Study On Application Of Enhancing The Light Output Of Scintillator Based On Micro-nano Fabrication

Scintillator, one of the important material for ionizing radiation detection, convertsinvisible particle or electromagnetic photon into a large amount of photons of muchlower energy in the near visible or visible range, which can be detected byphotodetectors directly. Having the advantages of high light yield, high stopping power,modest decay time and good radiation hardness, inorganic scintillators are widely usedin high energy particle detection, astrophysics, medical imaging and non-destructiveinspection.Light output is the most frequently considered characteristic of scintillators, withwhich energy resolution, time resolution and detection efficiency of detection systemare correlated. In the field of radiation imaging, improvement in light output is requiredto enhance the detection sensitivity and to lessen radiation damage on samples andpatients. One of the problems is that approximately50%of the generated photons areconfined inside the scintillator owing to total internal reflection at its exit surface,arising because of the large refractive index difference between scintillator and air. Inorder to overcome this problem, researchers have tried to change the geometryconfiguration of scintillator, to couple the scintillator with optical grease of highrefractive index and to increase surface roughness. Patterning scintillator with photoniccrystals is a newly developed technique to enhance the light extraction efficiency bythe modification of light propagation. It is superior to the conventional methods sincethat it can break the total internal reflection condition and achieve a broadbandenhancement. In addition, photonic crystals can tailor the direction of light extraction,thereby increasing the light outcoupling in preferred directions. It is also an efficientway because optimal structural parameters of photonic crystal for a specific scintillatorcan be obtained by simulation.Previous studies mainly dealed with fundamental issues such as the he principleof light extraction and the optimal structural parameters of photonic crystal. Photoniccrystal has not been utilized in imaging detector to investigate its effect on theperformance of detector. Meanwhile, increase in light output is necessary forscintillator-based synchrotron radiation hard X-ray imaging system to obtain in-situ,three-dimensional and dynamic images of samples. Therefore, study has been conducted to explore the possibilityof the photonic crystal’s application in synchrotronradiation hard X-ray imaging detector by performing imaging experiments withdifferent photonic-crystal-enhanced scintillators at BL13W1beamline of the ShanghaiSynchrotron Radiation Facility.Comparative study on photonic crystals prepared by different micro-nanofabrication techniques has been carried out. Overall, light output was improved, thehighest enhancement ratio of which was up to100%, while the spatial resolution wasdegraded. Additionally, the results indicate that photonic crystal with homogeneousstructure can achieve better spatial resolution, and triangular lattice photonic crystalperforms better than the square lattice one in imaging performance. Enhancement ofdetection efficiency was hard to accomplish when there was50%decrease in imagingcontrast and65%increase in light output.Potential ways to improve detection efficiency have been investigated by makingsome changes on the photonic crystal made of silicon nitride. Higher spatial resolutioncould be achieved by changing the lattice type and the location of photonic crystal, andincreasing the depth of photonic crystal could yield a higher light output.