Remarkable influence of alkaline earth ions on the enhancement of fluorescence from Eu³⁺ ion doped in sodium ortho-phosphate phosphors

A series of different alkaline earth based sodium-ortho phosphate (NaMPO₄, where M = Mg, Ca, Sr and Ba) phosphors doped with 1 mol% of Europium (Eu³⁺) were prepared by solution combustion method. The phase evolution controlled morphology and fluorescence properties were systematically examined by various techniques such as X-Ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopy. Our materials crystallized into monoclinic and orthorhombic phases that were found to be consistent with those listed in the standard JCPDS cards. The XRD results confirmed that the samples contained a mixture of phases in the crystals. The PLE spectra of the NaMPO₄ phosphors consisted of a broad band with a maximum at 278 nm, while the Eu³⁺ doped phosphors contained a similar broad band of lower intensity and characteristic Eu³⁺excitation bands. These phosphors could be efficiently excited by near ultraviolet at 393 nm and were found to exhibit excellent red emission at 593 nm corresponding to the ⁵D₀→⁷F₄ transition of the Eu³⁺ ion. The calculated Commission Internationale de l'Eclairge (CIE) chromaticity color coordinates were calculated. The color of the emitting light could be tuned from orange-red to red through incorporation of different alkaline metal ions. All the results suggested that the examined sodium-ortho phosphates could potentially be used as sources of red light in tricolor white light emitting diodes.