The Preparation And Luminescence Properties On The Rare Earth Ions Doped Materials For W-LED

In recent years, white LED (white light emitting diode, W-LED) become a research hotspot for its energy-saving, environmental protection, high efficiency, long life and other advantage. As one of the key members of the "green light", the white LED is expected to replace the traditional incandescent and fluorescent lamps to become a new generation of solid-state lighting source. In this paper, we discuss rare earth ions doped phosphate glass and glass-ceramic materials for white LED. Compared with the powder light-emitting materials, luminescent glass and glass-ceramic materials have many advantages, such as low manufacturing costs, less halo effect, great light stablity, easy to package, tunable, good thermal stability and high efficiency. Among glass materials, phosphate glass has its own advantages:such as low scattering, high refractive index, high rare earth doping concentration and large emission cross section width and UV permeability. In this paper, we prepare phosphate glass and glass-ceramic, select the appropriate rare earth luminescent ions, make use of the up-conversion luminescence and the down-conversion luminescence of the different rare earth ions doped materials to obtain high-quality white light.We prepare rare earth ions such as Tm3+, Tb3+, Dy3+, Er3+, Yb3+, Sm3+, Eu3+single doped or co-doped phosphate glass samples by high temperature melt method. Then we measure the absorption spectra, excitation spectra, emission spectra, fluorescence decay curves and color coordinates of the glass and glass-ceramic samples to analyze the optical performance of the up-conversion and down-conversion luminescent. Based on the above test results, we analyze the energy transfer mechanisms of the rare earth ions in the phosphate samples. In addition, we prepare the Tm3+/Er3+/Yb3+co-doped phosphate glass ceramis sample by heat-treated method. Confirmed by X-ray diffraction, LiYbP4O12Li6P6O18nanocrystals have precipitated in the glass-ceramic. Under the980nm pump wavelength excitation, the up-conversion luminescence intensity of Tm3+/Er3+/Yb3+co-doped phosphate glass ceramic was significantly stronger than that of the glass. The color coordinates of Tm3+/Er3+/Yb3+co-doped phosphate glass ceramics on the conversion luminescence has been calculated in the white area so that it can be satisfied with the requirements of the white LED.In addition, we prepare Tm3+/Dy3+/Sm3+co-doped phosphate glass as well as of Tm3+/Tb3+/Eu3+co-doped phosphate glass and glass ceramic samples with different doping concentration of the rare earth ions. Under the UV excitation, the down-conversion luminescence of them has been analyzied. Experimental results show that with the Sm3+ions concentration increased, blue and green light-emitting intensity of the Tm3+/Dy3+/Sm3+co-doped phosphate glass samples decreases significantly, while the luminous intensity of the red light increased. So we can confirm the energy transfer processes among Tm3+ions, Dy3+ions and Sm3+ions. Similarly, as the Eu3+ion doping concentration increased, the intensity of blue light in the Tm3+/Tb3+/Eu3+co-doped phosphate glass sample is almost constant, the green light-emitting intensity decreases, but the red luminous intensity increased, which confirmed the energy transfer process between the Tb3+ions and Eu3+ions. Based on the measurement of the fluorescence decay curves and the calculation of the luorescence lifetime, we have made a reasonable explanation of the above phenomenas. After heat treatment, the luminous intensity of the Tm3+/Tb3+/Eu3+co-doped phosphate glass-ceramic samples is significantly enhanced. In addition, under the UV excitation, color coordinates of some samples are very close to the standard white lighting color coordinates (x=0.333, y=0.333). Through the research on the sample preparation and characterization, the rare earth ions doped glass and glass-ceramic showed good luminescence properties which are suitable for white LED. Therefore, the rare earth ions doped phosphate luminescent glass and glass ceramic are very potential materials for the development of white LED.