X-ray detectors with high performance, durability, and flexibility detectors are required for a wide range of applications in several fields, such as medical treatment (imaging, diagnostic radiology, etc.), nondestructive testing (radioscopic inspections, radiography testing, etc.), security and defense (luggage/body scanning systems, paper mail, etc.), nuclear and radiation industries (nuclear power plants, research reactors, users of nuclear gauges, etc.), and scientific research and development. [1]-[9] Thereof, indirect X-ray detectors are widely used for ordinary flat panel X-ray detection, among which scintillator is the most important factor affecting the detection performance. [10][11][12][13][14] Currently, the ideal scintillator should meet the following basic conditions: (i) good stopping power and excellent radiation absorption, [15]-[18] (ii) high photoluminescence (PL) with large Stokes shift and radioluminescence (RL) intensity, (iii) nontoxicity with environmentally stable, [19] (iv) easily manufactured and extendable to large-area flexible applications. [20,21] Among all, inorganic copper (I)-based metal halide semiconductors meeting all the above requirements are considered as promising candidates. In particular, zero-dimensional (0D) cesium copper chloride, Cs 3 Cu 2 Cl 5 , shows excellent photoelectric performance in ultraviolet photodetectors. [22] With isolated [Cu 2 Cl 5 ] 3dimers and Cs + ions, Cs 3 Cu 2 Cl 5 is expected to exhibit intriguing optical properties mainly derived from self-trapped excitons (STEs). Different from the narrow and rapid emission of free excitons and inter-band recombination, the emission of STEs is featured with broad spectra and large Stokes shifts. Generally, the STEs emission that occurs in Cs 3 Cu 2 Cl 5 originates from structural deformation of [Cu 2 Cl 5 ] 3− dimers. [23] At the time of photoexcitation, the Cu-Cl bonds elongate (shrink) on the equatorial plane but shrink (elongate) in the axial direction, which in turn causes the local structure change from a high symmetry to a low symmetry configuration.To further improve its photophysical characteristics, the diversified structural optimization in Cs 3 Cu 2 Cl 5 could offer deeper insights and more controlling knobs on STEs emission.
Zero-dimensionalCs 3 Cu 2 Cl 5 exhibits intriguing optical properties, which can meet the basic requirements of ideal scintillator application. Here, green emitter Cs 3 Cu 2 Cl 5 nanosheets are successfully synthesized, and by doping with 2% potassium (K + ), their photoluminescence quantum yield (70.23% to 81.39%), radioluminescence intensity, and stability are improved. Further experimental and theoretical studies point out that: (1) K + brings the neighboring [Cu 2 Cl 5 ] 3− dimers groups closer, leading to lattice shrinkage and lower lattice constants; (2) such compact crystal structure results in stronger exciton-photon coupling and reduced phonon-electron coupling strength, which is beneficial to form self-trapped excitons and enhanced luminescence; (3) lower lattice ...