Synthesis And Luminescent Properties Of Alkaline Earth-Rare Earth Ternary Sulfides Red Phosphor

Alkaline-rare earth ternary sulfides MRE₂S₄ (M=Ca, Sr, Ba; RE=La, Y) with bandgaps in the range of 2.3-3.6 eV is a kind of suitable material host. In addition, MRE₂S₄, with the excellent thermal stability, strength and infrared transmission characteristics, make themselves good candidates to be studied for novel IR optical window and luminescence materials. Therefore, there are significance and application value for the study of rare earth ions doping SrY₂S₄ phosphors in the applications of sunlight-conversion, light emitting diodes (LED), electroluminescence (EL) devices.MY₂S₄: Er³⁺, Eu²⁺ (M=Sr, Ba) phosphors whose emission wavelength (663 nm) is almost equal to absorption wavelength of chlorophyll (661 nm) have been discovered, which is considered to have potential application value. Own to the very low absorption intensity of blue-green light, however, these phosphors can not be excited effectively by solar light. Accordingly, it is important theoretical significance and application value to improve the absorption intensity of blue-green light of MY₂S₄: Er³⁺, Eu²⁺ (M=Sr, Ba) phosphors.Ternary sulfides are mainly synthesized by solid state method at high temperature with H₂S or CS₂ reducing atmosphere. Unfortunately, H₂S and CS₂ are poisonous and unable to be used to expand production. So, Looking for a new synthesis method expected to achieve industrial production has important practical significance. In this article, we studied the MY₂S₄: Er³⁺, Eu²⁺ (M=Sr, Ba) phosphors on the basis of the effect of host and rare earth ions on their luminescent properties and synthetic methods. 1. Luminescent properties of rare-earth ions doped ternary compound SrY₂S₄Carbonate precursors were prepared by mixed nitrates solution including Sr²⁺,Y³⁺and RE³⁺ (RE= Eu, Ce, Ho, Pr, Tm, Sm and Er) as cation solution and (NH₄)₂CO₃ as precipitator, red SrY₂S₄: RE³⁺/Eu²⁺ phosphors were synthesized by calcining carbonate coprecipitation precursors with CS₂ reducing atmosphere. The luminescent properties of these phosphors are researched by fluorescent spectra, In addition to SrY₂S₄: Pr³⁺ phosphor whose excitation spectra shows only one excitation band of blue-green zone, excitation spectra of other rare-earth ion doped phosphors consist of the two bands, corresponding to the matrix absorption and f-d or f-f of transition absorption of rare-earth ions, respectively. Emission spectra of SrY₂S₄: Ce³⁺, Eu²⁺ and SrY₂S₄: Ho³⁺ phosphors show two peaks of green and red light, the ratio of both green and red light peaks can be controlled by changing the concentration of Ho³⁺ ion, phosphors doped with other rare earth ions show only one red light emission.2. Preparation and luminescence properties of phosphorsM_1-xZn_xY₂S₄: Er³⁺, Eu²⁺ (M=Sr, Ba)M_1-xZn_xY₂S₄: Er³⁺, M_1-xZn_xY₂S₄: Eu²⁺ and M_1-xZn_xY₂S₄: Er³⁺, Eu²⁺ (M=Sr, Ba) phosphors were prepared by co-precipitation. XRD patterns showed that the synthesized crystalline powders possess the orthorhombic [CaFe₂O₄]-type structure as the Zn²⁺ concentration (x) is less than 20 mol% and 10 mol% in Sr_1-xZn_xY₂S₄ and Ba_1-xZn_xY₂S₄ host, respectively. Emission intensity of M_1-xZn_xY₂S₄ codoped with Eu²⁺+Er³⁺ depends strongly on the Zn²⁺ concentration. With an increase in the Zn²⁺ concentration(x), excitation band set in ultraviolet area (250-413nm) showed red shift and the excitation intensity in the visible light range (413-600 nm) showed increased noticeably. When x is equal to 0.1 mol, compared with that of undoped Zn²⁺ ion, the emission intensity of the SZYSEE and BZYSEE phosphors reaches the maximum which increased by 10.7 and 5.7 times, respectively. Due to the excellent performance of strong and broad absorption of the blue-green zone, red emission with excellent monochromaticity, color of a good launch, good thermal stability and not easy deliquescence, Ba_0.9Zn_0.1Y_1.76S₄:0.24Er³⁺, 0.006Eu²⁺ was considered as a sort of novel red phosphor candidate for agricultural light conversion agents and for white-LED.3. Directly synthesis of ternary sulfides by carbon reduction methodA series of ternary sulfides , MY₂S₄ (M=Sr, Ba), were directly synthesize by carbon reduction method. XRD patterns show that the relatively pure SrY₂S₄ can be fabricated as n_SrSO4: n_Y2(SO4)3: n_C=1 :2:60, T=1200℃, t=12 h and BaY₂S₄ as n_BaSO4: n_Y2(SO4)3: n_C=1:2:60, T=1100℃, t=12 h, and the impurity phase is Y₂O₂S. Appropriately doping Er³⁺ ions contribute to the formation of SrY₂S₄ and BaY₂S₄ phases. We investigated the luminescent properties of Eu²⁺ and Er²⁺ ions. Eu monodoped SrY₂S₄ phosphor show the characteristic transition of Eu²⁺, while Eu monodoped BaY₂S₄ phosphor show the characteristic transition of Eu³⁺. The luminescent properties of Eu, Er co-doped MY₂S₄ (M=Sr, Ba) phosphors synthesized by both carbon reduction and coprecipitation method is the same as. Carbon reduction method is simple and easy to operate, low equipment and non-polluting to the environment, so it is expected to become a method to expand production of ternary sulfides.