Cool White Light Emitting Dy³⁺ Activated Disodium Calcium Pyrophosphate Phosphor for WLEDs Application

A series of Na₂CaP₂O₇: xDy³⁺ (x = 0.01-0.06) (abbreviated as NCPO) phosphors were synthesized using the solid-state reaction method in the present research work. X-ray diffraction (XRD) was used to confirm the phase purity and crystallinity of the synthesized phosphors. Morphological and elemental analyses were carried out using field emission scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDS), respectively. Fourier transform infrared (FT-IR) spectroscopy assessed the functional groups, while diffuse reflectance spectroscopy (DRS) was employed to estimate the optical band gap. Photoluminescence (PL) spectroscopy was performed at an excitation wavelength of 351 nm to investigate the luminescence properties of the prepared phosphors. Two emission bands were subsequently observed at 485 nm and 575 nm, corresponding to ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions, respectively. The critical distance (R_c) between Dy³⁺ ions in this host was calculated to be 17 Å, indicating that both nearest-neighbor ion interactions and dipole-dipole interactions were involved. The PL decay lifetime and internal quantum efficiency (IQE) of the synthesized phosphor are determined. Photometric studies reveal that the CIE coordinates fall very close to the white light region, and the CCT value is found to be greater than 5000 K, indicating that the prepared NCPO: Dy³⁺ phosphor is a promising candidate for cool WLEDs for outdoor lighting applications.