Synthesis, photoluminescence, energy transfer and thermal stability of SmPO4@SiO2:Eu3+ core-shell structured red phosphors for WLEDs

A kind of novel core-shell structured nanophosphor material with the average particle size of 85 nm consisting of SmPO4 core encapsulated in Eu3+ doped silica (SiO2: Eu3+) shell has been successfully synthesized by sol-gel hydrothermal method. The details of core-shell structure have been confirmed by X-ray diffraction, high-resolution TEM, BET, FTIR and XPS. Our as-synthesized SmPO4@SiO2:Eu3+ phosphors show strong absorption, high color purity, and relatively high quenching temperature. The optimum Eu3+ doping concentration is determined to be 0.13 mol%. When Sm3+ is excited (401 nm), the electron is excited from 6H5/2 → 6P5/2, and is then relaxed to 4G5/2. It jumps from 4G5/2 to the lower levels corresponding to the emissions of Sm3+; meanwhile, the transfers from 4G5/2 state of Sm3+ ion to 5D0 state of Eu3+ ion come out. The mechanism of energy transfer (Sm3+ → Eu3+) is proved to be dipole-dipole interaction with a calculated Rc of 9.717 Å, and with relatively stable color coordinates. The quenching temperature (T0.5) of the emission spectra reveals that SmPO4@SiO2:Eu3+ core-shell structured phosphors possess stable emission up to 433 K, and the relatively high activation energy (0.204 eV) confirms that the phosphor has good thermal stability. The calculated CIE coordinates for the optimized phosphor are in the deep red region (x = 0.6255, y = 0.374). with high color purity approaching 100%. The as-synthesized SmPO4@SiO2: (0.13 mol%) Eu3+ core-shell structured red nano-phosphor shows good application prospective for n-UV LEDs.