Preparation,Composition,Structure And Photoluminescence Of Cerium-Containing Silicon Oxynitride Phosphors By Polymer-Derived Method

Cerium(Ce)-activated silicon oxynitride phosphors have excellent thermochemical stabilities and good luminescent properties,which are a kind of promising luminescent materials.Ce-activated metal-containing silicon oxynitride phosphors,including those containing alkaline earth metals or other metal elements such as aluminum(Al)and yttrium(Y),have been extensively studied.However,the metal-free Ce-containing silicon oxynitride phosphors have been less studied.At present,there is no relevant research on Ce-containing silicon oxynitride phosphor prepared by polymer-derived method.Therefore,it is very meaningful to explore the effects of chemical compositions,phase compositions and crystal structures on the luminescent properties of Ce-containing polymer-derived silicon oxynitride phosphors.In this work,The organic precursors were prepared via polymer reactions using polycarbonsilane(PCS)and cerium acetylacetone hydrate(Ce(AcAc)3·nH2O)as raw materials,and then undergone the nitridation and crystallization to yield the Ce-containing silicon oxynitride phosphors.By elemental analysis,X-ray diffraction(XRD),scanning electron microscopy(SEM)and photoluminescence spectroscopy,the effects of initial atomic ratio of Si:Ce and sintering processes on the chemical compositions?crystal structures and luminescent properties of the Ce-containing silicon oxynitride phosphors were systematically investigated.Moreover,the effects of magnesium(Mg)introduction on the Ce-containing phosphors were also preliminarily studied.The microstructures and the surface chemical states of the Mg-free and Mg-doped Ce-containing phosphors with the best luminescent property were analyzed by Rietveld refinement,transmission electron microscope(TEM),Raman spectroscopy and X-ray photoelectron spectroscope(XPS)techniques.It turned out that the initial atomic ratio of Si:Ce and sintering processes had little effects on the luminescent wavelengths of Ce-containing polymer-derived silicon oxynitride phosphors,all of which exhibited ultraviolet excitations in the wavelength range from 225 to 400 nm and blue emissions in the wavelength range from 400 to 500 nm.The two-step route could reduce the carbon content,improve the phase purity and luminescent intensity of the Ce-containing polymer-derived phosphor.Sintering temperature and initial atomic ratio of Si:Ce affected the crystal structures of the phosphors.When sintering temperature was less than 1600 ?,the main phases of the phosphors were ?-Si3N4 and ?-Si3N4.When sintering temperature was in the range of 1600-1650 ?,CeSi3N5 phase was appeared in the phosphors.When Ce content was increased,the contents of CeSi3N5 and CeSiO2N phases in the phosphors sintered at 1650 ? were also increased.When the initial atomic ratios of Si:Ce and(Si+Mg):Ce were 40:0.5 and(39.5+0.5):0.5,the best luminescent properties of two Ce-containing phosphors with/without Mg ions were achieved,respectively.The results indicated that both the Mg-free and Mg-doped Ce-containing phosphors with the best luminescent property exhibited a blue emission at 445 nm under the excitation at 355 nm.Mg additive could reduce the content of carbon,increase the ratio of Ce3+ and enhance the luminescent intensity of the phosphor.The major crystalline phase ?-Si3N4:Ce appeared in two space groups P63 and P63/m,leading Ce ions in the six-ring interstitial channel to be either six or nine coordinated by N/O atoms.Mg ions were located in the four-ring interstitial channel of the ?-Si3N4 and CeSi3N5 lattices coordinated by six and seven N/O atoms,respectively.