Study On Microstructures And Properties Of Rare-earth Doped Phosphates

Rare-earth（Re）luminescent materials are nowadays widely employed in manyquotidian devices and for this, studies on their obtainment, spectroscopic behavior andapplications have been remarkable. Among the large number of rare-earth luminescentmaterials, rare-earth doped orthophosphates and pyrophosphates are a very interestingclass of host lattices for activator ions due to their outstanding physic-chemicalproperties. Moreover, phosphate-based phosphors activated with Eu3+ions have beenpaid much attention.In this work, alkaline earth orthophosphates and pyrophosphates doped withEu2+，Eu3+,Ce3+and Tb3+ions were selected to be the host. The sample was preparedby high temperature solid-state reaction. Their structures were characterized by the X-ray powder diffraction. Their luminescent properties were studied through themeasurement of photoluminescence excitation and emission spectra, the luminescencedecay curves and the thermal stability of luminescence. By the way, Eu3+was used as aprobe corresponding to the information of site-selective excitation and emission spectrato analyze the microstructure of the materials.In chapter3, Eu2+-and Eu3+-doped MgZn2(PO4)2were prepared using the hightemperature solid-state reaction method. The excitation spectra in the UV and VUVregion, the emission spectra, and the luminescence decay curves of the Eu2+and Eu3+ions were investigated. The crystallographic distributions of the Eu2+and Eu3+sites inMgZn2(PO4)2lattices are different MgZn2(PO4)2:Eu2+presents a bluish greenluminescence with two distinct emission centers at450and520nm. MgZn2(PO4)2:Eu3+presents an reddish orange color with luminescence transitions from the5D0level of theEu3+ions. There exist two Eu2+-crystallographic sites in MgZn2(PO4)2:Eu2+, whichoccupy both Mg2+and Zn2+sites. However, there is only one Eu3+-site in theMgZn2(PO4)2:Eu3+lattices, which was confirmed by site-selective excitation andemission spectroscopy, and the luminescence decay in the5D0â†'7F0region of the Eu3+ions. The Eu3+ion was suggested to occupy the octahedral Mg2+-site in theMgZn2(PO4)2:Eu3+lattices. The temperature dependent luminescence intensity and activation energies of thermal stabilities were discussed on the basis of the crystalstructure and the luminescence results.In chapter4, Ce3+and Tb3+single doped and co-doped MgZn2(PO4)2wereprepared using the high temperature solid-state reaction method. Their structures werecharacterized by the X-ray powder diffraction. And their microtopographies werechaercterized by SEM. The excitation and emission spectra of the Ce3+and Tb3+wereinvestigated. MgZn2(PO4)2:Ce3+presents a long-wavelength ultraviolet light.ForMgZn2(PO4)2:Tb3+, the spectral-energy distribution of the Tb3+emission depends on theTb3+concentration. As to the low Tb3+concentrations, the emission spectrum consistsof the transition from both the5D3and the5D4levels. As to the high Tb3+concentrations,the transitions from the5D3â†'7FJare quenched by the cross-relaxation process betweenneighboring Tb3+ions. It was also discussing the energy transfer mechanism betweenCe3+and Tb3+on Ce3+and Tb3+co-doped MgZn2(PO4)2samples.In chapter5, Eu3+-doped SrZnP2O7were prepared by high temperature solid-statereaction method. The site-selective excitation and emission spectroscopy, and theluminescence decay have been investigated in the5D07F0region of Eu3+ions under apulsed, tunable, narrowband dye laser at300K and15K. The luminescence onlyarises from the5D0level of Eu3+ions. This study is to investigate the crystallographicdistribution of Eu3+sites in SrZnP2O7lattices, which could exhibit differentspectroscopic features. Non site-selective emission spectra under UV excitation werealso measured. There exist two Eu3+crystallography sites in SrZnP2O7, which occupyboth Sr2+and Zn2+sites in the lattices. Among the two Eu3+sites the energy transferscould be detected from the Eu3+ions on Zn2+sites to those on Sr2+sites. The possibledefects and the charge compensation mechanisms were discussed. It has proposed twohypothesis. Firstly, Eu3+ions substitute for Mg2+site and combine with Mg or Znvacancy:2Mg2+â†'2Eu3++V(Sr or Zn)″to form the dipole complexes of [2(Eu3+Mg)-V(Sr or Zn)″]. Secondly, the interstitial oxygen Oi″is possible:2Mg2+â†'2Eu3++Oi″. Thismechanism could form the dipole complexes of [2(Eu3+Mg)-Oi″].The novelties of this dissertation are as follows: the luminescence properties,microstructures and potential applications of Eu (Eu2+,Eu3+) doped orthophosphates andpyrophosphates were systematically studied. It was firstly through the site-selectiveexcitation and emission to investigate the crystallographic distributions of the Eu3+sitesin the matrix. In summary, it provides a useful reference for further development andapplication of Rare-earth luminescent materials.