Preparation And Luminescence Properties Of The Phosphor For White LED

White LED(w-LED), which is so called the next general lighting,is a topic of increasing interest due to their high luminous efficiency, low power consumption, environment friendly, reliability, long life and so on. The phosphor-converted -LED (pc-LED) method which connects InGaN LED with the phosphor is most common. So the phosphor for White LED is a novel topic of increasing interest. The common way to fabricate w-LED device is using YAG:Ce as a broad band yellow phosphor coated on the blue LED chip. However, there exist a drawback in this combination, viz., the output white light is deficient in the red region of the visible light spectrum (above 600 nm). To solve these problems, one of the following attempts was generally applied: 1) dope some desirable cations in YAG:Ce³⁺ lattice to slightly adjust emission wavelength through crystal lattice change, 2) obtain novel phosphors for white LED.In the paper, the doping of yellow phosphors (YAG: Ce) has been well investigated, and the phosphors for white LED has been obtained, which could be excited by UV or n-UV light. In addition, the synthesis methods, luminescence Properties and luminescence intensity also has been studied detailedly. Therefore, we have obtained the solutions as following:1) The amount caused the phase transferring in (Y0.96-xLnxCe0.04)3Al5O12 decreases with the increasing of the ionic radii of the doping lanthanide ions (La³⁺: 0.106nm, Gd³⁺: 0.094nm, Lu³⁺:0.083nm). In the system of (Y0.96-xLaxCe0.04)3Al5O12, when x increase to 0.5, the LaAlO3 phase becomes the main one. In the system of (Y0.96-xGdxCe0.04)3Al5O12, when x reaches 0.9, the orthorhombic GdAlO3 one becomes the main phase. However, in the system of (Y0.96-xLuxCe0.04)3Al5O12, when Lu³⁺ ion entirely substitutes for Y³⁺ ion, its structure is unchanged.Additionly, the doping effects of La³⁺, Gd³⁺ and Lu³⁺ on the crystal structure and luminescence properties of (Y0.96-xLnxCe0.04)3Al5O12 (Ln=Gd, La, Lu) phosphors were studied. The X-ray diffraction patterns present that with the increasing of doping concentrations of La³⁺ and Gd³⁺ ions, the d-value of (Y0.96-xLnxCe0.04)3Al5O12 (Ln=Gd, La) increases; and the larger the doping ion, the stronger the effect is. With the increasing of the doped Gd³⁺ concentration, the main emission band of (Y0.96-xGdxCe0.04)3Al5O12 shows a red shift character; and the intensities for both emission and excitation bands become weaker. The main emission band moves from 536nm to 553nm when the value of x changes from 0 to 0.7. The red shift of the emission band of the phosphors resulting from doping of Gd³⁺ ion in YAG:Ce is in favor of obtaining good color balance for the above w-LED. But the main emission band of (Y0Lu0.96Ce0.04)3Al5O12 shows a blue shift character.2) (Y0.95Ln0.01Ce0.04)3Al5O12 phosphors were synthesized by high-temperature solid state reaction under reducing atmosphere and the doping effects of lanthanide ions (Ln³⁺) on the luminescence properties of phosphors were studied. The excitation and emission spectra of YAG:Ce,Ln show that the influence between Ce³⁺ and Ln³⁺ can be divided into three types. (1) The Ce³⁺ emission intensities are decreased slightly in the YAG:Ce doped with La³⁺, Gd³⁺ and Lu³⁺, respectively. (2) Because of the energy transfer and competitive absorption, when Pr³⁺, Sm³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺ co-doped YAG:Ce, the Ce³⁺ emission intensities are observably decreased. In the YAG:Ce,Pr system, the emission of Pr³⁺ is at 609 nm; and in the YAG:Ce,Sm system, the emission of Sm³⁺ is at 616 nm. So it can increase the color rendering index (CRI) of YAG:Ce doped with Pr³⁺ or Sm³⁺. (3) It was found that doping with Eu³⁺, Yb³⁺ and Nd³⁺in YAG:Ce the Ce³⁺ emission intensities quenched strongly.Phosphors were synthesized by high-temperature solid-state reaction under reducing atmosphere. The X-ray diffraction patterns presented Pr³⁺ and Sm³⁺ can partially replace Y³⁺ and the phase is unchanged. The doping effects of Pr³⁺ and Sm³⁺ on the luminescence properties and fluorescence lifetimes of (Y0.96-XLnXCe0.04)3Al5O12 (Ln= Pr³⁺,Sm³⁺) were studied. The emission and excitation spectra of samples are recorded. In the (Y0.96-XPrxCe0.04)3Al5O12 system the emission band of Pr³⁺ was at about 609nm; and in the (Y0.96-XSmxCe0.04)3Al5O12 system the emission band of Sm³⁺ was at about 616nm. So it can increase the color rendering index (CRI) of YAG:Ce phosphors by doped Pr³⁺ or Sm³⁺. Fluorescence lifetimes of the Ce³⁺ in (Y0.95Pr0.01Ce0.04)3Al5O12, (Y0.95Sm0.01Ce0.04)3Al5O12, (Y0.96Ce0.04)3Al5O12 are measured. The lifetime decreased doping of Pr³⁺or Sm³⁺ in YAG:Ce³⁺.3)SrCaSiO4:Eu³⁺ was synthesized by high temperature solid state reaction and the X-ray diffraction patterns analysis confirmed the formation of orthorhombic SrCaSiO4:Eu³⁺. The spectra results show that the phosphor can be efficiently excited by UV LED and exhibit red emission. The effects of the doped-Eu³⁺ concentration in SrCaSiO4:Eu³⁺ on the emission spectra are investigated in detail. The results present that the quenching concentration (χc) of Eu³⁺ in SrCaSiO4 phosphors is about 10mol%, and the critical transfer distance (Rc) is about 12?. The lifetime decay curves of the 592nm emission in SrCaSiO4:Eu³⁺ phosphor, and the fitting results reveal that the lifetime of 592nm emission of Eu³⁺ in the SrCaSiO4 phosphor is about 3ms.4)A novel green emitting phosphor SrCaSiO4:Eu²⁺,Ce³⁺ for white light emitting diodes. Excitation spectrum of this sample shows a broad band range from 250nm to 400 nm which is well agree with the spectrum of diffuse reflectance, thereby, it could absorb ultraviolet effectively, and used as phosphors for white light emitting diodes using UV LED. Emission spectrum of SrCaSiO4 :Eu²⁺,Ce³⁺ is a broad band covering the blue-green to yellow region with a maximum at 500nm .There is energy transfer between Ce³⁺ and Eu²⁺ in SrCaSiO4:Ce³⁺,Eu²⁺. It is found that the substitution of 1% Ce³⁺ atoms instead of the strontium greatly enhance the 500 nm emission, especially for the excitation wavelength range from 320 to 370 nm.For the SrCaSiO4:Eu²⁺ phosphor, the highest intensity of SrCaSiO4:Eu²⁺ phosphor was achieved when the concentration of Eu²⁺ were 0.5mol % of the strontium. The obtained critical distance (Rc) value is about 33 ?Lifetime decay curves are measured and can be fitted successfully based on the well known exponential equation. The decay lifetime for Eu²⁺ is increase when dope with Ce³⁺, however, The decay lifetime for Ce³⁺ is decrease.5)During the synthesis pure M-BaAl₂Si₂O₈:Eu,Mn, we have imported nearly pure M-BaAl₂Si₂O₈:Eu,Mn10% which has been synthesized by ourself, for it is difficulte to synthesis the pure M-BaAl₂Si₂O₈:Eu,Mn.The emission spectra as probe examine the structure of simples. Because the excitation sprectra of M–BaAl₂Si₂O₈:Eu and H–BaAl₂Si₂O₈:Eu have strong peaks at 330nm, the emission sprectra of M–BaAl₂Si₂O₈:Eu and H–BaAl₂Si₂O₈:Eu can be tested under 330nm excitation. So the emission could be used to analyze the structure of the simples. A novel green emitting phosphor M–BaAl₂Si₂O₈:Eu,Mn for white light emitting diodes. Excitation spectrum of this sample shows a broad band range from 250nm to 360 nm, thereby, it could absorb ultraviolet effectively, and used as phosphors for white light emitting diodes using UV LED. Emission spectrum of M–BaAl₂Si₂O₈:Eu,Mn is a broad band with a maximum at 440nm and a broad band at 550nm.There exists energy transfer between Eu²⁺ and Mn²⁺ in M–BaAl₂Si₂O₈:Eu,Mn. In the M–BaAl₂Si₂O₈:Eu,Mn system, With the increasing of the co-doped Mn²⁺ concentration, the emission band of Eu²⁺ (440nm)decrease, and that of Mn²⁺(550nm) increase.