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Bombardment of materials by high-energy particles often leads to light emission in a process known as scintillation. Scintillation has widespread applications in medical imaging, x-ray nondestructive inspection, electron microscopy, and high-energy particle detectors. Most research focuses on finding materials with brighter, faster, and more controlled scintillation. We developed a unified theory of nanophotonic scintillators that accounts for the key aspects of scintillation: energy loss by high-energy particles, and light emission by non-equilibrium electrons in nanostructured optical systems. We then devised an approach based on integrating nanophotonic structures into scintillators to enhance their emission, obtaining nearly an order-of-magnitude enhancement in both electron-induced and x-ray–induced scintillation. Our framework should enable the development of a new class of brighter, faster, and higher-resolution scintillators with tailored and optimized performance. Description Scintillating nanophotonics When a high-energy particle collides with a material, the energy is transferred to atoms in the material, and light can be emitted. This scintillation process is used in many detector applications ranging from medical imaging to high-energy particle physics. Roques-Carmes et al. integrated scintillating materials with nanophotonic structures to enhance and control their light emission (see the Perspective by Yu and Fan). The authors show how nanophotonic structures enable the ability to shape the spectral, angular, and polarization characteristics of scintillation. This approach should enable the development of brighter, faster, and higher-resolution scintillators. —ISO Integrating scintillating materials with nanophotonic structures can enhance and control light emission. INTRODUCTION Bombardment of materials by high-energy particles often leads to light emission in a process known as scintillation. Scintillators, being broadly applicable to the detection of ionizing radiation, have widespread applications, including in x-ray detectors for medical imaging and nondestructive inspection, gamma-ray detectors for positron emission tomography, phosphor screens in night vision systems and electron microscopes, and electromagnetic calorimeters in high-energy physics experiments. Accordingly, there is great interest in the development of “better scintillators” with greater photon yields and improved spatial and energy resolution. Better scintillators in general would lead to definite improvements in all of the above use cases. One example application is medical imaging, where brighter scintillators could enable very-low-dose x-ray imaging, therefore reducing potential harm to patients. Most research into the problem of improving scintillators involves the synthesis of new materials with better intrinsic scintillating properties. RATIONALE The conversion of a high-energy particle into photons is a complex, multiphysics process in which the incident particle creates a cascade of secondary electron excitations in the scintillator. These secondary excitations then relax into a non-equilibrium distribution before emitting scintillation photons. By creating spatial inhomogeneities in the scintillator on the scale of the scintillation photon wavelength, and thus modulating the optical properties of the material on the wavelength scale, one can control and enhance the light emission. In such “nanophotonic scintillators,” it is then possible for the light-emitting electrons in the scintillator to emit light much more rapidly due to enhancement of the local density of optical states available to the electrons for light emission. It is also possible to use these nanophotonic structures to “steer” trapped light out of the scintillator, enabling more light to be detected. Both of these effects lead to enhanced rates of scintillation photon emission. These nanophotonic effects are material-agnostic, enabling in principle any scintillator to be enhanced, and these effects can also be in principle observed for any type of high-energy particle. RESULTS We developed a first-principles theory of nanophotonic scintillators, taking into account the complex processes leading to electron excitation as well as the light emission by non-equilibrium electrons in arbitrary nanophotonic structures. Using the theory as a guide, we experimentally demonstrated order-of-magnitude scintillation enhancements in two different platforms: electron-induced scintillation by silica defects, and x-ray–induced scintillation by rare-earth dopants in conventional scintillators. The enhancements in both cases were enabled by two-dimensionally periodic etching of either the scintillator or the material above the scintillator to create a two-dimensional photonic crystal slab geometry. The theory accounted for the enhancements observed experimentally, as well as other effects that required first-principles description of the underlying microscopic kinetics of the emission process. For example, we could explain the observed spectral shaping as a function of geometrical parameters of the photonic crystal slab. Additionally, using the framework, we could account for nonlinear relationships of the signal on the incident particle flux, as well as effects where the dominant scintillation wavelength could change as a function of high-energy particle flux. Beyond, we used a nanopatterned x-ray scintillator to record x-ray scans of various specimens and observed an increase in image brightness. This directly translates into faster scans, or equivalently a lower x-ray dose required to achieve a given brightness. CONCLUSION Our framework can be directly applied to model nanophotonic scintillation in many existing experiments, accounting for arbitrary types of high-energy particles, scintillator materials, and nanophotonic environments. Beyond this, our framework also allows the discovery of optimal nanophotonic structures for enhancing scintillation. We show how topology optimization and other types of nanophotonic structures can be used to find structures that could present even larger scintillation enhancements. We expect that the concept demonstrated here could be deployed in all of the application areas where scintillators are used, with compelling applications throughout, including medical imaging, night vision, and high-energy physics experiments. Nanophotonic scintillators. (A) Nanophotonic scintillators consist of nanophotonic structures integrated with scintillators. Scintillation can be modeled, tailored, and optimized by combining energy loss dynamics, occupation level dynamics, and nanophotonics modeling. (B) Order-of-magnitude x-ray scintillation enhancement with a photonic crystal nanophotonic scintillator. (C) X-ray scan taken with a nanophotonic scintillator (white dashed square).