Cation‐ and Anion‐Substituted Potassium Manganese Phosphate, KMnP₃O₉: Luminescence and Photocatalytic Studies

Abstract

Phosphates as multifunctional materials were of vital importance in the environmental and energy fields. In the present work, a new cyclophosphate, potassium manganese phosphate (KMnP O ) (hereafter KMPO), was prepared by solid state method. Cations (Ag and Cu ) and anion (N ) were substituted into KMPO lattice via ion-exchange and solid state methods, respectively. The as-prepared materials were characterized by powder X-ray diffraction, SEM-EDS and UV-visible diffuse reflectance spectra. Rietveld refinement was carried out for parent material. All the prepared materials were found to crystallize in the hexagonal lattice and isomorphous with KCoP O . The nitrogen content in N -substituted KMPO was estimated by EDS and O-N-H analysis. The bandgap energy of the cation- and anion-substituted samples was lower compared to that of pristine KMPO. Gouy method was employed to determine the magnetic susceptibility of KMPO. The photoluminescence property of Mn in all the samples was studied, and the color coordinates were calculated using CIE 1931 chromaticity. The photocatalytic activity of visible light active material, N -substituted KMPO, was examined against the degradation of methylene blue and methyl violet at ambient conditions.

Structural and optical properties of Mg1−xMnxP2O6(x = 0–1.0) magnesium metaphosphate

“…Second, the distortion of MO 6 octahedron exerts the influences on band transition and optical absorption of Mg 1− x Mn x P 2 O 6 complete solid solution. Among transition metal ions, Mn 2+ has a very weak optical absorption due to the fact that all the d–d transitions in Mn 2+ are spin‐forbidden 24 . As shown in Figure 3B, the distortion rates (Δ) of (Mg/Mn)O 6 in Mg 1− x Mn x P 2 O 6 ( x = 0–0.5) are less distorted.…”

“…The 4 A 1g , 4 E g , 4 T 1g , 4 T 2g , 4 A 2g , 4 A 2g (F), and 4 T 1g (F) could be excited states. Therefore, Mn 2+ usually shows some spin‐forbidden absorption transitions from ground state 6 A 1g to quartet (or doublet) states 24 …”

“…Among transition metal ions, Mn 2+ has a very weak optical absorption due to the fact that all the d-d transitions in Mn 2+ are spinforbidden. 24 As shown in Figure 3B, the distortion rates (Δ) of (Mg/Mn)O 6 in Mg 1−x Mn x P 2 O 6 (x = 0-0.5) are less distorted. Therefore, the d-d transition probability is very small because of its weak distortion of the MnO 6 octahedral.…”

“…Therefore, Mn 2+ usually shows some spin-forbidden absorption transitions from ground state 6 A 1g to quartet (or doublet) states. 24 Compared with other transition metal ions, the optical absorption of Mn 2+ ions is often very weak because all dd transitions are Laporte forbidden. 24 Figure 5B shows the absorption in Mg 1−x Mn x P 2 O 6 (x = 0.6-1.0), which are distinct from those in the slightly distorted Mg 1−x Mn x P 2 O 6 (x = 0.1-0.5).…”

“…24 Compared with other transition metal ions, the optical absorption of Mn 2+ ions is often very weak because all dd transitions are Laporte forbidden. 24 Figure 5B shows the absorption in Mg 1−x Mn x P 2 O 6 (x = 0.6-1.0), which are distinct from those in the slightly distorted Mg 1−x Mn x P 2 O 6 (x = 0.1-0.5). With more Mn 2+ incorporated (x = 0.6-1.0), obvious excitation peaks at 420 and 365 nm were detected, which are originated from the d-d transitions in the octahedrally coordinated Mn 2+ ions.…”