TADF-Based X-ray Screens with Simultaneously Efficient Singlet and Triplet Energy Transfer for High Spatial Imaging Resolution

Abstract

X-ray imaging scintillators play a crucial role in medical examinations and safety inspections, making them an essential technology in our modern lives. However, commercially available high-performance scintillators are fabricated exclusively from ceramic materials that require harsh preparation conditions and are costly to produce. Organic scintillators have emerged as a promising alternative due to their transparency and ease of fabrication at a low cost. Unfortunately, organic scintillators suffer from inefficient exciton utilization efficiency, leading to poor performance in X-ray imaging screens and hindering their commercialization. In this study, we explore the use of thermally activated delayed fluorescence (TADF) chromophores (4CzIPN-I and 4CzTPN) to enhance the absorption of ionizing radiation in X-ray imaging screens by an order of magnitude. By leveraging the unique features of TADF chromophores through simultaneously singlet− singlet and triplet−triplet efficient energy transfers at the interface between two different TADF systems, we demonstrate an impressive X-ray sensitivity and radioluminescence intensity. Our time-resolved experiments and density functional theory (DFT) calculations provide further evidence for the effectiveness of this approach. The resulting X-ray imaging screens based on this efficient interfacial energy transfer process in TADF systems exhibit outstanding X-ray imaging resolution of 20 line pairs/mm, the highest resolution reported thus far for organic scintillators. This resolution is at least two times higher than that achieved by commonly used commercial inorganic scintillators in the X-ray imaging market. These findings introduce a new component for greatly improving the performance of organic X-ray imaging scintillators, supporting a wide range of emerging X-ray applications with exceptional spatial resolution.

Bulk Organic Doped p-Terphenyl Crystals for X-ray Scintillators with Low Detection Limit, Nanoseconds Decay Time, and Tunable Fluorescence

“…Results reveal a gradual decrease in the HOMO–LUMO energy gap for p -terphenyl, chrysene, picene, anthracene, tetracene, and pentacene, consistent with the corresponding characteristic emission wavelengths of pure crystal and doped crystals (Figure a). The overlapping HOMO–LUMO energy levels between the host molecule and dopants suggest a possible energy transfer process, where the host molecule acts as an X-ray sensitizer and the dopants serve as luminescent centers . Furthermore, by comparison of the XEL spectra of the host molecule with the ultraviolet–visible absorption spectra of the dopant molecule (Figure S7), an overlap between the two can be observed, thus confirming the presence of an energy transfer process.…”

Designing thermally activated delayed fluorescence emitters with through-space charge transfer: a theoretical study

“…19–23 TADF molecules with through-bond charge transfer (TBCT) properties have been synthesized by constructing π-conjugated donor–acceptor (D–π–A) molecular structures. 24–27 Furthermore, the non-planar configuration can weaken intermolecular stacking interactions, suppressing the quenching effect due to aggregation. 28 However, the twisted molecular configuration reduces the overlap integral, resulting in a smaller fluorescence oscillator strength and lower fluorescence efficiency.…”

Surfactant-Assisted Synthesis of Hybrid Copper(I) Halide Nanocrystals for X-ray Scintillation Imaging

“…Radiation detection to convert high-energy photons into low-energy photons has received extensive attention in medical diagnostic technology, safety detection, computer tomography, etc. − The mainstream indirect conversion method is to convert X-rays into light by using scintillators . However, commercial scintillators face the problems of a complicated preparation process with high-temperature crystallization above 1700 °C, − which squeezes the area of the application of these materials.…”