A novel precursor route for Y2Mo4O15:Yb3+,Ho3+ phosphor and investigation of up-conversion luminescence

Development of SrWO4:Ho3+/Yb3+ green phosphor for optical thermometry application

In recent years, the growth of luminescent materials for optical thermometry applications has gained substantial attention due to their non-invasive and contactless nature. This research article presents the synthesis, characterization, and potential application of SrWO4:Ho3+/Yb3+ phosphors as temperature-sensitive materials. The inspection of the structural properties is done by X-ray diffraction and Raman and FTIR spectroscopy. The X-ray diffraction signifies the single tetragonal phase of the materials without any impurity or secondary phase. Nine Raman active modes are detected in the Raman spectra of pure SrWO4 and 10 Raman active bands are present in the doped samples. The morphology and elemental composition are visualised by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) spectroscopy. The spectral properties of these phosphors are evaluated by down-conversion and up-conversion photoluminescence, signifying their suitability for solid state lighting and optical thermometry in various temperature regimes. The phosphors can generate green and yellow light under blue and near-infrared radiation, respectively. The sensitivity of 3.19 × 10-3 K-1 ensures the promising prospects of SrWO4:Ho3+/Yb3+ phosphors for precise and reliable temperature sensing in diverse fields.

Systematic Crystallization of NH4Ln(MoO4)2 as a Family of Layered Compounds (Ln = La-Lu and Y), Derivation of Ln2Mo4O15, Crystal Structure, and Photoluminescence

NH₄Ln(MoO₄)₂ (Ln = La-Lu lanthanide, Y) was crystallized via hydrothermal reaction as a new family of layered materials, from which phase-pure Ln₂Mo₄O₁₅ was successfully derived via subsequent annealing at 700 °C for the series of Ln elements excluding Ce and Lu. Detailed structure analysis revealed that the ionic size of Ln³⁺ decisively determined the crystal structure and Mo/Ln coordination for the two families of compounds. NH₄Ln(MoO₄)₂ was analyzed to be orthorhombic (Pbcn space group, no. 60) and monoclinic (P2/c, no. 13) for the larger and smaller Ln³⁺ of Ln = La-Gd and Ln = Tb-Lu (including Y), respectively, where both the crystal structures have a layered topology featured by the alternative stacking of a [Ln(MoO₄)₂]^- three-tier infinite anionic layer and interlayer NH₄⁺. Four types of crystal structures were found for the Ln₂Mo₄O₁₅ series, which are monoclinic (P2₁/a, no. 14) for Ln = La, triclinic (P1̅, no. 2) for Ln = Pr-Sm, triclinic (P1̅, no. 2) for Ln = Eu and Gd, and monoclinic (P2₁/c, no. 14) for Ln = Tb-Yb (including Y). The photoluminescence of NH₄Ln(MoO₄)₂ (Ln = Eu, Tb) and Ln₂Mo₄O₁₅:Eu³⁺ (Ln = La, Gd, Y) was thoroughly investigated in terms of spectral features, quantum efficiency, fluorescence decay, and CIE chromaticity. The thermal stability of luminescence was also studied for Ln₂Mo₄O₁₅:Eu³⁺, and the observed charge-transfer excitation components were successfully correlated with the features of the Mo-O polyhedron/unit.

Extensive tailoring of REPO4 and REVO4 crystallites via solution processing and luminescence

This article highlighted the recent achievements in crystal engineering of REPO4 and REVO4via solution processing, with an emphasis on solution chemistry, the role of chelate ion, crystallization mechanism and luminescence properties.