Halogenated Thermally Activated Delayed Fluorescence Materials for Efficient Scintillation

Abstract

Organic scintillators, materials with the ability to exhibit luminescence when exposed to X-rays, have aroused increasing interest in recent years. However, the enhancement of radioluminescence and improving X-ray absorption of organic scintillators lie in the inherent dilemma, due to the waste of triplet excitons and weak X-ray absorption during scintillation. Here, we employ halogenated thermally activated delayed fluorescence materials to improve the triplet exciton utilization and X-ray absorption simultaneously, generating efficient scintillation with a low detection limit, which is one order of magnitude lower than the dosage for X-ray medical diagnostics. Through experimental study and theoretical calculation, we reveal the positive role of X-ray absorption, quantum yields of prompt fluorescence, and intersystem crossing in promoting the radioluminescence intensity. This finding offers an opportunity to design diverse types of organic scintillators and expands the applications of thermally activated delayed fluorescence.

Halogen‐bonding boosting the high performance X‐ray imaging of organic scintillators

“…The RL intensity of organic fluorescent scintillators is positively correlated with factors of X-ray attenuation coefficient (μ∝Z 4 ), the fluorescence quantum yield (Ф f ) and the carrier trans-port efficiency (𝜂). [14,20,21] By comparing the X-ray absorption abilities of BPA and BPA-X while ignoring resonant absorption edges, [3] we observed that the X-ray absorbance follows the order of BPA-I (Z max = 53, K 𝛼 = 33.2 keV) > BPA-Br (Z max = 35, K 𝛼 = 13.5 keV) > BPA-Cl (Z max = 17, K 𝛼 = 2.84 keV) > BPA (Z max = 6, K 𝛼 = 0.278 keV), as can be seen in Figure 2a. Besides, the X-ray attenuation efficiencies also improved significantly (Figure S11, Supporting Information) and it indicates that the introduction of halogen atoms significantly enhances the Xray absorption ability of the materials, thereby leading to an improvement in the RL intensity of the materials.…”

“…Scintillators possess the ability to emit ultraviolet or visible light upon X-ray irradiation, which has garnered considerable attention in recent years due to their crucial applications in areas excitons through the heavy atom effect. Subsequently, Ma et al [13] and Wang et al [14] utilized halogen atom substitution in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene and 10-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl-9,9-dimethyl-9,10dihydroacridine thermal activated delayed fluorescence materials (TADF), respectively. Both bromine-substituted TADF molecules exhibited the highest RL intensity among the tested compounds.…”

“…Nevertheless, this strategy does not apply to organic fluorescent scintillators, as heavy atoms typically promoteISC processes, increasing the non-radiative decay rate of singlet excitons and resulting in fluorescence quenching. [14,15] By incorporating halogen atoms into the system through specific molecular design strategies, it is possible to enhance the X-ray absorption capacity while simultaneously improving the PLQY of the materials. This approach has the potential to significantly enhance the scintillation performance of organic fluorescent materials, which holds crucial importance in the development of fast-response and high-brightness organic scintillators.…”

Turning Nonemissive CsPb2Br5 Crystals into High-Performance Scintillators through Alkali Metal Doping

“…However, halide perovskites suffer from severe self-absorption due to their inherent bandgap emission, limiting their scintillation performance . Moreover, their ionic structure makes them highly susceptible to moisture-induced instability. , On the other hand, scintillators based on organic luminescent molecules or metal clusters show reduced self-absorption but lack sufficient X-ray stopping ability. , Therefore, the quest for stable scintillator materials that simultaneously address self-absorption issues and offer strong X-ray stopping power remains crucial for advancing the scintillation performance.…”

“…25,26 On the other hand, scintillators based on organic luminescent molecules or metal clusters show reduced self-absorption but lack sufficient X-ray stopping ability. 27,28 Therefore, the quest for stable scintillator materials that simultaneously address self-absorption issues and offer strong X-ray stopping power remains crucial for advancing the scintillation performance.…”