Luminescence Characteristics Of Eu²⁺、Eu³⁺and Mn²⁺ Doped Na₂CaMg（PO₄）₂

Rare-earth （RE） doped materials have been widely applied in luminescence anddisplay, bio-medicine, laser devicesand many other fields. The luminescence ofRE-doped phosphates usually has a high thermal stability of luminescence due to therigid network of PO4tetrahedrons. So much attention is focused on this kind ofphosphors.As a member of orthophosphates, Na₂CaMg（PO₄）₂was selected to be the hostmaterial. The luminescence powder of Eu²⁺, Eu³⁺and Mn²⁺-doped Na₂CaMg（PO₄）₂wasprepared by the high temperature solid-state reaction. Their structures werecharacterized, and the excitation spectra, emission spectra, luminescence decay curves,the temperature stability of luminescence and their potential applications were alsosystematically investigated.In the chapter three, blue-emitting phosphors of Eu²⁺-doped Na₂CaMg（PO₄）₂wereprepared by high temperature solid-state reaction. The samples were characterized byscanning electron microscopy （SEM）, X-ray diffraction （XRD）, photoluminescence （PL）and fluorescence lifetime measurement. The results indicated that Na₂CaMg（PO₄）₂wasa phosphate analog of merwinite Ca3Mg（SiO4）2with space group P21/c and Z=4. Thephosphor can be excited efficiently by near UV light and emits blue light. Eu²⁺ionshave two emission centers in this phosphor that were investigated by the luminescencespectra. Na₂CaMg（PO₄）₂:Eu²⁺phosphor also showed high quenching temperature andstable color purity with the elevated temperature. The emission decreased slowly withincreasing temperature to150°C （decreases by about8%of the initial value at10k）.These results indicated that Na₂CaMg（PO₄）₂:Eu²⁺phosphors have a good thermalstability for its potential application.In the chapter four, the local structure and luminescent properties of Eu³⁺ionsdoped in Na₂CaMg（PO₄）₂were discussed on the base of the spectroscopic probe of Eu³⁺by the site-selective excitation and emission spectroscopy. The emission and excitation spectra indicate that the excitation spectrum of samples presents wide band absorptionbetween220-300nm, which is ascribed to the charge transfer between Eu³⁺-O^2-. Thesharp peaks after300nm belong to f-f transition of Eu³⁺, and the strongest sharp peak islocated at393nm. The emission spectrum consists of two strong emission peaks at585nm、592nm and610nm、618nm, which are ascribed to⁵D₀�'⁷F₁and⁵D₀�'⁷F₂respectively. Moreover, the Eu³⁺doping effect on luminescent properties was discussed.In the chapter five, Mn²⁺-doped phosphates Na₂CaMg_1-xMn_x（PO₄）₂（x=0.05-1.0）were prepared by the same method. The XRD patterns show that the samples withx=0.05-0.3maintain the single low-temperature monoclinic α-phase. For x-valuebetween0.3and0.6, the samples contain two distinct phases, α-and β-phase. Thecompounds of Na₂CaMg_1-xMn_x（PO₄）₂（0.65≤x≤1.0） present only a single β-phase.The shrinkage of the lattice volume takes place due to the Mn²⁺doping. The emissionwavelength of Na₂CaMg_1-xMn_x（PO₄）₂（x=0.05-1.0） shifts to longer wavelength whenincreasing Mn²⁺-concentration. The lifetime values of the emission from Mn²⁺ionsdecrease from21to7.5ms as the Mn²⁺-concentration increases from x=0.05to1.0. Asthe Mn²⁺doping increases, the CIE coordinates （x, y） vary systematically from orangered （0.6,0.4）（x=0.05） to a deep-red color （0.68,0.3）（x=1.0）. The results are discussedin relation with the detailed crystal structure and the spectral analyses. The difference ofemission color can be attributed to the difference of chemical environment around Mn²⁺.The CIE coordinates and the luminescence decay （lifetimes） of Mn²⁺ions werediscussed in order to further investigate the potential applications.In the chapter six, the spectroscopic properties of the Ce³⁺ions were investigatedby vacuum ultraviolet spectroscopy. The energy transfer from the host to Ce³⁺ions wasdemonstrated. The phosphor could be excited by VUV light and showed a broadpurplish blue emission with the maximum wavelength at385nm. Under the excitationat147nm, the Na₂CaMg（PO₄）₂:Ce³⁺shows a typical doublet character on the emissionband due to the spin–orbit splitting of ground state （2F5/2and2F7/2）. The spectroscopicparameters, e.g., the barycenter, host absorption bands, crystal field splitting and stokesshift were discussed.The novelties of this dissertation are as follows: the structure characteristics,photoluminescence performances and luminescence decays of Eu²⁺、Eu³⁺and Mn²⁺doped Na₂CaMg（PO₄）₂were systematically studied. The features about microstructure of Na₂CaMg（PO₄）₂were firstly investigated by the site-selective excitation and emissionspectra. The spectroscopic parameters of Ce³⁺ion doped Na₂CaMg（PO₄）₂phosphor andthe phase formations and luminescence characteristics of Na₂CaMg_1-xMn_x（PO₄）₂（x=0.05¹.0） were firstly investigated. Overall, it provided a useful reference for furtherdevelopment and application of RE-doped Na₂CaMg（PO₄）₂phosphor.