Energy transfer between two luminescent centers and photoluminescent properties of Ca4-yLa6(AlO4) (SiO4)6-O1-/2: yEu2+apatite structure phosphors

ABSTRACT Green-emitting, apatite structure of Ca4-yLa6(AlO4)x(SiO4)6-xO1-x/2: yEu2+ was synthesized by using the high-temperature solid-state method under reducing atmosphere (90%N2-10%H2). Corresponding to the Eu2+ of 4f65d1→4f7 transition at the excitation wavelength of 335 nm, a broadband emission of 450-700 nm showed. Eu2+ lattice selection in Ca4-yLa6(AlO4)x(SiO4)6-xO1-x/2: yEu2+ phosphor were discussed conjunction with apatite crystal structure characteristics. The design of (AlO4)5-/(SiO4)4- various ratios and Eu2+ doping concentration improved the Eu2+ luminous intensity and the red-shift of optical emission spectra. Energy transfer between the two luminescent centers of Eu(I) and Eu (II) happened, and clearly distinguished by photoluminescence decay curves monitored at 480 nm and 560 nm with the average-lifetime (τ) of Eu(I) are 240.5 ns, Eu (II) are 405.3 ns, respectively. The temperature-dependent emissions along with blue-shift phenomenon were addressed through the transition process of energy level. Eu(I) and Eu(II) lattice sites.