Two 3d-4f-5d heterometallic cluster-containing polyoxometalates,formulated as Na_(22){(SbW_(9)O_(33))_(4)[La_(3)W_(6)MO_(18)(H_(2)O)_(8)(CH_(3)COO)_(4)]_(2)}·nH_(2)O(abbreviated as La_(6)M_(2),M=Co/Mn)were synthe...Two 3d-4f-5d heterometallic cluster-containing polyoxometalates,formulated as Na_(22){(SbW_(9)O_(33))_(4)[La_(3)W_(6)MO_(18)(H_(2)O)_(8)(CH_(3)COO)_(4)]_(2)}·nH_(2)O(abbreviated as La_(6)M_(2),M=Co/Mn)were synthesized and structurally characterized.Single-crystal X-ray diffraction analyses reveal that the polyanions of La_(6)Co_(2)and La_(6)Mn_(2)consist of the uncommon 3d-4f-5d clusters{La_(6)W_(12)Co_(2)}and{La_(6)W_(12)Mn_(2)},which are encapsulated by four trilacunary Keggin tungstoantimonates to form the parallelogram-shaped title compounds.Additionally,the polyanions can be extended into a two-dimensional(2D)frame by the linkage of peripheral Na+ions.The inner space of the 2D layer was filled with water molecules and thus an H-bonded network was formed,which is expected to exhibit a fascinating proton conductivity.The study of water-assisted proton conduction demonstrated that La_(6)Co_(2)and La_(6)Mn_(2)were temperature-and humiditydependent proton conductors,respectively,and the proton conductivities could reach 1.3×10^(-2)and 2.3×10^(-2)S/cm at 65℃and 90%RH conditions.展开更多
We have investigated properties of the compound LuAlO3：Ce^3＋ associated with the Ce^3＋ 4f-5d transition by using the periodic density functional theory. A hybrid functional has been used for the 4f states and a con...We have investigated properties of the compound LuAlO3：Ce^3＋ associated with the Ce^3＋ 4f-5d transition by using the periodic density functional theory. A hybrid functional has been used for the 4f states and a constrained approach has been employed for the excited 5d state. It is found that the average distance between Ce^3＋ and the eight nearest-neighbor O atoms decrease by 0.05 A on going from 4f to 5d state. The calculated Stokes shift is in good agreement with experiment. Based on the optimized structure around Ce^3＋, the energy level scheme of the 5d states has been evaluated using the angular overlap model, in reasonable agreement with experiment.展开更多
The electronic structures of LiYF4：Ce^3＋ and LiYF4 crystal simulated by an embedded （in a microcrystal containing 1938 ions） cluster CeY4Li8F24, and Y5LisF24 respectively, were computed by the ab initio self-consi...The electronic structures of LiYF4：Ce^3＋ and LiYF4 crystal simulated by an embedded （in a microcrystal containing 1938 ions） cluster CeY4Li8F24, and Y5LisF24 respectively, were computed by the ab initio self-consistent relativistic DV-Xa （discrete variational Xa） method. The ground-state calculation showed that only the lowest 5d level Ed of Ce^3＋ ion lies around the BCB （bottom of the conduction band） while the lowest 4f levels is 2.5 eV lower than BCB. The CB states consist of 4d of Y mixed with 5d of Ce, even for the wavefunctions （WFS） with energy Ed under BCB there are still 24% of Y-4d and 9% of F-2p as components. So, they are not pure crystal-field states at all. Furthermore, transition state （TS） calculation was performed to obtain the 4f→5d transition energies Efd, to improve the previous calculation performed by Andriessen et al, in which a small CeF8 cluster embedded in an array of point charge was used and the results of ground-state calculation were roughly used to compare with the observed 4f→5 d transition energies. The ionic radius of Ce^3＋ is larger than that of y^3＋ , so we had also modeled approximately the lattice relaxation. As results, the CeY4Li8F24 cluster with 4.56 % outward relaxation （of the nearest-neighbor and next nearest-neighbor eight fluorines） has the lowest total energy and gave satisfactory 4f→5d energies Efd, but the ground-state calculated Ed is 0.68 eV higher than BCB. For another cluster with 7.36% outward relaxation the Ed is 0.43 eV lower than BCB, which makes the observation of fine structure （including zero-phonon line） of the lowest 5 d band understandable easier, but the splits between the transition energies Efd were not as good as the former. Therefore, we consider the relaxation is some how around 4. 56% -7.36% outward, not as large as 10% proposed by Andriessen et al.展开更多
The electronic structures of LiYF4：Ce^3＋ and LiYF4 crystal simulated by an embedded （in a microcrystal containing 1938 ions） cluster CeY4Li8F24, and Y5LisF24 respectively, were computed by the ab initio self-consi...The electronic structures of LiYF4：Ce^3＋ and LiYF4 crystal simulated by an embedded （in a microcrystal containing 1938 ions） cluster CeY4Li8F24, and Y5LisF24 respectively, were computed by the ab initio self-consistent relativistic DV-Xa （discrete variational Xa） method. The ground-state calculation showed that only the lowest 5d level Ed of Ce^3＋ ion lies around the BCB （bottom of the conduction band） while the lowest 4f levels is 2.5 eV lower than BCB. The CB states consist of 4d of Y mixed with 5d of Ce, even for the wavefunctions （WFS） with energy Ed under BCB there are still 24% of Y-4d and 9% of F-2p as components. So, they are not pure crystal-field states at all. Furthermore, transition state （TS） calculation was performed to obtain the 4f→5d transition energies Efd, to improve the previous calculation performed by Andriessen et al, in which a small CeF8 cluster embedded in an array of point charge was used and the results of ground-state calculation were roughly used to compare with the observed 4f→5 d transition energies. The ionic radius of Ce^3＋ is larger than that of y^3＋ , so we had also modeled approximately the lattice relaxation. As results, the CeY4Li8F24 cluster with 4.56 % outward relaxation （of the nearest-neighbor and next nearest-neighbor eight fluorines） has the lowest total energy and gave satisfactory 4f→5d energies Efd, but the ground-state calculated Ed is 0.68 eV higher than BCB. For another cluster with 7.36% outward relaxation the Ed is 0.43 eV lower than BCB, which makes the observation of fine structure （including zero-phonon line） of the lowest 5 d band understandable easier, but the splits between the transition energies Efd were not as good as the former. Therefore, we consider the relaxation is some how around 4. 56% -7.36% outward, not as large as 10% proposed by Andriessen et al.展开更多
(GdCa)(SiO)Oapatite crystals doped with different concentrations of Ce were synthesized by the Floating Zone(FZ) method, and we have evaluated the photoluminescence(PL) and radio luminescence(RL) properties. In PL, an...(GdCa)(SiO)Oapatite crystals doped with different concentrations of Ce were synthesized by the Floating Zone(FZ) method, and we have evaluated the photoluminescence(PL) and radio luminescence(RL) properties. In PL, an emission band appeared around 400 nm under excitation at 300 nm due to the5 d-4 f transitions of Ce3+. The PL decay curves were approximated by a second-order exponential decay function, and the derived decay time constants ranged around 20-25 ns and 40-480 ns. Similar emission was observed in RL, but the decay time constants were much longer than those in PL. The RL afterglow was the lowest in the 1.0% Ce-doped sample. The 1.0% and 2.0% Ce-doped samples showed a full-energy peak in the pulse height spectrum measured underAm 5.5 MeV α-ray irradiation, and the absolute scintillation light yields were estimated to be around 55 and 36 ph/5.5 MeV-a, respectively.展开更多
We report an ab initio〉/I〉 study of spectral properties of Ce^3＋ doped at Na＋ site of the NaF crys-tal, with the charge imbalance compensated by two oxygen substitutions for fluoride （OF＇） in the first coordina...We report an ab initio〉/I〉 study of spectral properties of Ce^3＋ doped at Na＋ site of the NaF crys-tal, with the charge imbalance compensated by two oxygen substitutions for fluoride （OF＇） in the first coordination shell or two sodium vacancies （VNa＇） in the second coordination sphere. Density functional theory calculations within the supercell model are first performed to op-timize the local structures of the charge-compensated Ce^3＋, based on which Ce-centered embedded clusters are constructed and wave function-based CASSCF/CASPT2/RASSI-SO calculations are carried out to obtain the energies of 4f1 and 5d1 levels. By comparing the calculated 4f→5d transition energies with experimental excitation spectra at low temper-atures, the lowest 4f→5d transition band peaked at 390 nm is assigned to the Ce^3＋ with charge compensation by two coordinating OF＇ substitutions, rather than to the Ce^3＋ with compensation by two VNa0 vacancies, as proposed earlier. The electronic reason for the large redshift （by -8000 cm-1） of the lowest 4f→5d transition as induced by the two nearby OF＇ substitutions is analyzed in terms of the changes in the centroid shift and crystal-field splitting.展开更多
Charge compensation plays a very important role in modifying the local atomic structure and moreover the spectroscopic property of an isolated luminescent center, and so has been widely adopted in phosphor designs. In...Charge compensation plays a very important role in modifying the local atomic structure and moreover the spectroscopic property of an isolated luminescent center, and so has been widely adopted in phosphor designs. In this work, we carry out first-principles calculations on various cases of Ce3＋ centers in Ca3Sc2Si3O12 by considering the effects of the charge com- pensations related to N3-, Sc3＋, Mn2＋, Mg2＋, and Na＋. Firstly, the local structures around Ce3＋ are optimized by using density functional theory calculations with supercell model. The 4f→5d transition energies of Ce3＋ are then obtained from the CASSCF/CASPT2/RASSI-SO calculations performed on Ce3＋-centered embedded clusters. The calculated energies support the previous assignments of the experimental spectra. Especially, a previously unclear peak is identified to be caused by Sc3＋ substituting Si4＋. The results show that the first-principles calculations can be used as an effective tool for predicting and interpreting spectroscopic properties of the phosphors.展开更多
基金supported by the National Natural Science Foundation of China(No.22071045)the Excellent Youth Science Fund Project of Henan Province(No.202300410042)+2 种基金the Natural Science Foundation of Henan Province(No.232300420372)Henan Universitythe State Key Laboratory of Physical Chemistry of the Solid Surface of Xiamen University。
文摘Two 3d-4f-5d heterometallic cluster-containing polyoxometalates,formulated as Na_(22){(SbW_(9)O_(33))_(4)[La_(3)W_(6)MO_(18)(H_(2)O)_(8)(CH_(3)COO)_(4)]_(2)}·nH_(2)O(abbreviated as La_(6)M_(2),M=Co/Mn)were synthesized and structurally characterized.Single-crystal X-ray diffraction analyses reveal that the polyanions of La_(6)Co_(2)and La_(6)Mn_(2)consist of the uncommon 3d-4f-5d clusters{La_(6)W_(12)Co_(2)}and{La_(6)W_(12)Mn_(2)},which are encapsulated by four trilacunary Keggin tungstoantimonates to form the parallelogram-shaped title compounds.Additionally,the polyanions can be extended into a two-dimensional(2D)frame by the linkage of peripheral Na+ions.The inner space of the 2D layer was filled with water molecules and thus an H-bonded network was formed,which is expected to exhibit a fascinating proton conductivity.The study of water-assisted proton conduction demonstrated that La_(6)Co_(2)and La_(6)Mn_(2)were temperature-and humiditydependent proton conductors,respectively,and the proton conductivities could reach 1.3×10^(-2)and 2.3×10^(-2)S/cm at 65℃and 90%RH conditions.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.10804001 and No.11074003）, the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, and the program for innovative research team in Anhui Normal University of China.
文摘We have investigated properties of the compound LuAlO3：Ce^3＋ associated with the Ce^3＋ 4f-5d transition by using the periodic density functional theory. A hybrid functional has been used for the 4f states and a constrained approach has been employed for the excited 5d state. It is found that the average distance between Ce^3＋ and the eight nearest-neighbor O atoms decrease by 0.05 A on going from 4f to 5d state. The calculated Stokes shift is in good agreement with experiment. Based on the optimized structure around Ce^3＋, the energy level scheme of the 5d states has been evaluated using the angular overlap model, in reasonable agreement with experiment.
文摘The electronic structures of LiYF4：Ce^3＋ and LiYF4 crystal simulated by an embedded （in a microcrystal containing 1938 ions） cluster CeY4Li8F24, and Y5LisF24 respectively, were computed by the ab initio self-consistent relativistic DV-Xa （discrete variational Xa） method. The ground-state calculation showed that only the lowest 5d level Ed of Ce^3＋ ion lies around the BCB （bottom of the conduction band） while the lowest 4f levels is 2.5 eV lower than BCB. The CB states consist of 4d of Y mixed with 5d of Ce, even for the wavefunctions （WFS） with energy Ed under BCB there are still 24% of Y-4d and 9% of F-2p as components. So, they are not pure crystal-field states at all. Furthermore, transition state （TS） calculation was performed to obtain the 4f→5d transition energies Efd, to improve the previous calculation performed by Andriessen et al, in which a small CeF8 cluster embedded in an array of point charge was used and the results of ground-state calculation were roughly used to compare with the observed 4f→5 d transition energies. The ionic radius of Ce^3＋ is larger than that of y^3＋ , so we had also modeled approximately the lattice relaxation. As results, the CeY4Li8F24 cluster with 4.56 % outward relaxation （of the nearest-neighbor and next nearest-neighbor eight fluorines） has the lowest total energy and gave satisfactory 4f→5d energies Efd, but the ground-state calculated Ed is 0.68 eV higher than BCB. For another cluster with 7.36% outward relaxation the Ed is 0.43 eV lower than BCB, which makes the observation of fine structure （including zero-phonon line） of the lowest 5 d band understandable easier, but the splits between the transition energies Efd were not as good as the former. Therefore, we consider the relaxation is some how around 4. 56% -7.36% outward, not as large as 10% proposed by Andriessen et al.
文摘The electronic structures of LiYF4：Ce^3＋ and LiYF4 crystal simulated by an embedded （in a microcrystal containing 1938 ions） cluster CeY4Li8F24, and Y5LisF24 respectively, were computed by the ab initio self-consistent relativistic DV-Xa （discrete variational Xa） method. The ground-state calculation showed that only the lowest 5d level Ed of Ce^3＋ ion lies around the BCB （bottom of the conduction band） while the lowest 4f levels is 2.5 eV lower than BCB. The CB states consist of 4d of Y mixed with 5d of Ce, even for the wavefunctions （WFS） with energy Ed under BCB there are still 24% of Y-4d and 9% of F-2p as components. So, they are not pure crystal-field states at all. Furthermore, transition state （TS） calculation was performed to obtain the 4f→5d transition energies Efd, to improve the previous calculation performed by Andriessen et al, in which a small CeF8 cluster embedded in an array of point charge was used and the results of ground-state calculation were roughly used to compare with the observed 4f→5 d transition energies. The ionic radius of Ce^3＋ is larger than that of y^3＋ , so we had also modeled approximately the lattice relaxation. As results, the CeY4Li8F24 cluster with 4.56 % outward relaxation （of the nearest-neighbor and next nearest-neighbor eight fluorines） has the lowest total energy and gave satisfactory 4f→5d energies Efd, but the ground-state calculated Ed is 0.68 eV higher than BCB. For another cluster with 7.36% outward relaxation the Ed is 0.43 eV lower than BCB, which makes the observation of fine structure （including zero-phonon line） of the lowest 5 d band understandable easier, but the splits between the transition energies Efd were not as good as the former. Therefore, we consider the relaxation is some how around 4. 56% -7.36% outward, not as large as 10% proposed by Andriessen et al.
基金Project supported by a Grant-in-Aid for Scientific Research(A) 26249147 from the Ministry of Education,Culture,Sports,Science and Technology of Japan(MEXT)JST A-step,Cooperative Research Project of Research Institute of Electronics,Shizuoka University+1 种基金Inamori FoundationKRF Foundation
文摘(GdCa)(SiO)Oapatite crystals doped with different concentrations of Ce were synthesized by the Floating Zone(FZ) method, and we have evaluated the photoluminescence(PL) and radio luminescence(RL) properties. In PL, an emission band appeared around 400 nm under excitation at 300 nm due to the5 d-4 f transitions of Ce3+. The PL decay curves were approximated by a second-order exponential decay function, and the derived decay time constants ranged around 20-25 ns and 40-480 ns. Similar emission was observed in RL, but the decay time constants were much longer than those in PL. The RL afterglow was the lowest in the 1.0% Ce-doped sample. The 1.0% and 2.0% Ce-doped samples showed a full-energy peak in the pulse height spectrum measured underAm 5.5 MeV α-ray irradiation, and the absolute scintillation light yields were estimated to be around 55 and 36 ph/5.5 MeV-a, respectively.
文摘We report an ab initio〉/I〉 study of spectral properties of Ce^3＋ doped at Na＋ site of the NaF crys-tal, with the charge imbalance compensated by two oxygen substitutions for fluoride （OF＇） in the first coordination shell or two sodium vacancies （VNa＇） in the second coordination sphere. Density functional theory calculations within the supercell model are first performed to op-timize the local structures of the charge-compensated Ce^3＋, based on which Ce-centered embedded clusters are constructed and wave function-based CASSCF/CASPT2/RASSI-SO calculations are carried out to obtain the energies of 4f1 and 5d1 levels. By comparing the calculated 4f→5d transition energies with experimental excitation spectra at low temper-atures, the lowest 4f→5d transition band peaked at 390 nm is assigned to the Ce^3＋ with charge compensation by two coordinating OF＇ substitutions, rather than to the Ce^3＋ with compensation by two VNa0 vacancies, as proposed earlier. The electronic reason for the large redshift （by -8000 cm-1） of the lowest 4f→5d transition as induced by the two nearby OF＇ substitutions is analyzed in terms of the changes in the centroid shift and crystal-field splitting.
基金This work was supported by the National Key Basic Research Program of China （No.2013CB921800）, the National Natural Science Foundation of China （No.11374291, No.11311120047, No.11274299, No.11447197, and No.11204292）, the Fundamen- tal Research Funds for the Central Universities （No.WK20304200）, the Anhui Provincial Natural Science Foundation （No.1508085QA09）. The numerical calculations have been partially done on the super- computing system in the Supercomputing Center of University of Science and Technology of China.
文摘Charge compensation plays a very important role in modifying the local atomic structure and moreover the spectroscopic property of an isolated luminescent center, and so has been widely adopted in phosphor designs. In this work, we carry out first-principles calculations on various cases of Ce3＋ centers in Ca3Sc2Si3O12 by considering the effects of the charge com- pensations related to N3-, Sc3＋, Mn2＋, Mg2＋, and Na＋. Firstly, the local structures around Ce3＋ are optimized by using density functional theory calculations with supercell model. The 4f→5d transition energies of Ce3＋ are then obtained from the CASSCF/CASPT2/RASSI-SO calculations performed on Ce3＋-centered embedded clusters. The calculated energies support the previous assignments of the experimental spectra. Especially, a previously unclear peak is identified to be caused by Sc3＋ substituting Si4＋. The results show that the first-principles calculations can be used as an effective tool for predicting and interpreting spectroscopic properties of the phosphors.
