Nanocomposites and nanomaterials 

Pb1-XCdXI2 nanocomposite scintillator material: luminescence nature and kinetics
Bukivskii A.P.1*, Gnatenko Yu.P.1, Bukivskii P.M.1, Piryatinski Yu.P.1, Fesych I.V.2, Lendel V.V.2
1Institute of Physics, NAS of Ukraine, Kyiv, Ukraine.
2Taras Shevchenko National University of Kyiv, Kyiv, Ukraine.
E-mail: ap.bukivskii@gmail.com

The investigation of physical backgrounds for development of highly sensitive high-speed non-cooled radiation scintillator materials is one of the urgent tasks of the condensed-matter physics today. PbI2 bulk crystals are known to be a highly promising material for developing fast and effective scintillators, which, however, require cryogenic cooling in order to be effectively used.
In our previous works we showed that alloying PbI2 crystals with CdI2 layered crystals leads to the manifestation of intense photoluminescence (PL) and X-ray luminescence (XRL) in such crystals at room temperature.
In this study we present the results of an investigation of the formation mechanisms of excited states of various nature, their dynamics, and the kinetics of radiative recombination in Pb1‑XCdXI2 heterogeneous semiconductor alloys upon excitation by visible and X-ray photons.
During the formation of PbCdI2 alloy, PbI2 clusters and nanoparticles are formed in CdI2 matrix. This leads to the formation of additional stable and semi-stable energy levels in PbCdI2 alloy compared to pure PbI2. Radiative recombination of such states as free and bound excitons, donor-acceptor transitions, as well as of self-trapped excitons and electrons with deep acceptor states were observed during the low temperature (4 K – 150 K) optical studies.
The room temperature optical investigation has shown that the nature of the optical transitions in Pb1‑XCdXI2 crystals at higher temperatures is determined by the presence of deep intrinsic luminescent states on the surface of PbI2 NCLs, including self-trapped excitons. The nature of the XRL of such alloys is analogous to the PL mechanisms with certain differences due to the significant difference in the energy of X-ray and visible photons. 
Based on the results of the kinetics studies of individual PL bands and their mathematical analysis, the lifetimes and the rate of recombination of the corresponding excited states were established. It was shown that the optical response of these materials is fast, and the materials, respectively, are high-speed and, accordingly, promising for the production of highly efficient, fast-acting, uncooled scintillation detectors for X- and γ-rays.