Existence of Surface Bi 3+ and Energy Transfer in YP x V 1– x O 4 :Bi 3+ Nanocrystals

This study reports the systematic study of the solid–solid solution of YPxV1–xO4:Bi3+ (1 at. %) (0 ≤ x ≤ 1) prepared by the hydrothermal method. Polyvinylpyrrolidone (PVP) was used as a capping agent. The crystallization of YPxV1–xO4:Bi3+ in the tetragonal zircon-type structure is revealed after careful analysis using X-ray diffraction with Rietveld refinement. FT-IR supports the solid–solid formation of YPxV1–xO4. The transmission electron microscopy (TEM) image shows spindle-shaped particles and corroborates the correct crystalline formation. The substitution of V5+ lattice sites by the P5+ is evident from the gradual shifting of diffraction planes toward a higher angle and decreasing interplanar spacing from SAED. Steady-state photoluminescence (PL) and decay lifetime studies of YP0.7V0.3O4:yBi3+ reveal the occurrence of efficient energy transfer (ET) from VO43– (donor/sensitizer) to Bi3+ (activator). The PL excitation spectra show the presence of three different types of excitation states, viz., (i) the O-2p states to the V-3d states in VO43–, (ii) the Bi-6s states to V-3d, called metal-to-metal charge transfer (MMCT), and (iii) Bi-6s → Bi-6p. This is supported by the DFT calculation. The MMCT bands observed are well matched with the theoretical calculation using the Philippe Boutinaud equation. Along with the lattice substitution of Y3+ sites by Bi3+, the presence of Bi3+ on the surface of the nanoparticle is also seen. The tuning of emission color from green to greenish-blue with the increasing x is evident from the Commission International del’ Eclairage (CIE) chromaticity coordinates. This can be a potential phosphor candidate for white light-emitting diodes.