A white light emitting phosphor Sr1.5Ca0.5SiO4:Eu3+, Tb3+, Eu2+ for LED-based near-UV chip: Preparation, characterization and luminescent mechanism

In this work, we report preparation, characterization and luminescent mechanism of a phosphor Sr 1.5 Ca 0.5 SiO 4 :Eu 3+ ,Tb 3+ ,Eu 2+ (SCS:ETE) for white-light emitting diode (W-LED)-based near-UV chip. Co-doped rare earth cations Eu 3+ , Tb 3+ and Eu 2+ as aggregated luminescent centers within the orthosilicate host in a controlled manner resulted in the white-light phosphors with tunable emission properties. Under the excitation of near-UV light (394 nm), the emission spectra of these phosphors exhibited three emission bands: one broad band in the blue area, a second band with sharp lines peaked in green (about 548 nm) and the third band in the orange–red region (588–720 nm). These bands originated from Eu 2+ 5d→4f, Tb 3+ 5 D 4 → 7 F J and Eu 3+ 5 D 0 → 7 F J transitions, respectively, with comparable intensities, which in return resulted in white light emission. With anincrease of Tb 3+ content, both broad Eu 2+ emission and sharp Eu 3+ emission increase. The former may be understood by the reduction mechanism due to the charge transfer process from Eu 3+ to Tb 3+ , whereas the latter is attributed to the energy transfer process from Eu 2+ to Tb 3+ . Tunable white-light emission resulted from the system of SCS:ETE as a result of the competition between these two processes when the Tb 3+ concentration varies. It was found that the nominal composition Sr 1.5 Ca 0.5 SiO 4 :1.0%Eu 3+ , 0.07%Tb 3+ is the optimal composition for single-phased white-light phosphor. The CIE chromaticity calculation demonstrated its potential as white LED-based near-UV chip.