Photo-enhanced Extraction Of Inorganic Scintillator Based On Photonic Crystal Technology

The scintillation detection system is composed of scintillators,photomultiplier tubes and electronic signal amplifier.The basic principle is that the interaction of the scintillator with rays or incident particles produces visible or near-ultraviolet scintillation light,and the scintillation light is absorbed by the photodetector to detect the rays or particles.Among them,As the core functional material in the scintillation detection system,the scintillator is widely used in nuclear medicine imaging,high-energy physics experiments,nuclear physics experiments and astrophysics.The extraction efficiency of scintillation is one of the important performance indicators of scintillator,which will affect the detection efficiency and sensitivity of scintillation detection system,and ultimately affect the four detection targets:spatial resolution,energy resolution,time resolution and particle discrimination.Because the inorganic scintillators（1.8².6）differ greatly from the air（¹.0）refractive index,the total reflection of scintillation light is easy to occur inside the scintillator,which limits most of the scintillation light to the inside of the scintillator and prevents it from being emitted into free space.Only a small part of the scintillation light is absorbed by the photoelectric detector,resulting in low detection efficiency.At present,there are many methods for overcoming total internal reflection.The more traditional method is to seamlessly add an optical coupling agent with a small difference in refractive index between the scintillator crystal interface and the photodetector.In recent years,a new method has been proposed to improve the light extraction efficiency of scintillators by using photonic crystals.In this paper,two-dimensional photonic crystals are introduced on the surface of scintillators to improve the extraction efficiency of scintillation.Two-dimensional periodic array structures are fabricated on the surface of scintillators based on self-assembly and electron beam lithography.The results are as follows.Firstly,based on the single dielectric sphere Whispering gallery modes and the diffraction effect of periodic array,single-layer SiO₂ microsphere periodic arrays were fabricated on the surface of BGO(Bi₄Ge₃O₁₂)and LYSO(（Lu,Y）₂SiO₅:Ce³⁺)scintillators by liquid-level self-assembly method.When the diameter of SiO₂microspheres were 360 nm and 300 nm respectively,the light extraction efficiency of BGO and LYSO scintillators increased by 53%and 120%,respectively.Secondly,the simulation results show that the high refractive index GaN micro-nano periodic structure is easier to improve the scintillator output efficiency.The optical extraction efficiency of BGO scintillator can be further improved by introducing a high refractive GaN conformal layer on the basis of a single SiO₂microsphere periodic array.When the GaN thickness is 70 nm,the optical extraction efficiency of BGO scintillator can be increased by 158%.Finally,the nano-periodic array of titanium dioxide was fabricated on the surface of LYSO scintillator by electron beam lithography.The theoretical optimization of the two periodic arrays was carried out.When the period,diameter and depth were 450nm,300 nm and 152 nm,respectively,and 410 nm,320 nm and 112 nm,the light extraction efficiency of LYSO scintillator was increased by 80%.The interaction between the high refractive index periodic array structure and the scintillator can bring more scintillation modes into the nano-periodic structure.These modes are coupled with the periodic structure.Because of the diffraction effect of the periodic structure,these excited modes will eventually be diffracted out,which improves the light extraction efficiency of the scintillator.