Wide excitation-band particle phosphors of rare earth-doped silicate host for WLEDs

A particle phosphors with stoichiometric Sr_xM_2-xSiO₄ (M=Ca, Mg, Ba, x=0-2) for WLEDs (white light emission diode) is prepared by spray-pyrolysis two-step process from rare-earth doped composite sol precursor. Employing the Van Uitert formula, the position of lower d-band edge of Eu²⁺ is calculated from microstructure parameters of Sr_xCa_2-xSiO₄ system for prediction. The typical wavelengths of effective excitation of alkaline earth silicate hosts like Sr_xCa_2-xSiO₄, Sr_xMg_2-xSiO₄ and Sr_xBa_2-xSiO₄ phosphors lie in a wider range from 350 to 460 nm, while the typical emission peak locates at around 562 nm. By comparing the calculated wavelengths in different coordinate number of cations with the measured values of samples, we concluded that all substitutions of the luminescent center of Eu²⁺ in Sr_1.8Ca_0.2SiO₄ for the position of Sr²⁺ are in a six-coordinated atomic position. This rare-earth doped silicate phosphor is of a self-assembly, hierarchical structure from nano-crystal or nano-particulate to submicron size in turn. This particle phosphors featured in a wider wavelength range of excitation could be one of the important candidate phosphors for power, high-brightness and higher CRI white LEDs applications.