411 nm and the emission bands peaking at 465, 535 and ≈600 nm have all been ascribed to the CsPbI3-type aggregates dispersed in a CsI single crystal matrix. The emission band peaking at 435 nm and the corresponding excitation bands at 362 and 288 nm have been ascribed to the Cs4PbI6-type aggregates. The mechanism of the creation of aggregates in a CsI:Pb crystal has been discussed.