Preparation And Characteristics Of Bahfo₃:ce Ceramic Scintillator Powders

Scintillating material is a kind of functional material which can radiate visible or ultraviolet light after absorbing a high-energy particles. Scintillation probe which is constituted with scintillator and photomuitplier is the key component of the imaging device. It can be widely used in the fields of imaging of nuclear medicine, nuclear physics, high-energy physics, industrial CT, oilwell exploration, safety inspection, etc. Since barium hafnate, being an optical isotropic(cubic) compound with the perovskite-type oxides crystal structure, can be processed into transparent ceramic bodies. Moreover, high density and atomic number make BaHfO3 an attractive host material for scintillators with high stopping power. Ce3+cation have high luminous intensity and fast decay as the 5dâ†'4f transitions. BaHfO3:Ce is a novel ceramic scintillator, because of the emission peak wavelength of the BaHfO3:Ce is suitable for the photomultiplier tube and silicon photo diode.In this paper, the preparation technology and characteristics of BaHfO3:Ce powders were studied systematically. The hydrothermal process and solid-state reaction process were used to prepare BaHffO3:Ce nanopowders. The phase transformation, crystallization process, morphology characteristics, partice size and photoluminesecence properties of the samples were characterized by XRD, SEM, TEM and PL.BaHfO3:Ce powders were synthesized by hydrothermal process. The result shows that BaHfO3:Ce can be directly synthesized by hydrothermal process without calcination. And the BaHfO3:Ce powders which are 0.5-1μm in size and polygonal morpholoty can be synthesized while the mol ratio of Ba/Hf is 1.1:1, the pH value being higher than or equal to 13, the temperture of hydrothermal reaction being 200℃and the 24 hrs reaction time. It also shows that the morphology can be controled by regulating the pH. With the pH value increased, the crystal morphology have a gradual transition from the slender needle shaped to granule. The polygonal morpholoty powders can be obtained while the pH vaule is 13.5. As the soaking time become longer, the crystal morphology of the powders is close to complete and regular. The excitation spectrum of BaHfO3:Ce nanoparticles has two excitation peaks separately at 396 nm and 446 nm points. The emission spectrum excited by the 396 nm light consists of two emission bands, peaking at 531 nm and 591 nm, respectively, the emission character of which changes from 5dâ†'2F5/2 to 5dâ†'2F7/2 transitions of Ce3+ cation. When the emission spectrum is excited by the 446 nm light, only one wide emission peak at 591 nm point exists and the other one at around 531 nm becomes flat. The luminescence intensity of powders depends on different morphologies.BaHfO3:Ce nano-powders were synthesized with different Hf precursors by the process of solid-state reaction. The behavior of solid solution and luminescence properties of BaHfO3:Ce particles were studied. The result shows that there are differences in both synthetic temperature and luminescence properties with different Hf precursors. The average diameter of the BaHfO3:Ce nano-powders synthesized with high activity Hf(OH)4 and BaO is about 30 nm, and the powders being approximate to spherical morphology have good crystallinity and dispersibility after calcining at 1100℃for 2 h. It also shows that there is no change happened on the cubic crystal structure even though a little amount of Ce3+ion added to the powders can lead to the lattice distortion of BaHfO3 matrix material.When the Ce3+dopant content is 0.9% (molar fraction), the figure of the emission peak reaches its highest point. This figure, however, drops when the Ce3+dopant content is 1.1%(molar fraction), which is resulted from the concentration quenching. The luminescence intensity of powders also depends on the both affects of crystallinity and morphology. The powders with high crystallinity, uniform size, approximately spherical morphology and good dispersibility have the optimal luminescence intensity.The diameter of the powders synthesized by hydrothermal process is micron-sized and the morphology can be controled. The partical size of the powders prepared by solid-state reaction process is nanometer and the powders are approximate to spherical morphology. Powders prepared by solid-state reaction process have better luminescence than that by hydrothermal process.