Silicate apatite phosphors for pc-LED applications

Single-phase ceramic samples of silicate apatites [M.sub.2][Ln.sub.8][(Si[O.sub.4]).sub.6][O.sub.2] (M = Mg, Ca, Sr; Ln = Y, La) undoped and doped with [Eu.sup.3+], [Ce.sup.3+], or [Mn.sup.2+] ions were obtained by the high-temperature solid-state reaction technique using precursors synthesized under hydrothermal conditions. The phosphors were characterized by XRD analysis, Raman spectroscopy, and steady-state/time-resolved and site-selective photoluminescence spectroscopy under blue-to-VUV excitation. It is shown that the small-radius [Mg.sup.2+] ions, which can occupy two types of suitable sites in the apatite structure, strongly influence luminescence properties of apatites, in particular the distribution of [Eu.sup.3+] ions between these sites. A bright broad-band yellow emission (peaked at 560 nm with [tau] < 1 [micro]s) was obtained from the [M.sub.2][Ln.sub.8][(Si[O.sub.4]).sub.6][O.sub.2]:Eu apatite after annealing it in a [H.sub.2](15%)/Ar reducing atmosphere. This emission is due to 5d--4f transitions of [Eu.sup.2+] and is efficiently excited by near UV-to-blue light (300-450 nm). Silicate apatites co-doped with optimal concentrations of [Eu.sup.3+]/[Eu.sup.2+] or [Eu.sup.2+]/[Mn.sup.2+] can be considered as possible single-phase phosphors for application in warm white pc-LEDs. Key words: optical materials; luminescence of [Eu.sup.3+], [Eu.sup.2+], [Ce.sup.3+], [Mn.sup.2+]; silicate apatites; pc-LED.