Dandan Ju

Effect of the focal shaping generated from different double-mode cylindrical vector beams

We investigate three-dimensional focus shaping generated from double-mode cylindrical vector beams with the Gaussian and Bessel-Gaussian pupil apodization functions by choosing the suitable polarization states of beams. Further, we compare them with that generated from the Laguerre-Gaussian pupil apodization function in the same situation. We find that the focus shaping generated from the Gaussian beam has the smallest zero intensity spot size. However, the situation of the Bessel-Gaussian beam not only possesses stability, which makes it suitable when applied in optical trapping, but also shows the best uniformity, which indicates its excellent performance in super-resolution fluorescence microscopy.

Simultaneous size adjustment and upconversion luminescence enhancement of β-NaLuF4:Yb3+/Er3+,Er3+/Tm3+ microcrystals by introducing Ca2+ for temperature sensing

β-NaLuF4:Yb3+/Er3+ microcrystals have been obtained through a facile hydrothermal method at a relatively low temperature (180 °C) within only two hours. By introducing Ca2+ ions, the microcrystals can simultaneously be tunable in size and realize upconversion luminescence enhancement. It is found that when the concentration of Ca2+ ions increases from 0 to 20 mol%, the average diameter of disks increases while the height decreases. However, with the concentration of Ca2+ further increasing, the opposite is true. This result can be ascribed to the capping effect of F− on the different crystal faces. More importantly, the upconversion luminescence intensities of green and red emissions of β-NaLuF4:Yb3+/Er3+ with 40 mol% Ca2+ ion doping are about 7.5 and 7.9 times higher than those of the sample without Ca2+ doping, respectively. Besides, the Ca2+ doping can also be extended to β-NaLuF4:Er3+/Tm3+ for enhancement of the upconversion luminescence. Eventually, emphasis will be on the temperature-dependent upconversion properties of β-NaLuF4:20Yb3+/2Er3+/40Ca2+ (mol%) and Ca2+-free samples. The maximum sensitivity of β-NaLuF4:20Yb3+/2Er3+/40Ca2+ (mol%) (0.00040 K−1) is higher than that of β-NaLuF4:20Yb3+/2Er3+ (mol%) (0.00021 K−1) at 120 K under the same excitation pump power of 1 W, indicating that the sample with Ca2+ has potential for application to temperature sensing.

Spatially confined luminescence process in tip-modified heterogeneous-structured microrods for high-level anti-counterfeiting

Recent years have witnessed the progress of lanthanide-doped materials from fundamental material synthesis to targeted practical applications such as optical applications in photodetection, anti-counterfeiting, volumetric display, optical communication, as well as biological imaging. The unique compositions and structures of well-designed lanthanide ion-doped materials could expand and strengthen their application performances. Herein, we report dual-mode luminescent crystalline microrods that spatially confine upconversion and downconversion photophysical process within defined regions using the specially designed heterogeneous structure. Through an epitaxial growth procedure, downconversion tips have been conjugated with the parent upconversion microrods in oriented directions. This spatially confined structure can effectively depress the deleterious energy depletion in lanthanide ions homogeneously doped materials, and as a result, the red, green, and blue upconversion intensities have been enhanced by 334, 225, and 22 times, respectively. Moreover, the induced tips hardly disturb the upconversion process of the microrod seeds. Upon 980 nm laser or ultraviolet lamp excitation, tunable emission colors were realized in the single tip-modified microrod, indicating potential applications of these microrods for high-level dual-mode anti-counterfeiting.

Sequential Growth of Uniform β-NaYF4@β-NaLnF4 (Ln = Y, Lu, Yb) Microcrystals with Luminescent Properties of Multicolor Tuning and Dual-Mode Emission

We synthesized the uniform core-shell microstructured compounds with hexagonal phase NaYF4:Er/Yb microrods as the core and hexagonal phase NaLnF4 (NaYbF4, NaLuF4:Yb/Tm, NaYF4:Yb/Er, NaYF4:Eu) as the shell based on the hydrothermal reaction. These microscale core-shell structures provided a platform for the spatially confining optical process while possessing high luminescence efficiency. The thickness of the shell could be controlled by adjusting the amounts of shell precursor, which significantly affected the intensity of the shell dopant ions emission and the emission color of core-shell upconversion luminescence (UCL). The uniform NaYF4@NaLnF4 (Ln = Y, Lu, Yb) microrods, with a series of rare-earth ions doped into the core and shell layer at various doping concentrations, achieved color-tuning of the upconversion (UC) emission and dual-mode emission at the single-microcrystal level, thus allowing the efficient utilization of core-shell microcrystals in the photonics and security labeling. This study suggests a new class of luminescent materials in the microscopic field.

Trapping metallic particles under resonant wavelength with 4π tight focusing of radially polarized beam.

Here we propose a new method for trapping the resonant metallic particles with the 4π tight focusing (high numerical-aperture (NA)) system, which is illuminated by radial polarization light. Numerical simulations have indicated the maximum total optical force is 16.1pN while with nearly zero scattering force under axis trapping, which keeps the gradient force predominant. Furthermore, the distribution of total force is centrosymmetric and odd. We also gain stable 3D trap with an equilibrium point along z axis and r axis as in normal optical tweezers. Whats more, we obtain the nearly pure longitudinal field. The maximum transverse intensity is only 2.3 × 10-3 and the transverse spot size reaches 0.36λ, which is below Abbes diffraction limit.