Preparation And Properties Of The (Y,Gd)₂O₃:Eu³⁺ Scintillation Ceramic Powders

Scintillator is widely used in the detection equipments of high energy physics, nuclear medicine and geological exploration areas as a photoelectric conversion device. Presently, the commonly used scintillation material is single crystal which needs high requirement for the equipment and has the long prepare period and high cost. Compared to single crystal, the polycrystalline ceramic scintillator is becoming a new research focus because of its low cost and good processing performance and its properties are easy to tailor. The performance of (Y,Gd)₂O₃:Eu³⁺ transparent ceramic scintillator meets requirements of the CT scintillation material, and it has the merits of uniform doping compared with single crystal scintillator. The synthesis of excellent scintillation powders is one of the key technologies which need to resolve during the preparation of ceramic scintillator.The preparation technology and performance of (Y,Gd)₂O₃:Eu³⁺ scintillation ceramic powders were studied in this paper emphatically. The microemulsion and sol-gel methods were used to prepare (Y,Gd)₂O₃:Eu³⁺ nanopowders. The phase transformation, crystallization process, particle size, morphology, suitable pH value and photoluminescence properties of the sample were characterized by XRD, TG/DSC, SEM, TEM and PL.(1) (Y,Gd)₂O₃:Eu³⁺ nanoparticles were prepared by reverse microemulsions method. Results show that the grain size increases with the rising of crystallization temperature and the complete crystallization temperature of the precursor is 800℃. Morphology of the samples prepared with different initiate concentration was received. Particle is near-spherical with the primary size of 20nm when the initiate concentration is 0.37M. The excitation spectra of (Y,Gd)₂O₃:Eu³⁺ samples are observed monitoring at 612nm, and there is a wide band between 230 to 250nm which is due to the charge transfer band (CTB) of Eu³⁺-O^2-. The characteristic peak of the sample locates at 612nm which is caused by ⁵D₀-⁷F₂ transition of Eu3+. When the atomic content of Eu is above 10%, the concentration quenching occurrs which leads to the intensity of the characteristic peak decreased. (2) During the preparation of (Y,Gd)₂O₃:Eu³⁺ nanoparticles by sol-gel method using citric acid as the chelating agent, the behavior of solid solution and luminescence properties of (Y,Gd)₂O₃:Eu³⁺ particles were studied. The results show that the appropriate condition to prepare cubic (Y,Gd)₂O₃:Eu³⁺ powders is the pH value less than 3, calcining temperature 900℃and time 2 h. (Y,Gd)₂O₃:Eu³⁺ powder with spherical morphology and size of 50nm can be prepared under the condition of pH = 1, initial solution concentration is 0.3mol/L and adding a little amount of glycol (5% volume fraction). Luminescence properties of the powder are affected by the ratio of Y, Gd and the content of Eu. The luminous intensity reaches the maximum value when the powder composition is (Y_0.1Gd_0.9)₂O₃:Eu³⁺ and the content of Eu is 7.5% (atomic fraction). Above 7.5%, concentration quenching occurs and the emission intensity decreases.Both microemulsion and sol-gel method can be used to prepare near spherical (Y,Gd)₂O₃:Eu³⁺ nanoparticles with narrow size distribution and the particle size is about 20 and 50nm respectively. Powders prepared by microemulsion have better luminescence than that by sol-gel which is due to the smaller particle size.