Structural, morphological and photoluminescence studies of Ca7Mg2P6O24:RE3+(RE3+= Tb3+, Dy3+) nanophosphor for solid state illumination

The Ca₇Mg₂P₆O₂₄:RE³⁺ (RE³⁺= Tb³⁺, Dy³⁺) nanophosphor material was synthesized by traditional wet chemical method. The XRD are used to determine phase and crystallinity of the synthesized sample; further FTIR, SEM, TEM, and PL properties were studied. The XRD pattern of prepared sample match well with standard JCPDS card no 00–020–0348, and it exhibits the rhombohedral structure along with space group R3c (161). The phosphate (PO₄)^3-group absorption band was observed at 990–1100 cm^-1 in FTIR. Surface morphology (TEM analysis) reveals particle sizes in the range of 55–110 nm. The luminescence emission spectra of Ca₇Mg₂P₆O₂₄ phosphor activated by Tb³⁺ were studied at three different excitations: 352 nm, 370 nm, and 379 nm. The spectra show two emission peaks at 470 nm (blue) and 545 nm (green). These are due to the ⁵D₄ → ⁷F₆ and ⁵D₄ → ⁷F₅ transitions of Tb³⁺ ions. The highest intensity peak is located at 545 nm. The Ca₇Mg₂P₆O₂₄:Tb³⁺ phosphor's CIE chromaticity coordinates are (0.040, 0.316) at 491 nm and (0.265, 0.724) at 543 nm. These are in the blue and green areas on the edges of the CIE diagram, respectively. The photoluminescence emission spectra of Dy³⁺-doped Ca₇Mg₂P₆O₂₄ phosphor show two significant emission peaks located at 482 nm and 574 nm. These are caused by the ⁴F_9/2 → ⁵H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions of Dy³⁺ ions, which produce blue and yellow light, respectively, with an excitation wavelength of 350 nm. The sharp peak position at 482 nm produces the strongest emission. The effect of concentration quenching in between the Dy³⁺-Dy³⁺ions and Tb³⁺-Tb³⁺ ions is due to dipole-dipole interaction. The CIE color coordinate is found to be (0.082, 0.156) at 482 nm and (0.471, 0.527) at 574 nm which lies in blue and yellow border of CIE diagram. The lifespan of Tb³⁺, Dy³⁺activated Ca₇Mg₂P₆O₂₄ nanophosphor of highest concentration is found to be 1.917 ms and 0.9985 ms respectively. On investigation, the synthesized Tb³⁺, Dy³⁺activated Ca₇Mg₂P₆O₂₄ nanophosphor can be potential for solid lightning devices & other display application.