Efficient green-emitting Ca2GdZr2Al3O12:Ce3+,Tb3+ phosphors for near-UV-pumped high-CRI warm-white LEDs

Abstract

In this work, we reported novel efficient Ce3+/Tb3+ co-doped Ca2GdZr2Al3O12 (CGZA) green-emitting phosphors by traditional solid state method. The phase purity, crystal structure, morphology, photoluminescence properties, internal quantum efficiencies (IQEs), and thermal stability of the samples were systematically investigated. The obtained results revealed that there was an obvious spectral overlap between the emission spectrum of Ce3+ singly doped CGZA phosphors and excitation spectrum of Tb3+ singly doped CGZA phosphors, and efficient energy transfer from Ce3+ to Tb3+ ions existed in Ce3+ and Tb3+ co-doped CGZA phosphors. The Ce3+→Tb3+ energy transfer mechanism was ascribed to the dipole-dipole interaction. The CGZA:Ce3+,Tb3+ phosphors exhibited a broad excitation spectrum in the wavelength range of 370–470 nm with a maximum at 408 nm corresponding to the spin-allowed 4f-5d transition of Ce3+ ions. Upon near-ultraviolet (near-UV) excitation at 408 nm, the composition-optimized CGZA:0.02Ce3+,0.8 Tb3+ sample showed intense sharp narrow-line emissions at 485, 543, 591, 629, 643, 663, and 679 nm due to the 5D4→7FJ (J = 6–0) transitions of Tb3+ ions, along with a good IQE of 51%. Lastly, a white light-emitting diode (LED) device was fabricated by using as-prepared CGZA:0.02Ce3+,0.8Tb3+ green phosphors, commercial BaMgAl10O17:Eu2+ blue phosphors, and CaAlSiN3:Eu2+ red phosphors, and under 300 mA driven current it gave bright warm-white light with a low correlated color temperature of 3969 K and a high color rendering index (Ra = 91.2). Our work provides a new perspective for the design and fabrication of efficient color conversion materials toward near-UV LED-based warm-white LEDs.