DOE OSTI2015
The relationship between the photoluminescence properties and the crystal structure of undoped, Eu{sup 3+} or/ and Tm{sup 3+} singly or codoped Ca{sub 9}La(VO{sub 4}){sub 7} (CLaVO) samples was discussed. Under the excitation of UV light, CLaVO:Tm{sup 3+}, CLaVO, and CLaVO:Eu{sup 3+} exhibit the characteristic emissions of Tm{sup 3+} ({sup 1}G{sub 4}→{sup 3}H{sub 6}, blue), O{sup 2−}→V{sup 5+} charge transfer (CT), and Eu{sup 3+} ({sup 5}D{sub 0}→{sup 7}F{sub 2}, red), respectively. By adjusting the doping concentration of Tm{sup 3+} and Eu{sup 3+} ions in CLaVO, a natural white emission in a single composition with the color temperature at 6181 K was obtained. Based on the dielectric theory of complex crystal, the chemical bond parameters of La-O and V-O bonds were quantitatively calculated. The standard deviation of environmental factor of every bond (EFSD), which can be expressed as σ(h{sub e{sub i}})=√((1/N)∑{sub i=1}{sup N}(h{sub e{sub i}}−μ){sup 2}) (h{sub e{sub i}}=(f{sub c{sub i}}α{sub b{sub i}}){sup 1/2}Q{sub B{sub i}} and μ=(1/N)∑{sub i=1}{sup N}h{sub e{sub i}}), was proposed to quantitatively express the distortion degree of VO{sub 4}{sup 3−} from that of an ideal tetrahedron. The maximum change of EFSD comes from the [VO{sub 4}]{sup −} tetrahedra in CLaVO sample by comparison with that of EFSD of isostructural Ca{sub 9}Gd(VO{sub 4}){sub 7}. This is possible the key reason that the undoped CLaVO sample has self-activated emission while the self-activated emission of its isostructural Ca{sub 9}Gd(VO{sub 4}){sub 7} sample cannot be found. The quantitative calculation also demonstrated that the broad excitation bands at 319 nm in CLaVO:Tm and at 335 nm in CLaVO:Eu were due to the O-V2 and O-V3 (overlap with O-V2) CT, not the CT energy of O{sup 2−}-Eu1{sup 3+} (O{sup 2−}-Tm1{sup 3+}), O{sup 2−}-Eu2{sup 3+} (O{sup 2−}-Tm2{sup 3+}), and O{sup 2−}-Eu3{sup 3+} (O{sup 2−}-Tm3{sup 3+}). The environmental factors surrounding the atoms V1, V2 and V3 were calculated to be 1.577, 1.6379 and 1.7554, respectively. It can be demonstrated that the excitation spectra at 319 nm for CLaVO:Tm and 335 nm for CLaVO:Eu came from the O-V2 and O-V3 CT, respectively. - Graphical abstracts: The relationship between the photoluminescence properties and the crystal structure of undoped, Eu{sup 3+} or/ and Tm{sup 3+} singly or codoped Ca{sub 9}La(VO{sub 4}){sub 7} (CLaVO) samples was discussed experimentally and theoretically. - Highlights: ●The photoluminescence properties of Ca{sub 9}La(VO{sub 4}){sub 7}:Eu, Tm were measured. ●The tunable color including white emission can be obtained. ●The important chemical bond parameters of O-V were calculated quantitatively. ●The standard deviation of environmental factor of every bond was proposed. ●The theoretical analysis of the self-activated emission for Ca{sub 9}La(VO{sub 4}){sub 7} was given.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗