Highly efficient Ce3+ → Tb3+ energy transfer induced bright narrowband green emissions from garnet-type Ca2YZr2(AlO4)3:Ce3+,Tb3+ phosphors for white LEDs with high color rendering index
Inorganic phosphors play an important role in realizing high-performance white light-emitting diodes (LEDs), and thus highly luminescent phosphors with excellent optical properties are urgently needed. In this paper, novel Ce3+/Tb3+ co-doped Ca2YZr2(AlO4)3 (abbreviated as: CYZA) green-emitting phosphors with broadband excitation and high quantum efficiency were synthesized for potential application in white LEDs, and their phase purity, crystal structure, morphology, photoluminescence properties, energy transfer mechanism, and thermal stability were systematically investigated. It was found that the CYZA:Ce3+,Tb3+ phosphors exhibited two broad excitation bands in the 300–470 nm wavelength range, due to the highly efficient energy transfer from Ce3+ to Tb3+ ions. Under the excitation wavelength of 408 nm, the CYZA:Ce3+,Tb3+ phosphors showed bright green emissions around 492, 543, 591, and 628 nm originating from the 5D4 → 7FJ (J = 6, 5, 4, and 3) transitions of Tb3+ ions. The optimal doping concentrations of Ce3+ and Tb3+ ions in CYZA:xCe3+,yTb3+ phosphors were determined to be x = 0.04 and y = 0.9, respectively. The CIE coordinates and the internal quantum efficiency of the composition-optimized CYZA:0.04Ce3+,0.9Tb3+ phosphors were measured to be (0.342, 0.545) and 56%, respectively. The full width at half-maximum (FWHM) of the dominant green emission band around 543 nm was only about 13.5 nm. Finally, a white LED lamp was fabricated using a 400 nm LED chip together with a phosphor blend of blue-emitting BaMgAl10O17:Eu2+, green-emitting CYZA:0.04Ce3+,0.9Tb3+ and red-emitting CaAlSiN3:Eu2+, which produced warm white light with color coordinates of (0.419, 0.392), excellent color rendering index of 91, correlated color temperature of 3233 K, and luminous efficacy of 30 lm W−1 when driven by a 40 mA current. The above results demonstrated that CYZA:0.04Ce3+,0.9Tb3+ can be a potential green-emitting color converter for white LEDs.