Tuning of photoluminescence by mixing valence of Eu2+/Eu3+ in Ca9Ln(PO4)7 (Ln = Y, La) phosphor for UV light-emitting diodes

A series of single-phased emission-tunable Ca9Ln(PO4)7:Eu2+/3+ (Ln = Y, La) phosphors were synthesized by a high temperature solid-state reaction in a CO atmosphere, and its luminescent properties have been investigated. The phosphors can be well excited in the wavelength range of 245–475 nm, which match well with the n-UV chip. Additionally, Eu2+ and Eu3+ ions exist in Ca9Ln(PO4)7: Eu2+/3+ (Ln = Y, La), although the samples are prepared at the reducing atmosphere. The tunable emission colors of the phosphors can be achieved by varying the Eu ion concentration or excitation wavelength. The corresponding color hue of Ca9Y(PO4)7: xEu (x = 0.01–0.2) phosphors shifts gradually from green to white and eventually to orange-red with the Eu concentration increases, whether at 252 nm, 300 nm or 395 nm excitation. While the colour coordinates of Ca9La(PO4)7: 0.08Eu phosphor by changing the excitation wavelength, varied the emission hue of the phosphor from orange-red to yellow-green to white, and eventually back to orange-red again. These results demonstrated that the single-component of Ca9Ln(PO4)7:Eu2+/3+ (Ln = Y, La) phosphor may be candidates for w-LED multi-color phosphors. •Ca9Ln(PO4)7: Eu2+/3+ phosphors with different Eu content were synthesized for the first time.•There are obvious differences in emission spectra between Ca9Y(PO4)7 and Ca9La(PO4)7 with the same structure β-Ca3(PO4)2.•Analysis of Eu2+ ions occupying different Ca2+ lattice sites in Ca9Y(PO4)7 and Ca9La(PO4)7 hosts by Gaussian fitted curves.