Growth And Doping Modification Of A Novel High Temperature Scintillation Crystal Mg₄Ta₂O₉

Scintillators convert the energy of the incident particle or high-energy photon into a photon of lower energy in the visible or near-visible range that make them crucial components in the application of high-energy rays.Here,we firstly doped Mg₄Ta₂O₉（MTO）with transition metal elements,which greatly shortened the decay time.Then,the combined doping of Zn²⁺and Gd³⁺were attempted,which improved the luminescence properties of MTO.Finally,MTO and Mg₄(Ta_0.6Nb_0.4)₂O₉（MTO:Nb）crystals were grown by optical floating zone method,and their structures and luminescence properties were characterized.The main results of this paper are as follows:（1）Mg₄Ta₂O₉:x at%M(M=Hf⁴⁺,Zr⁴⁺,W⁶⁺,Mo⁶⁺;x=0,1,2,3,4,5)with single phase were synthesized via the conventional solid-state reactions in air.The samples were characterized by X-ray diffraction（XRD）,room-temperature vacuum ultraviolet（VUV）light excited spectra and X-rays excited luminescence（XEL）.Structural characterization and Rietveld refinement showed that more than 60%of 5 at%Hf⁴⁺,Zr⁴⁺,W⁶⁺and Mo⁶⁺doped ions enter into the Ta sites and less than 40%ions into the Mg（1）and Mg（2）sites.They can be excited efficiently by VUV light at 160 nm,and emit wide UV-A or blue light at 355～458 nm depending on the doping ion and its concentration.XEL spectra and decay time data indicated that MTO:1 at%Hf⁴⁺has excellent X-ray excited scintillation performance typically with light yield 13469 ph/Me V and decay time of 5.28μs.Thus,it had potential application in optical conversion devices and security inspection.（2）(Mg_0.8-xZn_0.2Gd_x)₄Ta₂O₉（x=0,0.001,0.0025,0.005,0.0075,0.01）with single phase were synthesized via the conventional solid-state reactions in air.The samples were characterized by XRD,VUV luminescence properties,fluorescence decay time and XEL.Structural characterization showed that Zn²⁺and Gd³⁺can be doped into the lattice to replace Mg sites.The results of VUV spectra showed that the performance of the MTO doped with Zn²⁺and Gd³⁺were better than that of the standard sample and that of the MTO doped with Zn alone.Among them,the excitation and emission intensity of sample(Mg_0.7975Zn_0.2Gd_0.0025)₄Ta₂O₉reached the maximum value,and the emission intensity was about 3.5 times of that of MTO.The results of XEL spectra showed that the doped samples significantly improved the luminescence intensity compared with MTO,among which(Mg_0.795Zn_0.2Gd_0.005)₄Ta₂O₉ had the strongest enhancement performance,which was 2.3 times that of MTO,and the luminescence intensity was estimated to be about 36800 ph/Me V.The decay time of Zn²⁺and Gd³⁺co-doped MTO were slightly longer than that of standard sample MTO,which may be due to the distortion of the face-shared octahedron（Ta O₆）^7-by doping,which reduced the symmetry of the structure and extended the relaxation time of valence transitions around Ta⁵⁺.Therefore,sample(Mg_0.7975Zn_0.2Gd_0.0025)₄Ta₂O₉ and sample(Mg_0.795Zn_0.2Gd_0.005)₄Ta₂O₉ had the best comprehensive performance and were most likely to be used in optical conversion devices and safety detection.（3）MTO and MTO:Nb single crystals were growth by the floating zone method.The results showed that Nb⁵⁺can be successfully mixed into the lattice to replace Ta site.The photoluminescence of Nb⁵⁺doped MTO single crystal was superior to MTO,and its emission intensity was 4.4 times that of MTO,and its excitation intensity was 3.7 times that of MTO.With the introduction of Nb⁵⁺,the emission peak was redshifted from 333 nm to 376 nm.The result of XEL showed that the doped sample improved the luminescence intensity by 1.1 times of MTO,and the estimated photoluminescence yield was about 17600 ph/Me V.The phenomenon of emission peak redshift was similar to PL spectrum.The luminescence band and intensity were well adjusted,which can be applied to the wavelength sensitivity of general photodetectors.