Synthesis And Characterization Of Red MY₂S₄(M=Ca, Sr, Ba) Micro/nano-phosphor

Rare-earth ternary sulfides with the formula MRE2S4 (M=Ca, Sr, Ba;RE=La,Y) have bandgaps in the range of 2.3-3.6 eV so that the materials appear to be suitable phosphor hosts. The luminescent properties of SrY₂S₄:Eu²⁺ phosphor very resemble that of CaS:Eu²⁺ because both have broad-band emission in red region and their excitation spectra extend from ultraviolet light to visible light (250-550 run). Besides, the excellent thermal stability, strength and infrared transmission characteristics of MRE2S4 make them good candidates to be studied for novel IR optical window materials while CaS is hydrolysis in ambient giving off H2S. Therefore, there are significance and application value for the synthesis of SrY₂S4:Eu²⁺ phosphor which can substitute for CaS:Eu²⁺ in the applications of sunlight-conversion, light emitting diode(LED), electroluminescence(EL) devices.It was reported that the solid-state reaction in H₂S atmosphere took a long calcination time (3-4 d) to prepare a homogeneous SrY₂S₄:Eu²⁺, which was out of distance from practical application of phosphor. The appropriate firing temperature for SrY₂S₄:Eu²⁺ obtained from a flux-aided solid-state reaction must be 1300 °C for 8 h too. Therefore, the optimum synthesizing technique of ternary sulfide for SrY₂S₄:Eu²⁺ phosphor must be tried to investigate because the promising synthesizing technique have at least two advantages such as lower calcination temperature and shorter heating time. Although ultrafine MRE₂S₄ materials have always been synthesized by precursors such as carbonate, alkoxide and thiolate, the nanosized MRE₂S₄ materials have not been reported up to the present. In this article, we studied the synthesis of micro-/nano-meter SrY₂S₄:Eu²⁺ phosphor on the basis of synthesizing methods, at the same time,the luminescent properties of Er3+ in SrY2S4 host were observed.1. Preparation of ultrafine SrY2S4:Eu2+ phosphor by carbonate precursor and CS2 sulfurizationCarbonate coprecipitation precursors were perpared by mixed nitrates solution including Si*+,Y3+ and Eu3+ as cation solution and (NH4)2CO3 as precipitator. TG-DSC curves indicated that the composition of coprecipitation changed from Sr(Eu2)Y2(OH)2(CO3)3-niH2O to Sr(Eu2)Y2(CO3)4-w2H2O when the concentration of (NEL^CCb varied from low to high. Red SrY2S4:Eu2+ phosphors were synthesized by carbonate coprecipitation precursors and CS2 sulfurization. XRD showed pure SrY2S4 crystalline was formed so long as the calcining temperature was above 800 °C. Fluorescent spectra and the SEM data indicated that the emission intensity was the strongest and the diameter of the ellipsoidal particles were smaller than 1 um when the precursor prepared under the condition of [Sr(NO3)2+Eu(NO3)3]: [Y(NO3)3]: [(NH4)2CO3]=0.25 M: 0.50 M: 2.00 M was calcined at 1050 °C for 4 h. The optimum doping concentration for Eu2+ was determined to be 0.6% molar fraction of Sr2"1" in SrY2S4 host lattices.2. Red luminescent properties of Sri.xMxY2S4:Eu2+(M=Ca, Ba)At this chapter we changed the phosphor hosts in order to alter the luminescent properties of SrY2S4:Eu2+ by alkaline metal doping to form new phosphors with the formula Sri.xMxY2S4:Eu2+(M=Ca, Ba). With the molar fraction of Ba2+ increasing, the emission value of Sri.xBaxY2S4:Eu2+(0