All-inorganic copper-halide perovskites for large-Stokes shift and ten-nanosecond-emission scintillators

Abstract

The recent surge of interest in low-dimensional lead-free copper halide perovskites (CHPs) has driven significant progress in optoelectronics and scintillating materials. However, the development of green-based synthetic routes for CHPs, aimed at creating fast-decaying scintillators with ultrasensitive X-ray detection, remains elusive. In this study, we utilize a mechanochemical method to obtain 1D CHP (CsCu₂I₃) and 0D CHPs (Cs₃Cu₂X₅ (X = I, Br)) focusing on the mixing of I and Br anions with different molar ratios (I : Br = 4 : 1 and 3 : 2). CsCu₂I₃ and Cs₃Cu₂I₅ exhibit a substantial large Stokes shift (SS) of 1.75 ± 0.02 eV and 1.57 ± 0.05 eV with the former displaying the absence of afterglow, whereas the latter has a deep trap of ∼500 meV, complicating the scintillation mechanism and resulting in a slower decay component. The CsCu₂I₃ scintillation decay time is primarily characterized by a fast component (τ₁) of 9.30 ± 0.01 ns, accounting for contribution (C₁) of 43% from the total emission. This fast decay component of ∼10 ns has not been previously reported in the family of CHPs. Similarly, τ₁ of 10.9 ± 0.6 ns is obtained in Cs₃Cu₂I₅, but when compared to its counterpart, C₁ is only 3%. Upon increasing the Br substitution in Cs₃Cu₂I₅, we observe that the traps become shallower, with energies ranging from 208 ± 21 to 121 ± 18 meV, along with an appreciable trap concentration of ∼10⁴. The C₁ of τ₁ also increases with higher Br concentration, reaching a maximum value of 29%. Unfortunately, this increased contribution in decay times is accompanied by a decrease in light yields (Cs₃Cu₂I₅ has 16.5 ph per keV at room temperature (RT)) as thermal quenching processes predominate throughout the entire series of CHPs at RT. Our work provides valuable insights into the tunable structure–property relationship through the I : Br composition ratio of CHPs, hence advancing scintillation performance by rational design towards timing applications.