Localized excitons boost scintillation
Structural modulation increases scintillation yield by approximately 460 percent and enables low afterglow X ray imaging
image: Figure 1. Structural modulation strengthens exciton confinement in zero dimensional metal halides. The original illustration compares the structures and exciton behavior of Cs₃YCl₆ and (Cs₈Cu)Y₃Cl₁₈, together with their quenching energy barriers and scintillation yields.
Credit: Copyright © 2026 Yujie Wang et al.
Scintillators convert high energy radiation into detectable light, making them essential materials for radiation detection and X ray imaging. Yet some of the energy deposited by radiation is lost before it can be emitted as light. A study published in Research shows how restructuring the light emitting units in a metal halide can reduce these losses by confining electronic excitations more strongly.
The work was carried out jointly by the teams of Yuntao Wu at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, Martin Nikl at the FZU–Institute of Physics of the Czech Academy of Sciences, and Xiaoping OuYang at the Northwest Institute of Nuclear Technology, together with collaborating researchers. Collaborating teams developed an exciton confinement strategy through structural modulation. By incorporating copper(I) into the zero dimensional halide Cs₃YCl₆, the researchers formed (Cs₈Cu)Y₃Cl₁₈ and achieved an approximately 460 percent increase in self trapped exciton related scintillation yield relative to the parent material.
Low dimensional metal halides have attracted growing attention because their isolated structural units can confine charge carriers and support self trapped exciton emission. Excitons are formed by coupled excited electron and hole pairs, and self trapping enables their localization due to polarisation response-induced distortion of the surrounding lattice. However, high efficiency under optical excitation does not necessarily ensure high scintillation efficiency. Under ionizing radiation, interactions between excitons, or between excitons, excited charge carriers and defects, can cause energy losses and decreased light emission efficiency.
The new study builds on the team’s earlier work on confined exciton scintillators, including Cs₃Cu₂I₅ and related copper halides. It addresses a central question: can changing the structure of the emitting units strengthen exciton confinement and improve their resistance to quenching under ionising radiation excitation?
Introducing copper(I) reorganized the original [YCl₆]³⁻ octahedral units into paddle wheel shaped [Cu₂(YCl₆)₃]⁷⁻ clusters. First principles calculations showed that excitons were more strongly localized within these clusters. Temperature dependent luminescence spectroscopy and kinetic analysis also revealed a higher energy barrier for self trapped exciton quenching, supporting the role of stronger confinement in suppressing nonradiative losses.
The estimated scintillation yield increased from approximately 1,900 photons per megaelectronvolt for the self trapped exciton emission of Cs₃YCl₆ to 10,700 photons per megaelectronvolt for (Cs₈Cu)Y₃Cl₁₈. The estimates were obtained by comparing X ray excited emission with a commercial bismuth germanate reference under the same experimental conditions. The two halides have similar X ray absorption coefficients, supporting the interpretation that the improvement arises from changes in exciton behavior rather than simply stronger absorption.
The material also exhibited low afterglow, with a residual signal of approximately 0.05 percent at 10 milliseconds after the X ray source was switched off, compared with approximately 6 percent for the CsI:Tl reference in the study. Low afterglow helps limit ghost images in dynamic imaging. The researchers reported an estimated X ray detection limit of 147 nanograys in air per second under their measurement conditions.
To explore imaging applications, the team dispersed the scintillator powder in polydimethylsiloxane to prepare flexible composite screens. These achieved a spatial resolution of 14.6 line pairs per millimeter at a modulation transfer function of 0.2 and resolved internal details in test objects. A laboratory model using disposable infusion tubing demonstrated imaging of flowing barium contrast liquid. This was a proof of concept rather than a clinical examination.
In a separate demonstration conducted at 480 kelvin, approximately 207 degrees Celsius, the screen recorded the melting and shape changes of a bismuth–indium–tin alloy. These results suggest potential for dynamic X ray imaging and inspection at elevated temperatures. Further device development will need to address environmental protection, as the crystals are moisture sensitive and require handling under dry conditions.
The study establishes structural modulation as a route to stronger exciton confinement in low dimensional halide scintillators. By connecting changes in atomic structure with excited state behavior and scintillation performance, it offers guidance for designing materials that convert higher portion of the energy deposited by ionizing radiation into useful scintillation light.
The work was published in Research on April 14, 2026. Yujie Wang, Xuemin Wen, and Hongliang Shi contributed equally. Martin Nikl, Xiaoping OuYang, and Yuntao Wu are the corresponding authors.