Multifaceted insight into the cation-disordered self-activated luminescence of Zn3V2O8 compositions for lighting and pigment applications

Abstract

Orthovanadates are featured with the remarkable advantages of structural diversity-dependent photoluminescence due to ligand-to-metal VO₄³⁻ charge transfer luminescence. Among them, the self-activated Zn₃V₂O₈ composition possesses unique structural frameworks compared to other orthovanadates due to the linking of Zn²⁺ 3d orbitals with O²⁻ 2p orbitals in the valence band. The same O²⁻ 2p orbitals are again connected with V⁵⁺ 3d orbitals in the conduction band via the formation of the O²⁻–V⁵⁺ charge transfer band. Such diversity is responsible for the higher luminescence efficiency of this self-activated host. In this study, the structure of Zn₃V₂O₈ was further modified through several cationic substitutions (In³⁺, Y³⁺, Bi³⁺, and K⁺) to induce charge variation and distortion in VO₄³⁻ clusters and consequently enhance its luminescence behaviour. All the cation-substituted Zn₃V₂O₈ phosphors were crystallized in an orthorhombic structure with a cmca-64 space group. The compositions with optimized concentrations of (In³⁺, Y³⁺, Bi³⁺, and K⁺) cations showed a higher luminescence than the host in the greenish-yellow region due to the variation in V–O bond lengths with internal quantum efficiencies of 54.1%, 69.4%, 67.4%, and 51.8%, respectively. The optimized Y³⁺ ion incorporated Zn₃V₂O₈ sample showed a decent photoluminescence (PL) stability of 51% at 448 K compared to the room temperature PL intensity with an activation energy of 0.25 eV. A white light-emitting diode (W-LED) was fabricated by combining the above sample with the blue-emitting BaMgAl₁₀O₁₇: Eu²⁺ (BAM: Eu²⁺) phosphor and a 365 nm near-UV-LED chip. The resultant correlated color temperature (CCT) of 4662 K and color rendering index (CRI) of 84 of the fabricated W-LED could be suitable for indoor lighting applications. Meanwhile, the optimized Bi³⁺ and K⁺ ion-incorporated samples exhibited excellent yellow (a* = 4.84, b* =62) and orange colors (a* = 33.99, b* = 40.86), respectively, due to the synchronized absorption bands of O²⁻–V⁵⁺. The above yellow and orange samples showed exceptional near-IR reflectance, estimated to be 87% and 85%, respectively. For the first time, the present research promoted the multifunctional features of self-activated Zn₃V₂O₈ compositions through cation substitution-induced distortions in the surrounding VO₄³⁻ tetrahedral sites, which ensured their potential in lighting and pigment applications.