In recent years, scintillating nanoparticles have been recognized as valid potential alternatives to inorganic and organic bulk scintillators, since they meet the needs and the demanding requirements of cutting-edge applications, such as nuclear and homeland security technologies, clinical and imaging devices. Nanoscintillators feature adaptable luminescence and scintillation properties, tuned by their physical and chemical characteristics, like the electronic structure, the dimensionality, and the defectiveness [1]. Most importantly, nanoscintillators can be embedded in suitable polymeric hosts to create composite materials and produce fast, efficient, and more sensitive detectors in a cost-effective way, thanks to reduced time-consuming synthesis procedures, to meet the specific demands of all up-to-date technological and medical applications [2].

The modern research is considering scintillating nanocomposites based on lead halide perovskite (LHP) nanocrystals (NCs) for the next generation of scintillation detectors [3,4]; when embedded in polymeric matrices, LHP NCs favors the enhancement of the interaction cross-section with ionizing radiation, thanks to their high atomic number [5], and retain exceptional levels of radiation hardness [6]. The implementation of this novel class of scintillating composites is imperative and aims at the achievements of scintillators with improved performances. This goal is essentially linked to the fundamental understanding of the correlation between the physical-chemical properties and the luminescence features and to the comprehension of the scintillation mechanism in nanosystems, from the primary interaction with the ionizing radiation, through energy transfer and trapping processes, to the emission of light. A fundamental stage in the scintillation process is the transport of free carriers generated upon the interaction between ionizing radiation and the scintillating material: it is often largely affected by the presence of trapping sites, which can capture migrating charge carriers and either delay their radiative recombination or decrease the overall scintillation efficiency, according to the characteristics of the traps involved.

In this work, we disclose the role of trapping defects and their interplay with the scintillation properties of LHP NCs and nanocomposites. Specifically, we present a thorough investigation of the tight correlation existing between delayed scintillation processes and defects acting as carrier traps, as well as of the competition between trapping sites and luminescent centers in free carrier capture. To these purposes, steady-state radio-luminescence as a function of both temperature and cumulated X-ray dose is combined with time-resolved photo-luminescence measurements and wavelength-resolved thermally stimulated luminescence (TSL) at cryogenic temperatures. The performances and defectiveness of CsPbBr₃ NCs prepared by hot-injection method are investigated and compared with those of CsPbBr₃ NCs produced by ligand-assisted reprecipitation synthetic approach. Our results suggest that shallow trap states, likely related to bromine vacancies, capture and slowly release electrons via a-thermal tunnelling to spatially correlated emissive centers responsible for delayed emission: because of the relatively large concentration of such defects, electron trapping in shallow defects is the main competitive channel to radiative exciton decay. The presence of surface-related defects is common in this class of materials, although advanced strategies for their passivation are continuously improved to enhance the emission efficiency. In addition, we prove that CsPbBr₃ NCs can be effectively embedded into polymethylmethacrylate matrix to obtain a high optical quality flexible and smooth scintillating nanocomposite film, whose defectiveness resembles that of LHP bulk crystals [7], featuring isolated energetically deep defects states that trap carriers which, upon heating, recombine in a specific intragap emission center, as revealed by TSL measurements. The effectiveness of this investigation approach coupling scintillation and TSL measurements, traditionally exploited only for classical single component bulk scintillators, is therefore here demonstrated also for nanosized materials.