Luminescence and Charge Trapping in Cs₂HfCl₆ Single Crystals: Optical and Magnetic Resonance Spectroscopy Study

Abstract

Single crystals of the undoped Cs 2 HfCl 6 were grown using the vertical Bridgman method. Photoluminescence spectra and decays were measured in the extended temperature range of 8−500 K and approximated by a phenomenological model. Self-trapped exciton and defect-related emissions were clearly distinguished with the onset of thermal quenching above the room temperature. Electron paramagnetic resonance experiment revealed the formation of two configurations of V k center (Cl 2 − molecular ion) at low temperatures. One of the V k centers is created by a hole self-trapping at two neighboring Cl ions. In the temperature range 70−80 K, this state is thermally disintegrated and reappears in another configuration formed most probably by an interstitial Cl ion (an analog of the H-type center in alkali halides).

Hydrogen Bonding and Broad-Band Emission in Hybrid Zinc Halide Phosphors

“…-type centers to be responsible of the broad band emission in Rb 2 ZnCl 4 and K 2 ZnCl 4 but were not able to confirm their hypothesis 22. V k centers have also been identified in other metal halides such as Cs 2 HfCl 6 23. …”

Novel Cs2HfCl6 Crystal Scintillator: Recent Progress and Perspectives

“…Because of a hint on the existence of two different V k centers, one created by the self-trapping of a hole at two regular chlorines forming the Cl 2− molecular ion in the Cs 2 HfCl 6 , and seeking for more details, authors in [38] performed studies by using correlated measurements of EPR, thermo-stimulated luminescence (TSL), and radioluminescence (RL) techniques to evaluate the influence of the material stoichiometry on the irradiation-induced defects, their types, as well as quantity and emission centers.…”

“…The cylindrical shape of the as-grown Cs 2 HfCl 6 crystals, produced in [38], were 12 mm in diameter and (40−55) mm in length depending on the starting charge of the material. The biggest issue with produced CHC1 crystal was the stoichiometry change along the crystal axis reaching the content of 97 mol% of the Cs 2 HfCl 6 phase at the start of the crystal and only 22 mol% at the end.…”

Colloidal Synthesis and Optical Properties of Perovskite-Inspired Cesium Zirconium Halide Nanocrystals

“…The combination of large Stokes shifts and broad, asymmetric PL features suggests radiative recombination may originate from self-trapped excitons, 49 which has been reported for similar compounds such as Cs 2 HfCl 6 . 50 − 52 The lack of subgap contribution to the PLE spectrum of the Cs 2 ZrBr 6 NC thin films also indicates that radiative recombination is not due to permanent defect states. 53 The similar PLQY values of the bulk powder, NC suspensions, and NC thin films support the hypothesis that (i) the self-trapped exciton emission is intrinsic, related to the bulk, and (ii) the emission, consequently, is not strongly dependent on the crystallite size for the sizes studied here nor on its surface/volume ratio.…”