ABSTRACT
This chapter provides a review on the scintillators improved by the methods based on the principles of nanophotonics. The main contents contain the enhanced light extraction efficiency of scintillator by photonic crystals, the controllable directivity of emission from scintillators by photonic crystals, and the fast decay component of scintillators by surface plasmon polariton with metal nanoparticles. The application of nanophotonics on scintillators will significantly promote the development in the field of radiation detection in a totally new way. In this chapter, the basic principles are described in detail and the experimental demonstrations are summarized. 7.1 Introduction to ScintillatorsIn 1896, the earliest scintillator CaWO4 was discovered followed by the discovery of X-ray by Röentgen.1 In the 1940s, the modern radiation detection system emerged due to the development of
the photomultiplier tube and the discovery of NaI:Tl scintillator, which is the most typical scintillator. Scintillators can be defined as materials that absorb incident particles (such as electrons, protons, neutrons, a-particle) or high-energy photons (such as X-ray, g-ray) and subsequently convert the deposition energy efficiently into a large number of photons in the visible or ultra-violet range, which can be directly detected by photomultipliers, photodiodes or CCD.2 In this way, the energy, position, and time of the incident radiation can be efficiently determined. Therefore, scintillators play an important role in radiation detection systems with various applications in nuclear medical imaging, high-energy physics experiments, nuclear physics experiments and national security areas.The nature of scintillation process is the spontaneous emission under the excitation of ionizing radiation. The physical processes involved in scintillation can be divided into three stages. The first stage is the ionization event, which creates inner shell holes and primary electrons by the interactions of photoabsorption, Compton scattering, and electron-positron pair formation. The second stage is the thermalization of hot electrons and holes until the energy becomes less than the ionization threshold. The carries diffuse in the lattice and, subsequently are trapped on defects and impurities. This process can lead to the excitation of the luminescence centers. The last stage is the luminescent process. The excited luminescent center returns to the ground state by emitting a photon or nonradiative transition. In general, an ideal scintillator should have the following properties: high light yield, short decay time, high density, no afterglow, good spectral match to photo detectors, good chemical stability and mechanical strength, and low cost.3
