Preparation And Luminescence Regulation Of Phosphors For Warm White LEDs

White light LEDs have become the most widely used lighting equipment today due to their environmental friendliness,energy conservation,long-life and small size,especially the conversion type LED is the most common,this type of lighting device is obtained by combinating of LED chips coated with phosphor powder.The commercial whilte LED(blue InGaN chips combines yellow YAG:Ce³⁺phosphors)has the defects of high color temperature(CCT)and low color rendering index(CRI)due to lack of red component.Therefore,this paper adopts the high-temperature solid method to prepare red phosphors for white light LEDs with rare earth Eu³⁺and transition metal Mn⁴⁺as activators,and characterizes its structure and morphology luminescence performance,and explains its luminescence mechanism;The combination of Dy³⁺and Mn⁴⁺is used as an activator to prepare a single matrix white light and evaluate its luminescence performance.The research content and results are as follows,1.Preparing a series of KGd_1-xEu_x(MoO₄)₂ phosphor samples by high-temperature solid method and carry out structural morphology and luminescence performance characterization.It is found that its morphology will be similar with the emission of Eu³⁺doping content;Its monitored 614 nm excitation spectrum consists of a broad excitation band centered at 277 nm and several narrow peaks.They are the characteristic peaks of the charge transfer band between Eu³⁺-O^2-and the 4f-4f electron radiation transition of Eu³⁺;The emission spectra are composed of three weak peaks and one strongest peak at 614 nm.These emission The peak comes from the5d-7f energy level transition of Eu³⁺.The fluorescent emission emitted by this series of phosphors does not appear to luminous concentration quenching,and its spectrum shows that Eu³⁺doped molybdate is suitable for improving the performance of commercial white light LEDs.2.A series of CaAl_12-xO₁₉:x Mn⁴⁺red phosphors were synthesized by high-temperature solid method.The XRD results are CaAl₁₂O₁₉ pure phase,and the phosphor morphology was polygonal particles of about 10 micrometers.When the wavelength of the monitoring light is654nm,the excitation spectra of all phosphor samples show a continuous broad spectrum from220 to 550 nm,with peaks at 340,383 and 472 nm,which are resulted from the spin-allowed⁴A_2g-⁴T_1g,⁴A_2g-²T_2g and ⁴A_2g-⁴T_2g transitions of Mn⁴⁺,respectively.The emission spectrum of the phosphor is red light with the main peak at 654 nm,which comes from the ²E_g-⁴A₂energy level transition of Mn⁴⁺ion.When x=0.012,the luminous intensity of this series of red phosphors reach to maximum,if the Mn⁴⁺concentration exceeds this value,it shows the phenomenon of concentration quenching.By calculating the critical distance of the Mn⁴⁺ion of the CaAl_12-xO₁₉:x Mn⁴⁺sample,it is 35.99?.Using Dexter theory to analyze the concentration of the phosphor,it is concluded that the concentration quenching mechanism causes by o the dipole-dipole interaction in the electrical multilevel interaction of CaAl_12-xO₁₉:x Mn⁴⁺phosphor.3.The Ca_1-y-zAl_11.988O₁₉:0.012Mn⁴⁺/y Zn²⁺/z Mg²⁺series of samples were prepared by the high-temperature solid method,and the excitation and emission spectra did not change significantly compared to the just dop Mn⁴⁺.The phosphor has the maximum luminous intensity when y=0.08.Zn²⁺improves the crystallization of the matrix and promotes the increase of luminous intensity.Doping with Mg²⁺on Ca_0.92Al_11.988O₁₉:0.012Mn⁴⁺/0.08Zn²⁺(CAO:MZ)can further increase the luminous intensity.It is calculated that the crystal field value(Dq/B)of Ca_0.88Al_11.988O₁₉:Mn⁴⁺/0.08Zn²⁺/0.04Mg²⁺(CAO:MZM)phosphor is 2.60,and the electron cloud arrangement ratio?1 is 1.004.Mg²⁺increases the luminous intensity of CAO:MZM phosphors,and Mg²⁺plays a role in charge compensation.The average lifetime(?)of CAO:M,CAO:MZ and CAO:MZM phosphors are 1.078,1.042 and 1.035 ms,respectively.The chromaticity coordinates(CIE)of the red LED made of CAO:MZM phosphor is(x,y)=(0.6434,0.2575).Assemble it with a blue LED chip and YAG:Ce³⁺yellow phosphor to assemble a white LED.At a current of 20m A,the color temperature(CCT)of the white LED containing CAO:MZM phosphor is 4672K,the color rendering index(CRI)is 80,The white LED color temperature is5843K,and the color rendering index is 74.4,which is wihout CAO:MZM phosphor.CAO:MZM phosphor can effectively reduce the color temperature of commercial white LEDs and increase the color rendering index.4.A series of Ca_1-m-nAl_11.988O₁₉:0.012Mn⁴⁺/m Dy³⁺/n Mg²⁺phosphors were prepared by high temperature solid method and then characterized them.XRD phase characterization is CaAl₁₂O₁₉pure phase.The luminescence is under monitoring when the light wavelength is 475,518 and571nm,the peaks appear at 353 nm,365 nm and 390nm.Under 353nm ultraviolet excitation,the emission spectrum consists of a peak at 475 nm,a weak peak at 518nm,peak at 571nm and654nm.Explain the reason of energy transfer between Dy³⁺and Mn⁴⁺.Doping with Mg²⁺can regulate the spectrum of CaAl₁₂O₁₉:0.012Mn⁴⁺/0.06Dy³⁺phosphors.Under the excitation of353nm ultraviolet,the CIE coordinates of the CaAl₁₂O₁₉:0.012Mn⁴⁺/0.06Dy³⁺phosphors excited light are located at(x,y)=(0.3455,0.3765),which belongs to the range of white light.The luminosity and color coordinates corresponding to the spectrum show that the CaAl₁₂O₁₉:0.012Mn⁴⁺/0.06Dy³⁺/0.035Mg²⁺phosphor can be used as a single matrix white light.