Papers by Keyword: Yellow Phosphor

Abstract: The YAG:Ce³⁺, Gd³⁺/La³⁺ yellow phosphors were prepared by co-precipitation method with 0.1mol/L ammonium bicarbonate and aqueous ammonia as precipitants, and the crystal structure, morphology, luminescent properties were investigated. The results indicated that the emission peaks of the YAG:Ce³⁺, Gd³⁺/La³⁺ were redshifted from 535nm to 545.5nm /547nm, and the relative emission intensity declined from 330nm to 145/132 with doping content of Gd³⁺ /La³⁺ increased from 0 to 0.9mol at room temperature. Compared with Gd-doping phosphors, the redshift of La³⁺-doping phosphor was larger and the relative emission intensity declined more quickly. Compared with YAG:Ce³⁺, the thermal quenching characteristics of YAG:Ce,Gd and YAG:Ce,La were noticeably worse when the temperature increased, but the extents of peak wavelength redshifts were almost the same, about is 7-8nm in the experimental temperature range (50-200°C), have little relation with the doping concentration change. Doping concentrations of Gd or La couldn't be too high, and the suitable concentration was less than 0.6mol at the regulating color temperature and color index.

Abstract: Ce³⁺ activated terbium aluminum garnet ((Tb_1-xCe_x)₃Al₅O₁₂, 0≤x≤0.05) phosphors have been converted from their precursors synthesized via co-precipitation from mixed solutions of aluminum and rare earth nitrates with ammonium hydrogen carbonate (AHC) as the precipitant. Detailed characterizations of the precursors and the phosphor oxides were performed by the combined techniques of X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FE-SEM), differential scanning calorimetry/thermogravimetry (DSC/TG), and photoluminescence spectroscopy. The co-precipitated precursors possess a general composition of (NH₄)_x(Tb,Ce)₃Al₅(CO₃)_y(OH)_z·nH₂O, and the particles, having diameters of about 50nm, are well dispersed. Calcining the precursors at 1000°C for 4 h in the air and then reducing in a hydrogen atmosphere at 1000°C for 2 h yielded a phase pure garnet solid-solution of (Tb_1-xCe_x)₃Al₅O₁₂. The cubic lattice of garnet allows the Ce³⁺ activators to reside at the dodecahedral interstitial sites. The resultant garnet phosphors with various Ce³⁺ contents exhibit nearly identical positions of the PLE/PE bands, but significantly different intensities. Upon blue-light excitation at 470nm, the garnet phosphors exhibit broad band emissions peaking at 560nm. The garnet phosphors show a luminescence quenching concentration of 1.5at% for Ce³⁺.

Abstract: We prepared the surface mounted white light emitting diode (LED) chips by using yellow phosphors on the blue LED chip. The optical and electrical properties of prepared white LED chips were investigated. The yellow phosphor mixed with transparent epoxy was coated on the prepared LED chip. The optimum mixing conditions with epoxy and yellow phosphor is obtained at the mixing ration of epoxy: yellow phosphor = 97 : 3 wt %. The maximum luminance and light emitting efficiency are above 80,000 cd/m2 and 23.2 lm/W, respectively, at the bias voltage of 2.9 V. There was no distinct change in the luminance strength with changing of the yellow phosphor ratios. The flowing current of the white LED chip is about 30 mA at 2.9 V.