Inorganic scintillators are commonly used as sensors for ionizing radiation detectors in a variety of applications, ranging from particle and nuclear physics detectors, medical imaging, nuclear installations radiation control, homeland security, well oil logging and a number of industrial non-destructive investigations. For all these applications, the scintillation light produced by the energy deposited in the scintillator allows the determination of the position, the energy and the time of the event. However, the performance of these detectors is often limited by the amount of light collected on the photodetector. A major limitation comes from the fact that inorganic scintillators are generally characterized by a high refractive index, as a consequence of the required high density to provide the necessary stopping power for ionizing radiation. The index mismatch between the crystal and the surrounding medium (air or optical grease) strongly limits the light extraction efficiency because of total internal reflection (TIR), increasing the travel path and the absorption probability through multiple bouncings of the photons in the crystal. Photonic crystals can overcome this problem and produce a controllable index matching between the crystal and the output medium through an interface made of a thin nano-structured layer of optically-transparent high index material. This review presents a summary of the works aiming at improving the light collection efficiency of scintillators using photonic crystals since this idea was introduced 10 years ago.

Today Time-of-Flight (TOF), in PET scanners, assumes a single, well-defined timing resolution for all events. However, recent BGO-Cherenkov detectors, combining prompt Cherenkov emission and the typical BGO scintillation, can sort events into multiple timing kernels, best described by the Gaussian mixture models. The number of Cherenkov photons detected per event impacts directly the detector time resolution and signal rise time, which can later be used to improve the coincidence timing resolution. This work presents a simulation toolkit which applies multiple timing spreads on the coincident events and an image reconstruction that incorporates this information. A full cylindrical BGO-Cherenkov PET model was compared, in terms of contrast recovery and contrast-to-noise ratio, against an LYSO model with a time resolution of 213 ps. Two reconstruction approaches for the mixture kernels were tested: 1) mixture Gaussian and 2) decomposed simple Gaussian kernels. The decomposed model used the exact mixture component applied during the simulation. Images reconstructed using mixture kernels provided similar mean value and less noise than the decomposed. However, typically, more iterations were needed. Similarly, the LYSO model, with a single TOF kernel, converged faster than the BGO-Cherenkov with multiple kernels. The results indicate that the model complexity slows down convergence. However, due to the higher sensitivity, the contrast-to-noise ratio was 26.4% better for the BGO model.

The extraction of scintillation light from an inorganic scintillator is one of the major bottlenecks in Time-of-Flight Positron Emission Tomography (ToF-PET) because it directly affects the energy and time resolution of the gamma detector. To increase the light extraction efficiency, we use photonic crystal slabs (PCS), defined as thin dielectric layers structured with a 2D, or 3D, periodic pattern. A higher light output, combined with a reduction of the average path length traversed by the photons in the crystal before extraction, leads to a more precise evaluation of the particle time detection. This also implies a better coincidence time resolution (CTR). These improvements translate to ToF-PET reconstructed images with a higher signal to noise ratio and lead to more accurate diagnoses, faster exams, and possibly a reduced patient radiation dose. In this paper, we present results obtained using LYSO samples patterned with nano-imprinted PCS. Comparative Light yield (LY) measurements show an improvement of a factor 1.68 for a naked configuration, whereas coincidence time resolution (CTR) goes from 535 ps to 315 ps.

This article presents the timing performance of materials with fast light emission, tested as Minimum Ionizing Particle detectors using 150 GeV hadron beams in Monte Carlo simulations and at the CERN SPS North Area. Pixels of cross-section 2 × 2 mm² or 3 × 3 mm² and length of 3 or 10 mm were coupled to Hamamatsu SiPM and read out by fast high-frequency electronics. Materials whose timing performance relies on Cherenkov emission, namely BGSO, PWO, and PbF₂, achieved time resolutions in the range 24–36 ps. Scintillators as L(Y)SO:Ce, GAGG, and BaF₂ reached below 15 ps, the best topping at 12.1 ± 0.4 ps. These fast materials are compared to LYSO and their additional benefit is discussed. Given the promising results of BaF₂, the study is completed with measurements of the scintillation properties of a set doped with yttrium to quench the slow light emission.

Chromatic calorimetry introduces a novel approach to calorimeter design in High Energy Physics (HEP) by integrating Quantum Dot (QD) technology into traditional homogeneous calorimeters. The tunable emission spectra of QDs provide new possibilities for energy reconstruction and potentially improved particle identification in homogeneous devices. This paper presents the initial conceptual design of a chromatic calorimeter aimed at validating the feasibility of QD-based chromatic calorimetry. The study evaluates its expected performance through detailed simulations, comparing the results to the existing calorimetric technologies. By embedding QDs with distinct emission properties within scintillators, we aim to improve both timing resolution and longitudinal segmentation, thus opening new avenues for precision measurements in future HEP experiments. While further development and validation are required, QD-enhanced detectors may represent a viable option for future HEP experiments, providing an additional tool for addressing the evolving demands of particle detection.