This tutorial review focuses on the recent development of diverse synthetic approaches and possibilities for chemical tuning of the size, shape, and morphology, as well as properties such as luminescence, of rare earth tungstate and molybdate materials. The use of rare earth tungstate and molybdate nano- and micromaterials as single materials for the generation of white light is reviewed. Additionally, the use of these materials as red phosphors in phosphor-converted white light emitting diodes (pc-WLEDs) when employing GaN or InGaN chips as the primary light source is explored.

Rare earth tungstate and molybdate compounds – from 0D to 3D architectures

Triple molybdate NaCaLa(1−x−y)(MoO4)3:xEr3+,yYb3+ (x = y = 0, x = 0.05 and y = 0.45, x = 0.1 and y = 0.2, x = 0.2 and y = 0) phosphors were successfully synthesized for the first time by the microwave sol–gel method. Well-crystallized particles formed after heat treatment at 900 °C for 16 h showed a fine and homogeneous morphology with particle sizes of 2–3 μm. The structures were refined by the Rietveld method in the space group I41/a. The optical properties were examined comparatively using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the NaCaLa0.7(MoO4)3:0.1Er3+,0.2Yb3+ and NaCaLa0.5(MoO4)3:0.05Er3+,0.45Yb3+ particles exhibited a strong 525 nm emission band, a weaker 550 nm emission band in the green region, and three weak 655 nm, 490 nm and 410 nm emission bands in the red, blue and violet regions. The pump power dependence and Commission Internationale de L'Eclairage chromaticity of the upconversion emission intensity were evaluated in detail.

/pdf/triple-molybdate-scheelite-type-upconversion-phosphor-nacala-1e7nv3lqfv.pdf

Triple molybdate scheelite-type upconversion phosphor NaCaLa(MoO4)3:Er3+/Yb3+: structural and spectroscopic properties.

Nanocrystalline REF3:Tb3+ fluorides (where RE = Y, La, Ce, Gd, and Yb) have been synthesized using a precipitation method in a water/glycerine system. Glycerine, which was added in 25% by volume to Ln(NO3)3 and NH4F reactant solutions, prevented an uncontrolled growth of the nanocrystals and enhanced the stability of the colloids formed in water. X-ray analysis and transmission electron microscopy confirmed the formation of the fluoride nanocrystals. Additionally, the presence of glycerine on the surface of the crystallites was established on the basis of IR measurements. The use of Tb3+ ions resulted in a green luminescence of the products, with a maximum of this emission at 545 nm. Spectroscopic analysis was performed to investigate the effects of the fluoride matrix on the luminescent properties of the Tb3+ ions. Quantum yields were also determined. In particular, the most efficient system, based on CeF3 doped with 15% Tb3+, was investigated in detail.

Influence of Matrix on the Luminescent and Structural Properties of Glycerine-Capped, Tb3+-Doped Fluoride Nanocrystals

Different types of titanate and titania nanostructured materials have been successfully synthesised and characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and raman spectroscopy. Elemental analysis was determined by energy dispersive X-ray spectroscopy (EDX) analyzer while thermogravimetric-differential scanning calorimetry (TG-DSC) was used to determine thermal stability. In this study, we found that nanotubes were formed during the washing treatment stage with HCl and distilled water. When the pH of the washing solution was 12, sodium titanate nanotubes were obtained, while when the pH of the washing solution was 7, hydrogen titanate nanotubes were obtained. Sodium titanate nanotubes were thermally stable up to 500°C; however, at 700°C, the nanotubes structure transform to solid nanorods. Meanwhile, hydrogen titanate nanotubes decomposed to produce titania nanotubes after heat treatment at 300°C for 2 hours. At 500°C, the tubular structure broke to small segments due to destruction of the nanotube. Further heat treatment at 700°C, led to the destruction and collapse of the nanotubes structure produce titania nanoparticles.

/pdf/morphological-and-structural-studies-of-titanate-and-titania-4zj3ronq3k.pdf

Morphological and structural studies of titanate and titania nanostructured materials obtained after heat treatments of hydrothermally produced layered titanate

A series of scheelite-type Eu3+-activated CaMoO4 phosphors were synthesized by the nitrate-citrate gel combustion method. All the compounds crystallized in the tetragonal structure with space group I4(1)/a (No. 88). FESEM results reveal the spherical-like morphology. The CaMoO4 phosphor exhibited broad emission centered at 500 nm under the excitation of 298 nm wavelength, while Eu3+-activated CaMoO4 shows an intense characteristic red emission peak at 615 nm at different excitation wavelengths, due to D-5(0) -> F-7(2) transition of Eu3+ ions. The intensities of transitions between different J levels depend on the symmetry of the local environment of Eu3+ ions and were estimated using the Judd-Ofelt analysis. The high asymmetric ratio revealed that Eu3+ occupies sites with a low symmetry and without an inversion center. The CIE chromaticity co-ordinates (x, y) were calculated from emission spectra, and the values were close to the NTSC standard. Therefore, the present phosphor is highly useful for LEDs applications.

Photoluminescence properties of Eu3+-activated CaMoO4 phosphors for WLEDs applications and its Judd-Ofelt analysis

Self-assembled 3D flower-like NaY(MoO4)2:Eu3+ microarchitectures: Hydrothermal synthesis, formation mechanism and luminescence properties

Hydrothermal synthesis of YBO3:Tb3+ microflowers and their luminescence properties

Controlled synthesis of different morphologies of GdBO3:Eu3+ crystals and shape-dependent luminescence properties

The Eu3+‐doped La2Zr2O7phosphor with rod‐like morphology was successfully synthesized by conventional solid state reaction and hydrothermal method. X‐ray diffraction patterns, transmission electron microscopy, and photoluminescence spectra were employed to characterize its structure and morphology as well as luminescent properties. The results indicated that the red‐emitting phosphor La2Zr2O7:Eu3+ had well crystallized and belonged to the cubic structure with space group of Fd3m. The as‐obtained product mainly appeared as straight nanorods with an average diameter of 47 nm and length of 50–700 nm. The possible growth mechanism was also discussed. It was found that under blue excitation with a wavelength of 466 nm, the La2Zr2O7:Eu3+ phosphor exhibited a characteristic red emission at 616 nm that was attributed to the hypersensitive 5D0→7F2electric dipole transition of Eu3+ ions. Meanwhile, it was more interesting to note that the emission of 5D1→7FJ (J=0, 1, 2) transitions and the splitting patterns of 5D0...

Synthesis, Characterization and Luminescent Properties of La2Zr2O7:Eu3+ Nanorods

A study on the structure transformation and luminescence of Eu(III) titanate nanotubes synthesized at various hydrothermal temperatures

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