NaPbBi2(PO4)3: Ln3+ (Ln = Dy, Eu) Codoped Orthophosphate Type Phosphor for NUV Excitable WLEDs and Optical Thermometry

In this work a series of NaPbBi2(PO4)(3): 0.09Dy(3), xEu(3+) (NPbBP) phosphors were prepared. The phase formation and the morphological studies were analyzed using the PXRD data and SEM with EDS image respectively. The band gap value of the NPbBP (3.99 eV) and the NPbBP:0.09Dy(3+),0.09Eu(3+) (4.14 eV) samples were estimated from the DRS measurements. When exciting the NPbBP:0.09Dy(3+), xEu(3+) phosphors at 350, 364, 395 nm, the emission spectra exhibited peaks associated with transitions of both Dy3+ (F-4(9/2) -> H-6(J), J = 15/2, 13/2, 11/2, 9/2) and the Eu3+ ions (D-5(0) -> F-7(J), J = 0, 1,2 3). Both the Dexter theory and Reisfield's approximation were employed to investigate the energy transfer mechanism, revealing that dipole-dipole interactions are responsible for transferring the energy from Dy3+ to Eu3+ ions. By exciting at suitable wavelengths (350, 364 and 395 nm) in the NPbBP:0.09Dy(3+), xEu(3+) phosphors, the emission color could be tuned from neutral white (3769 K) to warm white (2630 K) to reddish orange light (1231 K). Further the luminescence decay curve measurements and emission spectra in the temperature range 303-483 K were specifically performed on the co-doped NPbBP:0.09Eu(3+),0.09Dy(3+) sample to inspect its temperature-dependent luminescence properties. At 423 K, the phosphor retains 65.5% of its initial value at room temperature. The analysis based on fluorescence intensity ratio (FIR) revealed that the phosphor had good relative sensitivity value of 0.65% K-1. These investigations collectively suggest that the co-doped phosphor holds significant promise for applications in phosphor converted LED and optical thermometry.