Abstract
Utilizing the self-assembly method, we have successfully prepared a two-dimensional photonic crystal (PhC) of monolayer SiO2 spheres onto the Bismuth Germinate (Bi4Ge3O12, BGO) crystal and therefore supply another photonic crystal structure with the advantages of low-cost and large-area preparation to improve the light extraction efficiency of scintillator. A light extraction enhancement ratio up to 145.3% as compared the BGO coated by the PhC with the plain reference sample is observed and the underlying mechanism of scintillator light extraction is discussed in detail via a rigorous coupled-wave analysis calculation. The calculated transmission spectra and electric-field distribution exhibit the electric-field eigenmodes confined in SiO2 spheres resonating by the way of whispering gallery modes (WGMs) and becoming leaky modes due to the diffraction effect. Since almost no SiO2 nanospheres over the polystyrene spheres are immersed in preparation, we have demonstrated that the introduction of PhC structures using the SiO2 nanospheres onto the scintillator surface is an effective way to solve the light-trapping problem and therefore the design is very useful to be applied to the particle detection of radiation field.
Highlights
INTRODUCTIONBi4Ge3O12 (BGO) as an intrinsic scintillator with high internal quantum efficiency, has been extensively studied. Due to its prominent photo- and radioluminescent properties, such as low afterglow, high light yield (up to 30000 counts/MeV) and a visiblewavelength range emission spectrum (peaked at 480.0 nm) that making well matching of photomultiplier tubes (PMTs), it is so regarded as a very important scintillator for practical application in the fields of space exploration, nuclear astrophysics and medical PET imaging. In the particle detection (i.e. energy deposited and identification of particles), high light extraction efficiency that resulting in high counting statistics is vital to improve both energy and spatial resolution of the detection systems. as inorganic scintillator with high refractive index (n=2.13 at 480.0 nm), the BGO crystal suffers from serious total internal reflection (TIR) and Fresnel reflection, degrading the light extraction efficiency and hindering the implementation of BGO detectors for both the rare-event detection and counting for incoming particles with high intensity
In order to obtain a significant increase of light extraction, photonic crystal (PhC) has been widely used since it was firstly proposed in 1987.9,10 The PhC exhibits a periodic modulation of the dielectric constant and has played a key role for tailoring the emission properties in light-emitting diodes (LEDs),11 optical waveguides,12 photonic circuits
To understand the SiO2 PhC structure effect on the light extraction of BGO scintillator surface, the simulations for transmittance as a function of incident angles at 480.0-nm wavelength are shown in Fig. 2 for p-polarization light
Summary
Bi4Ge3O12 (BGO) as an intrinsic scintillator with high internal quantum efficiency, has been extensively studied. Due to its prominent photo- and radioluminescent properties, such as low afterglow, high light yield (up to 30000 counts/MeV) and a visiblewavelength range emission spectrum (peaked at 480.0 nm) that making well matching of photomultiplier tubes (PMTs), it is so regarded as a very important scintillator for practical application in the fields of space exploration, nuclear astrophysics and medical PET imaging. In the particle detection (i.e. energy deposited and identification of particles), high light extraction efficiency that resulting in high counting statistics is vital to improve both energy and spatial resolution of the detection systems. as inorganic scintillator with high refractive index (n=2.13 at 480.0 nm), the BGO crystal suffers from serious total internal reflection (TIR) and Fresnel reflection, degrading the light extraction efficiency and hindering the implementation of BGO detectors for both the rare-event detection and counting for incoming particles with high intensity. Most previous work have been done in endeavouring to improve the light extraction efficiency on the scintillator-air interface, low-cost and large-area (greater than dozens of square millimeters) photonic crystal preparations on inorganic scintillator using the methods of soft X-ray, ultraviolet nano-imprint interference lithography (XIL) or electron beam lithography is still a problem in practical detector applications. 17 and 19, periodic array of monolayer SiO2 nanospheres are firstly introduced onto the BGO crystal surface and the capability of extracting the scintillation light beyond the critical angle θc is demonstrated.
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