Luminescence And Microstructure Properties Of Rare Earth Eu₃₊ Ions

Rare earth（RE） occupies almost the entire field of solid luminescence due to its unique chemical and physical properties. All luminescence materials are related to rare earth, which ha been used in machinery, glass, ceramics, lighting, electronics, aerospace, biomedical and other fields. Eu is one of most studied RE elements and Eu³⁺ ion is the typical red emission ion. The emission spectra of Eu³⁺ ion are from the transition of 4f-4f and are closely related to the structure of the matrix. When Eu³⁺ ion is located at the site with no inversion symmetry in all the lattices, the dominated emission transitions are hypersensitive forced electric dipole transition（⁵D0â†'⁷F2）. On the contrary, the magnetic dipole transitions（⁵D0â†'⁷F1） are dominated. Also, the number of split peaks of ⁵D0â†'⁷F0 transition is the the number of crystallography sites of Eu³⁺ in the lattices. The good luminescent properties and the probe characteristic determine the important position of Eu³⁺ ions in the various fields.In this work, the borate, niobate, and molybdate were selected as host and the Eu³⁺ doped phosphors were prepared by high temperature solid state reaction. X-ray powder diffraction analysis（XRD）, Scanning electron microscope（SEM）, X-ray energy-dispersive spectra（EDS）, Raman spectra, Excitation and emission spectra, and Luminescence decay were measured for studying the microstructure and luminescence of Eu³⁺ ion and analyzing its potential applications in different fields.In chapter 3, CaB₂O₄:Eu³⁺ powder and ceramics were prepared by the conventional solid-state reaction. XRD, SEM, and EDS measurements were applied to investigate the structure, surface morphology, and the elemental compositions on the surface of the soaked samples. Combining with the probe property of Eu³⁺ ion, the luminescence evolution and potential applications of samples were studied by photoluminescence spectra and photoluminescence decay curves. The results suggested the characteristic peaks of CaB₂O₄ decreased and new peaks corresponding to the reflection of HA could be observed with the mineralization time increasing. HA can form flower-like nanostructures, which confirms the samples possess the ability of forming the HA when soaked in SBF solutions. Also, the luminescence spectra show regular changes. The intensity ratio between the luminescence transitions（⁵D0â†'⁷F2） and（⁵D0â†'⁷F1） is close to 1 gradually. ⁵D0â†'⁷F4 transition presented unusual intensity, and Eu²⁺ ions could be detected at the final stage of mineralization. This suggested that the phase transformation process of HA mineralization can be monitored by the luminescence of Eu³⁺ ions due to its probe characteristic.In chapter 4, Eu³⁺-doped La₃Mg₂NbO₉ red-emitting ceramics were prepared via typical solid state. X-ray diffraction and scanning electron microscope were utilized to characterize the ceramics. The results confirm the ceramics adopt perovskite-type structure. There are no impurity peaks if the doping level is less than 10 mol%. The average size of particles is 300-500 nm. As a structure probe, the photoluminescence excitation and emission spectra, and the fluorescence decay curves were investigated to confirm the crystallography sites of Eu³⁺ ions in the lattices and the structure of the host. Upon the excitation of blue irradiation at 460 nm, the highest emission intensity observed for the samples is the hypersensitive forced electric dipole transition（⁵D0â†'⁷F2） at 615 nm of Eu³⁺. This indicates that Eu³⁺ ion is located at the site with no inversion symmetry in the lattice. Also, raman spectra was used to further determine the microstructure of Eu³⁺ ion in the lattice. The CIE chromaticity coordinates was calculated to be（0.665, 0.341）. This suggested that Eu³⁺ ions only substitute La³⁺ sites without inversion symmetry and the crystal structure of La₃Mg₂NbO₉ is heavily distorted due to the mixed occupation of Mg and Nb.In chapter 5, Eu³⁺-doped NaLa₄Mo₃O₁₅ F was prepared by solid-state method and characterized by X-ray powder diffraction and scanning electron microscope. No impurity peaks were found. The luminescence properties were investigated, such as the excitation spectra and emission spectra. The optimal level of Eu³⁺-doping was 70 mol%. The phosphor exhibits a bright red luminescence at 615 nm corresponding to the electric dipole transition ⁵D0â†'⁷F2 under the excitation of near UV or blue light. With the increase of Eu³⁺-doping the charge transfer band（CTB） shows an obvious red-shift, which presents a longer wavelength than any other reported Eu³⁺-doped molydates with non-cubic structures. This is benefited from its structural characteristics: the cubic crystalline phase with MoO₆ groups and the incorporation of F- ions in the host lattices. Then the QEs and CIE were measured. Combined with the thermal stability measurement, the obtained results have demonstrated the potentiality of NaLa₄[Mo₃O₁₅]F:Eu³⁺ for nearUV/blue GaN-based white LEDs.This work has systematically studied the luminescence and microstructure properties of Eu³⁺ ions doped borate, niobate, and molybdate. The application of structure probe of Eu³⁺ ion in biomaterial CaB₂O₄ was firstly studied to open the potential significance for biomineralization in the field of biological monitoring. Then, the typical luminescence and microstructure properties of Eu³⁺ ion doped La₃Mg₂NbO₉ was investigated. With the increase of Eu³⁺-doping the charge transfer band（CTB） shows an obvious red-shift in the excitation spectra of NaLa₄Mo₃O₁₅F:Eu³⁺. The results suggested the phosphors possess important reference value for further development and application of rare earth luminescent materials.