Synthesis, Structure, Morphology, and Photoluminescence in GdNb2VO9:Sm3+ Phosphor for Optical Applications

Abstract

A series of an orange-red-emitting phosphor, GdNb₂VO₉:Sm³⁺, was synthesized using the solid-state reaction route. For the structural analysis, the synthesized samples were analysed using x-ray diffraction (XRD). From the analysis, it was found that the sample has a perovskite-like structure. To study the morphology of the synthesized samples and for elemental mapping, scanning electron microscopy (SEM) coupled with energy-dispersive x-ray spectroscopy (EDS) was used. SEM confirmed that the particles differed in size and shape. Using EDS, it was confirmed that Gd, Nb, V, and O were present in the desired ratio in the sample. The photoluminescence properties and decay kinetics were investigated to evaluate its potential for solid-state lighting applications. The excitation spectrum was monitored at 605 nm and is dominated by a broad and intense host charge transfer band (CTB) centred at 312 nm. This originates from the vanadate (VO₄)³⁻ and niobate (NbO₄)³⁻ groups. Upon excitation at 312 nm, the phosphor exhibits 4f → 4f transitions which are characteristic transitions of Sm³⁺, with the most prominent emission peak located at 605 nm (⁴G_5/2 → ⁶H_7/2). The dominance of the host-related band over the direct Sm³⁺ transitions indicates an efficient energy transfer process from the GdNb₂VO₉ host lattice of the activator ions. The luminescence decay curve of the ⁴G_5/2 level follows mono-exponential behaviour with a calculated lifetime of 0.664 ms, suggesting a uniform distribution of Sm³⁺ in the host matrix. Also, the calculated CIE 1931 chromaticity coordinates confirm high colour purity in the orange-red region. Concentration quenching was observed for the 7 mol.% Sm³⁺-doped sample, which is because of non-radiative energy migration between Sm³⁺ ions, cross relaxation processes, and multipolar interaction, likely dipole–dipole type. Furthermore, the high colour purity under 407 nm excitation indicates that the emission is strongly dominated by the characteristic orange-red transitions of Sm³⁺ ions, demonstrating the effectiveness of Sm³⁺ incorporation in tuning the emission colour of the host lattice. In this study, time decay characteristics were studied in detail. The estimated value of quantum efficiency was found to be of the order of 74.8% to 78.8%. These results demonstrate that GdNb₂VO₉:Sm³⁺ is a suitable candidate as a red-emitting component for near-UV-excited white light-emitting diodes (w-LEDs).

Graphical Abstract