Synthesis and luminescent features of NaCaPO4:Tb3+ green phosphor for near UV-based LEDs

Highlights: ► Successfully synthesized orthorhombic phase of NaCaPO4 (NCP) phosphors ► Structural and Luminescent properties have been investigated. ► In the excitation spectrum, 7F6→5G6 transition at 370 nm exhibit highest intensity. ► CIE coordinates of Tb3+: NCP phosphor indicate green light emission in CIE diagram. ► Hence, Tb3+ doped NaCaPO4 is suitable for UV based pc-LEDs. -- Abstract: An efficient green emitting Tb3+ doped NaCaPO4 (NCP) phosphor was synthesized by using conventional solid-state reaction for solid-state lighting applications. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), FT-IR, emission and excitation properties were extensively investigated for NCP phosphors. X-ray diffraction analysis confirmed the formation of NaCaPO4 with orthorhombic structure. The excitation spectrum consists of strong 4f–4f transition at around 370 nm, which has higher intensity than the f–d transition. Emission spectra indicated that this phosphor can be efficiently excited by UV light in the range from 250 to 400 nm, and shows strong emission band centered at 547 nm. Analysis of the emission spectra with different Tb3+ concentrations revealed that the optimum dopant concentration for these NCP phosphors is about 5 mol% of Tb3+. Diminishing of 5D3 level and increasing of 5D4 level emission intensity with the Tb3+ concentration explained successfully. The emission color was analyzed and confirmed with the help of chromaticity coordinates and color temperature. The excellent luminescent properties of NaCaPO4:Tb3+ phosphor makes it as a potential green phosphor upon near-UV LED excitation