La2(MoO4)3 phosphors with various Eu3+ concentrations were prepared via a facile co-precipitation process. The crystal structure and morphology of the phosphors were characterized by means of XRD and field emission scanning electron microscope. The crystal unit cell parameters a, b, and c for the monoclinic phase La2(MoO4)3 were calculated to be 16.989, 11.927, and 16.086 Å, respectively. The average size of the phosphor particles was estimated to be around 88.5 nm. The Huang–Rhys factor was derived from the phonon sideband spectra to be 0.073. The self-generated quenching process of Eu3+ was explained based on Auzel’s model, and the intrinsic radiative transition lifetime for 5D0 level was confirmed to be 0.99 ms. A new approach for calculating the Judd–Ofelt parameters was developed, meanwhile the Judd–Ofelt parameters Ωλ (λ = 2, 4, 6) of Eu3+ in La2(MoO4)3 phosphors were confirmed to be 10.70 × 10−20, 1.07 × 10−20, and 0.56 × 10−20 cm2, respectively. Finally, the optimal doping concentration for achieving maximum emission intensity was confirmed to be 17 mol. % by analyzing the concentration quenching.
Ln 3+ doped (Yb 3+ ,Tm 3+ codoped and Yb 3+ ,Er 3+ ,Tm 3+ tridoped) NaYF 4 /poly(vinyl pyrrolidone)(PVP) (M w ≈ 1 300 000) composite fibers with an average diameter of 300-800 nm were prepared by electrospinning and characterized by X-ray diffraction, field emission scanning electron micrography, and Fourier transform infrared spectra. Their upconversion (UC) luminescence properties were studied in contrast to the corresponding Ln 3+ doped NaYF 4 nanoparticles (15-20 nm) under 980-nm excitation. The results demonstrate that in the Yb 3+ ,Tm 3+ codoped composite fibers the blue emission of 1 G 4 -3 H 6 is dominantly strong, while in the nanoparticles the red emission of 3 F 2,3 -3 H 6 contributes considerably to the increase of the excitation power. This indicates that the color purity of blue is improved greatly by the modification of PVP. In the tridoped Yb 3+ ,Er 3+ ,Tm 3+ composite fibers, white light with more stable color balance (blue 1 G 4 -3 H 6 of Tm 3+ , green 2 H 11/2 / 4 S 3/2 -4 I 15/2 , and red 4 F 9/2 -4 I 15/2 of Er 3+ ) was obtained. The improved UC properties in the composite fibers are attributed to the suppressed local thermal effect. The energy transfer and UC populating processes are discussed.
A novel method, electrospinning, was explored to prepare europium-doped YBO3 nanocrystalline phosphors. Narrow and size-controllable YBO3 nanotubes and nanowires were obtained, varying from 40 to 500 nm. The average wall thickness of the nanotubes was only 5−10 nm. The structural properties were characterized by X-ray diffraction (XRD), Fourier-transform infrared absorption (FTIR), electron spin resonance (ESR), field emission scanning electron micrographs (FE-SEM), and high-resolution transmission electron micrographs (HR-TEM). The results indicate that theYBO3 nanotubes and nanowires were hexangular in phase and single crystals or polycrystalline in structure. Some surface dangling bonds caused by transition metal ions lead to a change of the coordination number of boron from +3 to +4. The photoluminescent properties of the YBO3: Eu3+ nanowires and nanotubes were also characterized. It was observed that the charge-transfer excitation bands of Eu3+ in the nanowires and nanotubes blue-shifted in contrast to those in bulk, because of the variation of coordination environments.
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