Study on luminescent properties of orange phosphor NaCaPO₄ :Eu³

The NaCaPO₄ :Eu³⁺ phosphor was synthesized by the sol-gel method. The structure and luminescence properties of the phosphor were analyzed by thermogravimetric-differential thermal analysis (TG-DTA), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and fluorescence spectroscopy. TG-DTA results show that NaCaPO₄ phase can be formed after 700°C. FTIR spectra confirmed the existence of PO₄ units. XRD results show that the sample is a pure NaCaPO₄ orthorhombic crystal phase. The TEM diagram shows that the sample has good uniformity. The NaCaPO₄ :Eu³⁺ emits orange light under 394 nm excitation. The optimal doping concentration is 3 mol%. The reason for concentration quenching is caused by multipolar interaction. Through further analysis of the charge transfer band and the spectrum at ⁵ D₀  → ⁷ F₀ transition of the NaCaPO₄ :Eu³⁺ phosphor, the reason for the orange light of the phosphor is owing to the different Eu³⁺ occupancy which is explained in detail.