Synthesis and characterization of lithium barium diphosphate [Li2Ba3(P2O7)2] and Li2Ba3(P2O7)2:Cu2+ nanopowders

We synthesized lithium barium diphosphate [Li 2 Ba 3 (P 2 O 7 ) 2 ] and Cu 2+ -doped lithium barium diphosphate nanopowders using a novel wet-chemical method. X-ray diffraction was used to calculate the crystallite size, dislocation density, and micro-strain. Scanning electron microscopy revealed the surface characteristics of both nanopowder samples, while energy dispersive X-ray spectroscopy was used to study the qualitative and quantitative elements present in the synthesized samples. Vibrational modes of phosphates were studied using FT-IR and Raman spectroscopy. Optical absorption spectroscopy was used to determine direct and indirect bandgaps, which were found to be 4.55 eV and 4.08 eV, respectively, for the pure sample, whereas for the Cu 2+ -doped nanopowder, they were 4.03 eV and 3.84 eV, respectively. A single peak was observed at 825 nm in the optical spectrum. The Lande g-splitting factor was calculated using the EPR spectrum, and it was g ∥ = 2.3658, g ⊥ = 2.1109. The hyperfine splitting constant A was also calculated to be A ∥ = 128 X 10 − 4 and A ⊥ = 72 X 10 − 4 cm -1 . The photoluminescence of the pure sample exhibits bands at wavelengths of 415, 465, 514, 580, 600, and 619 nm, and the Cu 2+ -doped sample exhibits bands at wavelengths of 413, 438, 465, 513, and 618 nm. The excitation wavelengths of the PL spectra are approximately 321 and 324 nm, respectively, for the pure and Cu 2+ -doped nanopowders. The color coordinates of the pure host are located in the whitish-orange region, with CIE coordinates of x = 0.3551 and y = 0.3179, whereas the color coordinates for Cu 2+ -doped Li 2 Ba 3 (P 2 O 7 ) 2 show a yellowish-orange region with CIE coordinates of x = 0.4187 and y = 0.3593. The color characteristic parameters are calculated for both pure and Cu 2+ -doped samples. CRI and color fidelity index (R f ) values of the pure sample are 83% and 87%, respectively, whereas the Cu 2+ -doped sample shows CRI and R f values of 88% and 88%, respectively. Gamut factor (R g ) is a crucial parameter for fabricating light-emitting diodes, and the values of R g for the pure and Cu 2+ -doped samples are 111 and 110, respectively. These R g values confirm that light emitted by the prepared sample enhances the saturation of colors; i.e., it is more vibrant when compared to that from an ordinary light source.