Preparation And Luminescence Properties Of Red Phosphor For Warm White LED

In recent years, white LED possessing many advantages,such as long using time, environmental protection and security and energy saving, has become a hot spot of research. At present, white LED is limited to the further indoor lighting applications because of a lack of red phosphor composition, so seeking novel red phosphor for warm white LED has great theoretical value and practical significance. Cubic ZrW₂O₈:Eu³⁺ and hexahedron K2 Ti F6:Mn⁴⁺ red phosphor have been prepared by the mild hydrothermal method and co-precipitation method, respectively, and could be promising red phosphors for generating white light in phosphor-converted warm white light-emitting diodes.The main research content is as follows:Cubic ZrW₂O₈:Eu³⁺ phosphors（about 60 nm, nanorod） are obtained by the hydrothermal method in acid/alcohol mixtures. By analysis the different Eu3+ doping concentrations effect on phase and luminescence properties, it has been found that: the optimum Eu3+ doping concentration is 9 mol%; Eu3+ ions have been doped into Zr W2O8 host lattice,substituted for the C1 low symmetry without inversion center of Zr4+ site; under the 466 nm excitation, intense red emission peaks around 616 nm corresponding to 5D0-7F2 transition of Eu3+ are obsreved. It has been reported by studing emission spectra and fluorescence decay curves of typical sample mearused at different low temperature（10-320 K） that the values of intensity parameter Ω2,4 caculated by JO parameters are 17.82×10-20 and 1.092×10-20 cm2, respectively; when the measured temperature is 10 K, tthe emission intensity of Zr W2O8:9 mol% Eu3+ is the most intense; ZrW₂O₈:Eu³⁺ red phosphor has high quantum efficiency（83.5% under the condition of room temperature） and appropriate color coordinate.K₂TiF₆:Mn⁴⁺ red phosphors（wafer with a particle size of about 15-40 μm and the thickness of about 0.6 μm） with different Mn⁴⁺ doping concentrations are obtained by the co-precipitation method. It has been found by studing on the crystal structure of K2 Ti F6 and the lateral displacement of XRD patterens that Mn⁴⁺ is easy substituted for Ti4+ with local site symmetry of D3 d and introduced into the host material of K2 Ti F6. The crystal structure and vibronic modes of K2 Ti F6:Mn⁴⁺ are investigated by Infrared spectra and Raman spectra, which prove that RL, ν1 and ν5 modes are existed in the powders. By analysing the different Mn⁴⁺ doping concentrations effect on phase and luminescence properties, it has been found that: the half-width at half-maximum of the 470 nm band for K2 Ti F6:Mn⁴⁺ is between 41 and 63 nm; samples give intense red emission peaks at about 630 nm（2Eg-4A2）; the characteristics of broadband excitation and narrowband emission of Mn⁴⁺ are explained through the Tannbe-Sugano energy level diagram; the optimum doping concentration of Mn⁴⁺ is 2.48 mol%（ICP）; 2Eg level follows bi-exponential behavior（3.91 mol%） from monoexponential behavior（0.09-3.00 mol%） with Mn⁴⁺ doping concentrations increasing.It is found by studying the influencing of adding NH4 F on Mn⁴⁺ doping efficiency that:is pure hexahedron phase, when the mole ratio of NH4 F and KMn O4 is 19:1, and it lead to Mn⁵⁺ and Mn²⁺ by adding less and excess NH4 F, respectively. Compared with the corresponding samples without NH4 F, samples adding NH4F:Mn⁴⁺ concentration by means of ICP is increased to 15.1mol% from 2.48 mol%, corresponding to 30 mol% of Mn⁴⁺ ions in the precursor solution, and NH4 increases Mn⁴⁺ doping efficiency greatly; excitation and emission spectrum intensity are greatly increased; the powder is more yellow and smaller; the sample follows monoexponential behavior and decay time is also increased accordingly.