Fabrication and Luminescence Caracterization of Rare Earth Phosphors for X-ray Imaging

by Myeongjin Oh (Ph.D Candidate)

Friday May 12, 2017, 2:00 PM → 3:00 PM Asia/Seoul

201-4호 (제1과학관)

The purpose of this study is to develop the novel phosphor for medical radiographic imaging, such as digital radiography (DR), X-ray imaging plate (IP) and intensifiers etc. Besides, the phosphor can be used various industrial fields, such as various lamps, plasma display, laser materials, cathode-ray tubes and non-destructive inspection and etc. 
In this experiment, the novel phosphors such as Eu3+ or Sm3+ doped Lithium Lutetium Borate; LLBO (Li6Lu(BO3)3), Ln3+ doped Gd2GeO5, Eu3+ or Ce3+ doped Gadolinium Gallium Aluminum Garnet; GGAG (Gd3Ga2Al3O12) and Gd3+ doped Lithium Yttrium Borate; LYBO (Li6Y(BO3)3) are fabricated. These raw materials made up of rare earth elements have a high effective Z-number (Zeff) in comparison to other phosphors and the high effective Z-number led to the high absorption efficiency for X-ray or gamma rays in medical radiation imaging fields. 
Most of phosphor are synthesized by solid state reaction with high purity of the host and activator materials at high temperature by using electric furnace. Then, the luminescent properties of the phosphor were characterized by photoluminescence, X-ray induced luminescence, proton induced luminescence, decay time, relative light yield, X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) measurements. 
The emission spectra of fabricated phosphors show the long wavelength at 500~700 nm roughly. The long wavelength is well matched to silicon based light sensor such as photo diode (PD), charge coupled devices (CCDs), thin film transistor (TFT) and complementary metal oxide semiconductor (CMOS) sensor because of their high quantum efficiency compared to the photomultiplier tube (PMT) and another light detectors. Therefore fabricated phosphors are suitable for X-ray imaging application using CCD, CMOS, PD or TFT which is the high quantum efficiency in the wavelength range of 500~700 nm. 
The relative light yield is one of the most important parameter to determine the characteristic of phosphor. As a result, GGAG (Gd3Ga2Al3O12) and LLBO (Li6Lu(BO3)3) phosphor shows the high effective light compared to reference phosphor such as Gadox (Gd2O2S:Tb).

Thesis Advisor: Prof. Hongjoo Kim