Strong green and red emission of a newly developed calcium fluoroaluminate: Eu3+ phosphor

Abstract

A phase of new bichromatic (green, red) phosphor Ca2Al3O6F:Eu(III), was found to grow in a small fraction along with Ca5(PO4)3F:Eu(III) phase if aluminum is previously added to the reaction mixture of the latter and flourish to a sizable concentration on subsequent heat treatment. The luminescence spectrum of the as-prepared sample, where Ca5(PO4)3F:Eu(III) is the dominant phase, shows a strong band at 612 nm along with a series of less intense bands at 573, 584, 644, and 692 nm due to different 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions and indicates that the presence of aluminum in the system forces the Eu(III) ions to occupy exclusively one type of site rather than multiple types of sites. As the aluminate phase grows, a strong green emission band around 520 nm due to the 5D2 → 7F3 transition of Eu(III) occurs concomitant with a splitting of almost all the 5D0 → 7FJ bands. The excitation spectrum of the green emission (520 nm) shows a strong absorption band at 393 nm, and the electron spin resonance spectrum of this material shows existence of a fluorine-related hole center of (F2n)− type in the matrix. It is argued that the (F2n)− holes are localized in the interstitial of the Ca2Al3O6F phase near the calcium-substituted Eu(III) ions to maintain the charge balance and form a complex with the latter, which plays a vital role in the process of green emission.