•Y2MoO6:Eu3+ phosphors have been prepared by solid-state reaction and sol–gel technique.•Y2MoO6:Eu prepared using solid state method showed much stronger red emission under the n-UV excitation.•With a decrease of the crystalline size, the excitation bands of O–Mo CT shift to the short wavelength.•We can include that the origin of CT blue-shifts mainly came from the vacancies of O6 sites within the crystals through quantitative calculation based on the chemical bond viewpoint.Eu3+ activated micrometer Y2MoO6 phosphors with strong red emission bands, under a broad-band excitation wavelength range of 340–400 nm, have been prepared by solid-state reaction and sol–gel technique. The photoluminescence indicates that the materials exhibit a characteristic red emission peak of Eu3+ ions at 612 nm. Compared with the material obtained by sol–gel method, the Y2MoO6:Eu prepared using solid state method showed much stronger red emission under the n-UV excitation. The broad excitation bands are assigned to charge transfer (CT) bands originating from the ligands (O) to the central ions Mo6+. About 12 nm shift of excitation bands in Y2MoO6:Eu was found. With a decrease of the crystalline size, the excitation bands of O–Mo CT shift to the short wavelength. The origin of CT shift in macromaterial Y2MoO6:Eu was investigated quantitatively from the chemical bond viewpoint. All constituent chemical bonds in the crystal with or without oxygen vacancy were considered. The changes of average energy gap of the chemical bond Mo–O and the environmental factor (he) surrounding Mo6+ ions in the crystals were discussed quantitatively. Calculated results from two different methods analysis specifications showed that the origin of CT blue-shifts mainly come from the vacancies of O6 sites within the crystals.

•The composition of the product could be changed with different amount of EDTA.•The morphology of the product could be changed with different amount of EDTA.•The formation mechanisms and splitting patterns were put forward.In this paper, the YPO4:Eu3+ (5%) microflakes and YPO4·0.8H2O:Eu3+ (5%) microbundles have been synthesized by a simple EDTA-assisted hydrothermal method. The X-ray powder diffraction (XRD), thermogravimetric and differential thermal analysis (TG/DTA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and photoluminescence (PL) were employed to characterize the as-obtained products. It was found that the composition of the product could be changed from YPO4:Eu3+ (5%) to YPO4·0.8H2O:Eu3+ (5%) with a further increase in the amount of EDTA 0.5–1.0 g. The YPO4:Eu3+ (5%) presented the pure tetragonal phase and flake-like microstructure, while the YPO4·0.8H2O:Eu3+ (5%) exhibited the hexagonal phase and bundle-like morphology. The possible formation mechanisms of the two architectures were put forward on the basis of different EDTA amount-morphology experiments. A detailed investigation on the photoluminescence of YPO4·nH2O:Eu3+ (5%) different samples indicated that the luminescent properties of products were strongly dependent on the compositions, morphologies, coordination environment and crystal field symmetry.

Hexagonal GdBO3:Eu3+ with different morphologies, such as nanofibres, microspheres, microflowers and novel lotus leaf-like microstructures, have been successfully synthesized by complexing-agent-assisted hydrothermal process for the first time. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), energy-dispersive spectra (EDS), and photoluminescence (PL) spectroscopy were employed to characterize the as-obtained products. It was found that the reaction temperature and the pH value have crucial influences on the formation and morphology of the resulting structures and morphologies. The possible formation mechanisms for different structures were put forward. A detailed investigation on the photoluminescence of GdBO3:Eu3+ different samples indicate that the luminescence properties of as-obtained GdBO3:Eu3+ phosphors are strongly dependent on the morphology, size and crystallinity. The microflower structure exhibits the strongest red emission.Highlights► Novel structures GdBO3:Eu3+ have been synthesized by a hydrothermal process for first time. ► The effects of reaction temperature and pH value on the morphology of products have been studied. ► The formation mechanisms for different structures have been investigated in detail. ► The luminescence properties of GdBO3:Eu3+ with different morphologies have been studied in detail.

Eu(III) titanate nanotubes and nanowires have been successfully synthesized by solvothermal method using carbon nanotubes (CNTs) as removable templates. The products were characterized by X-ray diffraction spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry, thermogravimetric and differential thermal analysis. It is demonstrated that CNTs are fully coated with an amorphous Eu2(TiO3)3 layer, which is about 10 nm thick and almost continuous and uniform. After the Eu2(TiO3)3/CNTs composites have been calcined at various temperatures, Eu2(TiO3)3 nanotubes and nanowires are obtained by removing the CNTs templates. The diameter of the Eu2(TiO3)3 nanotubes is 40–60 nm, which is consistent with that of CNTs. Both nanotubes and nanowires have a narrow distribution of diameters. The fluorescence properties of the Eu2(TiO3)3 nanotubes and nanowires calcined at various temperatures have been investigated. The results indicate that when the Eu2(TiO3)3/CNTs composites were calcined at 700 °C for 5 h, the Eu2(TiO3)3 nanotubes obtained can be effectively excited by 395 nm light, and exhibit strong red emission around 616 nm. It is very interesting to discover that a few residual carbons doped in Eu2(TiO3)3 nanotubes and many oxygen vacancies could promote the intensity of red emission peak of Eu3+ ions. In addition, Eu2(TiO3)3 nanowires calcined at 900 °C for 5 h also have a strong red emission peak due to many oxygen vacancies and defects formed on the surface of the nanowires and inside them.

Large-scale GdBO3:Eu3+ nanofibres with uniform diameter were controllably synthesized by a glycine-assisted hydrothermal method at 170 °C using Gd(NO3)3, Eu(NO3)3 and Na2B4O7·10H2O as the precursors. X-ray diffraction (XRD) results show that the luminescent nanofibres are pure hexagonal structure and no other impurity phase appeared. Transmission electron microscopy (TEM) studies indicate that GdBO3:Eu3+ has a nanofibre structure. Photoluminescence (PL) spectra results demonstrate that the GdBO3:Eu3+ nanofibres have three strong 5D0 → 7F1 (595 nm) and 5D0 → 7F2 (613 and 627 nm) transition peaks corresponding to orange-red and red colors, respectively.

Eu(III) tungstates and molybdates nanotubes have been successfully synthesized by the solvothermal method using carbon nanotubes (CNTs) as removable templates. The products were characterized by X-ray diffraction spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry, thermogravimetric and differential thermalanalysis. It is demonstrated that CNTs are fully coated with an amorphous Eu2(MO4)3 (M = W, Mo) layer, which is about 10 nm thick and almost continuous and uniform. After the Eu2(MO4)3 (M = W, Mo)/CNTs composites have been calcined at 700 °C, Eu2(MO4)3 (M = W, Mo) nanotubes are obtained by removing the CNTs templates. The diameter of the Eu2(MO4)3 (M = W, Mo) nanotubes is 40–60 nm, which is consistent with that of CNTs. The luminescence properties of the Eu2(MO4)3 (M = W, Mo) nanotubes calcined at various temperatures have been investigated. The result shows that the Eu2(MO4)3 (M = W, Mo) nanotubes obtained from the Eu2(MO4)3 (M = W, Mo)/CNTs composites calcined at 700 °C display a strong red emission peak at around 611 nm.