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 SmPO 4 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 H-6(5/2) -> P-6(5/2), and is then relaxed to (4)G(5/2) . It jumps from (4)G(5/2) to the lower levels corresponding to the emissions of Sm3+; meanwhile, the transfers from (4)G(5/2) state of Sm3+ ion to D-5(0) state of Eu 3+ ion come out. The mechanism of energy transfer (Sm3+ -> Eu3+) is proved to be dipoledipole interaction with a calculated R c of 9.717 A, 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. (C) 2018 Elsevier B.V. All rights reserved.