Existence of Surface Bi ³⁺ and Energy Transfer in YP _<i>x</i> V _{1– <i>x</i>} O ₄ :Bi ³⁺ Nanocrystals

This study reports the systematic study of the solid–solid solution of YP x V 1– x O 4:Bi 3+ (1 at. %) (0 ≤ x ≤ 1) prepared by the hydrothermal method. Polyvinylpyrrolidone (PVP) was used as a capping agent. The crystallization of YP x V 1– x O 4:Bi 3+ 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 YP x V 1– x O 4 . The transmission electron microscopy (TEM) image shows spindle-shaped particles and corroborates the correct crystalline formation. The substitution of V 5+ lattice sites by the P 5+ 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 YP 0.7 V 0.3 O 4:yBi 3+ reveal the occurrence of efficient energy transfer (ET) from VO 4 3– (donor/sensitizer) to Bi 3+ (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 VO 4 3–, (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 Y 3+ sites by Bi 3+, the presence of Bi 3+ 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.