Investigation On The Growth And Luminescence Properties Of CdRe₂?WO₄?₄?Re=La,Gd? Tungstate Scintillator Crystals And Mixed Crystals

Tungstate scintillators are an important class of crystal materials and widely used in the detection fields.In recent years,double tungstate systems such as NaBi?WO₄?₂,NaY?WO₄?₂,CdGd₂?WO₄?₄ have been reported gradually.There are two major groups of such materials:ARe?WO₄?₂?A is a monovalent metal ion?and ARe₂?WO₄?₄?A is a divalent metal ion?.The research mainly focused on the laser properties with rare earth ions doped,photoluminescence and crystal growth,but rarely reported on scintillation properties.In this paper,we mainly conduct the research on CdRe₂?WO₄?₄?Re=La,Gd?system and carry out the work as the following three parts:Part 1.Growth of Ce:CdGd2?WO4?4.Using CdWO4 as a seed crystal and the Ce:CdGd₂?WO₄?₄ was grown by the Czochralski method.The grown-crystal was pale yello,translucent and some cracks could be observed along the dissociation surface inside the crystal.Hereafter,crystals were processed and sliced,then measured the UV-visible transmission spectrum,photoluminescence spectrum,photoluminescence emission decay time,etc.of the crystals under the room temperature,the results were analyzed and discussed.Ce:CdGd₂?WO₄?₄ is tetragonal scheelite structure with unit cell parameters a=b=0.5188 nm and c=1.1346 nm,under the excitation of 320 nm UV light,the peak of fluorescence emission spectrum is at 525 nm and the decay time of Ce:CdGd2?WO4?4 is 1.4?s.Part 2.Investigation on high temperature solid-state reaction,crystal growth and optical properties of CdLa₂?WO₄?₄.The polycrystalline for crystal growth were synthesized at different temperatures and the optimal temperature conditions were also explored.CdLa₂?WO₄?₄ grew by spontaneous nucleation with Czochralski method and vertical Bridgman method,respectively.Additionally,X-ray powder diffraction curve,X-ray stimulated emission spectrum,UV-vis diffuse reflectance spectrum,photoluminescence decay time and other performance parameters of CdLa₂?WO₄?₄ crystal were tested.The results show that CdLa₂?WO₄?₄ belongs to tetragonal scheelite structure,fitted unit cell parameters were a=b=5.209 A?and c=11.325 A?,the unit cell volume is307.26?³ and density is 7.494 g/cm³.Moreover,with 296 nm ultraviolet light to stimulate the sample,there is a wide blue-green emission peak within the range of350-600 nm,which position is located at 470 nm,it belongs to typical tungstate luminescence peak,and photoluminescence emission decay time is 3.4 ns,it is extremely fast,CdLa₂?WO₄?₄ also show superb luminescence performance under X-ray excitation.Part 3.Growth and performance of CdGd_x La_2-x?WO₄?₄ solid solution crystals.In this thesis,a novel solid solution system CdGd_x La_2-x?WO₄?₄?x=0.2,0.4,0.6,0.8,1.0?were proposed and a series of polycrystalline materials were synthesized by high temperature solid-phase reaction,the crystal were grown by the Czochralski method.Compared with the pure CdLa₂?WO₄?₄ crystal,the CdGd_x La_2-x?WO₄?₄ is greatly improved on quality,after that,its performance were characterized and the results indicated that:with the Gd increased,luminescence intensity of the crystal get weaker under the X-ray radiation,photoluminescence luminescence also shows the same trend.Besides,the emission peaks exhibited a slight blue shift within the range of 300-600 nm and the photoluminescence emission decay time were in the range of 250-450 ns.