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 degreesC for 18 to 137 h. It has been found that the relative concentr ations of different aggregates depend on thermal treatment conditions. Thei r optical characteristics obtained at 4.2-300 K have been compared with the corresponding characteristics of CsPbI3 and Cs4PbI6 single crystals as wel l 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 b ands peaking at 465, 535 and approximate to 600 nm have all been ascribed t o the CsPbI3-type aggregates dispersed in a CsI single crystal matrix. The emission band peaking at 435 nm and the corresponding excitation bands at 3 62 and 288 nm have been ascribed to the Cs4PbI6-type aggregates. The mechan ism of the creation of aggregates in a CsI:Pb crystal has been discussed.