Energy transfer and color-tunable luminescence properties of Dy3+ and Eu3+ co-doped Na3Sc2(PO4)(3) phosphors for near-UV LED-based warm white LEDs

Dy3+ singly doped and Dy3+/Eu3+ co-doped Na3Sc2(PO4)(3) phosphors were synthesized by high temperature solid-state reaction and their photoluminescence properties were investigated. The prepared phosphors have a single phase trigonal structure of Na3Sc2(PO4)(3) and consist of micro-particles with an average particle size about 13.8 mu m. Among all the Na3Sc2(PO4)(3):xDy(3+) samples, 5 mol% of Dy3+ ions is found to be optimum concentration because it shows strongest emission intensity under 350 nm excitation. Under 350 nm excitation, the emission spectra of Na3Sc2(PO4)(3):0.05Dy(3+),yEu(3+) phosphors are composed of several bands associated with the transitions of both Dy3+ and Eu3+ ions from the F-4(9/2) and D-5(0) excited states, respectively. It is noticed that integrated emission intensities of Dy3+ ions were decreased with the increase of Eu3+ ion concentration due to energy transfer from Dy3+ to Eu3+ ions. The Dexter theory and Reisfield's approximation were employed to analyze the energy transfer mechanism and it is found that the dipole-dipole interaction is responsible for energy transfer from Dy3+ to Eu3+ ions. Among the Na3Sc2(PO4)(3):0.05Dy(3+),yEu(3+) phosphors, 5 mol% of Dy3+ and 20 mol% of Eu3+ are found to be optimum concentrations because it emits strong warm white light under 350 nm excitation. Further, the quantum efficiency, lifetime, energy transfer efficiency and correlated color temperature (CCT) values of the present phosphors were estimated and compared with the other reported phosphors.