A single-phased Ca4(PO4)2O: Tm3+, Tb3+, Eu2+ white light-emitting phosphor with tunable emission color

Abstract

The single-phased white light-emitting Ca4(PO4)2O: Tm3+, Tb3+, Eu2+ phosphors with tunable color emission were synthesized by solid-state reaction method. The photoluminescence properties, crystal structure, decay time and cross-relaxation from Tm3+ to Eu2+ were investigated in detail. Under excitation of 352 nm, Tm3+ singly doped Ca4(PO4)2O (denoted as TTCP) phosphors exhibited an intense emission peak at 458 nm attributed to 1D2 → 3F4 transition of Tm3+ ions and a broad emission peak in the range of 400–411 nm ascribed to oxygen vacancies in TTCP host. The emission intensity of oxygen vacancies decreases along with the increasing of Tm3+ doping concentration due to the substitution of Ca2+ and oxygen vacancies sites by Tm3+ ions. For Tm3+ and Eu2+ co-doped TTCP phosphors, the blue emission intensity (458 nm) of Tm3+ ions obviously decreased and the red emission intensity (624 nm) with of Eu2+ ions increased due to Eu2+ doping. The cross-relaxation from Tm3+ to Eu2+ ions was further demonstrated by the decay times of TTCP: 0.03 Tm3+, yEu2+ phosphors monitoring the emission peak at 458 nm. Further, Tb3+ ions were also introduced in the TTCP phosphor for a green emission and Tb3+ singly-doped TTCP phosphor displays the emission peaks at 488 nm and 545 nm due to the typical5D4→7F5 and 5D4→7F5 transition of Tb3+ ions, respectively. Finally, TTCP: Tm3+, Tb3+, Eu2+ phosphor was obtained and emitted the white light with the blue (458 nm), green (545 nm), and red (603 nm) emission bands under excitation of 352 nm. Especially, white light with tunable color temperature (3000 K–6000 K) and high color rendering index (Ra > 90) can be easily acquired. A neutral white light with high color rendering index (Ra 91.1) can be achieved for the TTCP: 0.03 Tm3+, 0.25 Tb3+, 0.004Eu2+ phosphor.