Preparation And Luminescent Properties Of Sr₃Ga₂O₅Cl₂ Red Phosphor For White LED

As the fourth generation lighting source, white LED have many advantages, such as energy saving, environmental protection, safety and reliability, long lifetime, attracting wide attention of researchers. White LED obtains white light through the light conversion method. Efficient red phosphor has become a hot spot in the current research of white LED, as it’s indispensable to the composition of high quality white light. The traditional white LED coated yellow phosphor on the blue light LED chip, has the low color rendering index, for the absence of red phosphor. At present, using UV LED chip exciting RGB phosphor is the development trend of white LED, it has excellent luminous performance. However, as the main red phosphor, sulfur oxide has poor chemical stability, and can’t absorb UV/near UV light effectively. So, it’s important to study a new type of red phosphor, which has efficient absorption in the (near) UV spectrum range.Sr3Ga2O5Cl2 red phosphor was prepared by high temperature solid state method, the luminescent center of the phosphor is Sm3+ and Eu3+, related research results are as follows:(1) Studying the technological conditions of the preparing of Sr3Ga2O5Cl2 red phosphor powder systematically. The optimum synthesis condition is calcinating at 700℃ for 10h, grinding 45min after natural cooling, and then calcinating at 1100℃ for 6h again. Scanning electron microscopy (SEM) was used to test the morphology of the phosphor samples, the sample is composed of irregular shape crystals, and the distribution of powder particles is even, the average size is about 5um. The effective excitation wavelength of Sr3Ga2O5Cl2: Eu3+ red phosphor is 301 nm, which attributing to the charge transition of O2" â†'Eu3+. Under 301 nm UV excitation, the emission spectrum of the phosphor Sr3Ga2O5Cl2:Eu3 has two peaks, attributing to 5D0â†'7F1 (588nm) transition and 5D0â†'7F2(617nm) transition. The luminescence intensity of Sr3Ga2O5Cl2:Eu3+ red phosphor increases with the increase of Eu3+ concentration first and then decreases, the optimum doping concentration is 7.0mol%. In order to evaluate the luminescent properties of red phosphor Sr3Ga2O5Cl2:Eu3+, we compared it with the traditional commercial phosphor Y2O3:Eu3+, the electric dipole transition strength of Sr3Ga2O5Cl2:Eu3+ is close to Y2O3:Eu3+.(2) The X-ray diffraction pattern (XRD) of Sr3Ga2O5Cl2:Sm3+ have been tested, Sr3Ga2O5Cl2 has single structure, the space group is P21, the lattice constant is a=b=c=0.9569nm, the doping of Sm3+ substitutes the Sr2+ sites to form the emission center. The excitation spectrum is composed of the charge transfer band centered at 230nm and the characteristic excitation transition of Sm3+. The characteristic emission transition of Sm3+ is 4G5/2â†'6H5/2(565nm),4G5/2â†'6H7/2(601nm) and 4G5/2â†'6H9/2(650nm). The color coordinates of phosphor is (0.55,0.45), according to the calculation by CIE1931, which belongs to the category of orange light. The luminescence intensity of Sr3Ga2O5Cl2:Sm3+ increases at first and then decreases with the increase of Sm3+ concentration. The concentration quenching phenomenon appeared, once the concentration of Sm3+ exceed 3.0mol%. According to Blasse and Dexter theory, we analyzed the reason of concentration quenching, its mechanism is the electric dipole-dipole interaction.