RESUMO
A series of Ce3+-, Tb3+- and Ce3+/Tb3+-doped La3Si8N11O4 phosphors were synthesized by gas-pressure sintering (GPS). The energy transfer between Ce3+ and Tb3+ occurred in the co-doped samples, leading to a tunable emission color from blue to green under the 360 nm excitation. The energy transfer mechanism was controlled by the dipole-dipole interaction. The Ce3+/Tb3+ co-doped sample had an external quantum efficiency of 46.7%, about 5.6 times higher than the Tb-doped La3Si8N11O4 phosphor (8.3%). The thermal quenching of the Tb3+ emission in La3Si8N11O4:Tb,Ce was greatly reduced from 74 to 30% at 250 °C, owing to the energy transfer from Ce3+ to Tb3+. The blue-green La3Si8N11O4:0.01Ce,0.05Tb phosphor was testified to fabricate a warm white LED that showed a high color rendering index of 90.2 and a correlated color temperature of 3570 K. The results suggested that the co-doped La3Si8N11O4:Ce,Tb phosphor could be a potential blue-green down-conversion luminescent material for use in UV-LED pumped wLEDs.
RESUMO
Eu2+-doped La3Si8N11O4 phosphors were synthesized by the high temperature solid-state method, and their photoluminescence properties were investigated in this work. La3Si8N11O4:Eu2+ exhibits a strong broad absorption band centered at 320 nm, spanning the spectral range of 300-600 nm due to 4f7 â 4f65d1 electronic transitions of Eu2+. The emission spectra show a broad and asymmetric band peaking at 481-513 nm depending on the Eu2+ concentration, and the emission color can be tuned in a broad range owing to the energy transfer between Eu2+ ions occupying two independent crystallographic sites. Compared to the Ce3+-doped La3Si8N11O4, the Eu2+-doped one shows a larger thermal quenching, predominantly owing to photoionization. Under 320 nm excitation, the internal and external quantum efficiencies are 44 and 33%, respectively.
RESUMO
Gd2O2S: Eu, Mg, Ti, a novel red long afterglow phosphor, was synthesized in microwave field. The synthesized phosphors were investigated respectively by XRD, SEM and fluorescence spectrophotometer. The results show that Gd2O2S: Eu, Mg, Ti phosphors possess hexagonal crystal structure, which is similar to that of Gd2O2S. The particles of Gd2O2S: Eu, Mg, Ti phosphors are basically spherical in shape, with good dispersing. The mean particle size is 1-2 microm. The excitation spectrum is a broad band and the main peak is at 360 nm. Moreover, excitation peaks at 400, 422 and 472 nm were found in the excitation spectrum. The emission spectrum shows that Gd2O2S: Eu, Mg, Ti has narrow emission peaks. The emission peaks are ascribed to Eu3+ ions transition from 5 D(J) (J = 0, 1, 2) to 7F(J) (J = 0, 1, 2, 3, 4). With the increase in Eu3+ molar ratio, the emission peaks at 586, 557, 541, 513, 498, 471 and 468 nm in the blue and green region weaken gradually relative to the main emission peak at 627 nm. Therefore the red emitting at 627 nm becomes strong gradually. When the molar ratio is 6%, the red emitting becomes the strongest. The Ti and Mg co-doping can obviously improve its long-afterglow property.
