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
Low-lying electronic states of the lutetium dimer （Lu2） were studied based on density functional theory （DFT） using ten different density functionals together with three different relativistic effective core pseud...Low-lying electronic states of the lutetium dimer （Lu2） were studied based on density functional theory （DFT） using ten different density functionals together with three different relativistic effective core pseudopotentials （RECPs）. Relative state energies, equilibrium bond lengths, vibrational frequencies, and ground-state dissociation energies were evaluated. It was found that the ground state is a triplet state irrespective of the type of functional and RECP used. This result is in contrast with a previous DFT calculation which gave a singlet ground state for Lu2. By comparing with the high-level ab initio and available experimental results, it is evident that the hybrid-GGA functionals combined with the Stuttgart smallcore RECP yield the best overall agreement for the properties under study. The effects of Hartree-Fock exchange in B3LYP functional on the calculated bond length and dissociation energy of the ground state were examined, and rationalized in terms of 5d participation in Lu-Lu covalent bonding.展开更多
Density functional theory calculations were performed to study the structures and relative stability of the gadolinium complexes, Gd（H2O）n^3＋ （n=8,9）, in vacuo and in aqueous solution. The polarizable continuum m...Density functional theory calculations were performed to study the structures and relative stability of the gadolinium complexes, Gd（H2O）n^3＋ （n=8,9）, in vacuo and in aqueous solution. The polarizable continuum model with various radii for the solute cavity was used to study the relative stability in aqueous solution. The calculated molecular geometries for n=8 and 9 obtained in vacuo are consistent with those observed in experiments. It was found that while the nona-aqua complex is favored in the gas phase, in aqueous solution the octa-aqua conformation is preferred. This result, independent of the types of cavities employed, is in agreement with the experimental observation. The reliability of the present calculation was also addressed by comparing the calculated and experimental free energy of hydration, which revealed that the UA0, UAHF, and UAKS cavities are most appropriate when only the first solvation shell is treated explicitly.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
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
Optical absorption spectra of Sm(DBM) 3 doped PMMA (polymethyl methacrylate) in near infrared and visible region are presented. The energy levels were assigned and analyzed in terms of the free-ion Hamiltonian model....Optical absorption spectra of Sm(DBM) 3 doped PMMA (polymethyl methacrylate) in near infrared and visible region are presented. The energy levels were assigned and analyzed in terms of the free-ion Hamiltonian model. Energy levels and reduced matrix elements calculations were carried out using the complete 198 SLJ basis sets for the 4f5 configuration. Judd-Ofelt parameters were evaluated and used to predict the radiative properties of the sample. The theoretical and experimental values for radiative lifetimes and branching ratios were discussed.展开更多
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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.10804001, No.10674002, and No.20773024）, the National High Technology Research and Development Program of China （863 Program） （No.2006AA09Z243-3）, and the Program for Innovative Research Team in Anhui Normal University of China.
文摘Low-lying electronic states of the lutetium dimer （Lu2） were studied based on density functional theory （DFT） using ten different density functionals together with three different relativistic effective core pseudopotentials （RECPs）. Relative state energies, equilibrium bond lengths, vibrational frequencies, and ground-state dissociation energies were evaluated. It was found that the ground state is a triplet state irrespective of the type of functional and RECP used. This result is in contrast with a previous DFT calculation which gave a singlet ground state for Lu2. By comparing with the high-level ab initio and available experimental results, it is evident that the hybrid-GGA functionals combined with the Stuttgart smallcore RECP yield the best overall agreement for the properties under study. The effects of Hartree-Fock exchange in B3LYP functional on the calculated bond length and dissociation energy of the ground state were examined, and rationalized in terms of 5d participation in Lu-Lu covalent bonding.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.10804001, No.10674002, and No.20773024）, the National High Technology Research and Development Program of China （No.2006AA09Z243-3）, and the Program for Innovative Research Team in Anhui Normal University of China.
文摘Density functional theory calculations were performed to study the structures and relative stability of the gadolinium complexes, Gd（H2O）n^3＋ （n=8,9）, in vacuo and in aqueous solution. The polarizable continuum model with various radii for the solute cavity was used to study the relative stability in aqueous solution. The calculated molecular geometries for n=8 and 9 obtained in vacuo are consistent with those observed in experiments. It was found that while the nona-aqua complex is favored in the gas phase, in aqueous solution the octa-aqua conformation is preferred. This result, independent of the types of cavities employed, is in agreement with the experimental observation. The reliability of the present calculation was also addressed by comparing the calculated and experimental free energy of hydration, which revealed that the UA0, UAHF, and UAKS cavities are most appropriate when only the first solvation shell is treated explicitly.
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.
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Optical absorption spectra of Sm(DBM) 3 doped PMMA (polymethyl methacrylate) in near infrared and visible region are presented. The energy levels were assigned and analyzed in terms of the free-ion Hamiltonian model. Energy levels and reduced matrix elements calculations were carried out using the complete 198 SLJ basis sets for the 4f5 configuration. Judd-Ofelt parameters were evaluated and used to predict the radiative properties of the sample. The theoretical and experimental values for radiative lifetimes and branching ratios were discussed.
