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Nd3+-Sensitised luminescent upconversion nanoparticles (UCNPs) have gained interest recently as theranostics due to their near-infrared (NIR) light excitation with a better tissue penetration depth. One example is the core/shell design NaYF4:Yb,Er@Nd,Yb. When harvesting the upconversion energy in such architectures, the long emitter-photosensitizer (i.e. Er3+-PS) distances lead to inefficient Förster resonance energy transfer (FRET). Herein, we report a new nanocomposite NaYF4:Nd,Yb@Yb@Yb,Er@Y with Nd3+ ions in the core and Er3+ ions in the shell to shorten the Er-PS distance to achieve better FRET. Furthermore, an outer non-emitting protective Y3+ shell and a conducting Yb3+ shell reduced surface quenching and Er3+-to-Nd3+ energy back transfer effects, respectively. The upconversion FRET and downshifting emission efficiencies were simultaneously optimised by adjusting the thickness of the Y3+ shell, and the FRET efficiency was at least 3.7 times that of the reference NaYF4:Yb,Er@Yb@Nd,Yb@Y in a photodynamic therapy (PDT) model.

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The photocatalytic performance of a novel Nd-SiO2-TiO2 nanocomposite catalyst prepared by a sol-gel method was examined in the degradation of Rhodamine B (RhB), a notorious organic compound present in dye wastewaters. The prepared samples were characterized by low-temperature N2 adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectroscopy (DRS). Fourier-transform infrared (FT-IR) spectroscopic analysis indicated the enhanced chemical bonding of O--Ti and O--Ti--O with introduction of Nd and SiO2 dopant species into TiO2. The Nd-SiO2-TiO2 nanocomposite was found to exhibit a much higher photo- catalytic activity toward the decomposition of RhB under both UV and visible light irradiation as compared to a commercial TiO2 photocatalyst. The photodegradation efficiency of RhB (5 mg/L) was greater than 93% under visible light irradiation after 90 min. Addition of SiO2 was shown to not only inhibit crystal growth and TiO2 anatase-to-rutile phase transformation, but also enhance the adsorption of organic compounds. Nd doping has been suggested for slowing down the radiative recombination of photo-generated electrons and holes in TiO2, extending the photocatalyst light response to the visible region. The synergetic effects between Nd-SiO2 and TiO2 are described; the prepared Nd-SiO2-TiO2 represents a noteworthy contribution to the study of pollutant degradation in dye wastewaters.

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The in vivo biological applications of upconversion nanoparticles (UCNPs) prefer excitation at 700-850 nm, instead of 980 nm, due to the absorption of water. Recent approaches in constructing robust Nd(3+) doped UCNPs with 808 nm excitation properties rely on a thick Nd(3+) sensitized shell. However, for the very important and popular Förster resonance energy transfer (FRET)-based applications, such as photodynamic therapy (PDT) or switchable biosensors, this type of structure has restrictions resulting in a poor energy transfer. In this work, we have designed a NaYF4:Yb/Ho@NaYF4:Nd@NaYF4 core-shell-shell nanostructure. We have proven that this optimal structure balances the robustness of the upconversion emission and the FRET efficiency for FRET-based bioapplications. A proof of the concept was demonstrated for photodynamic therapy and simultaneous fluorescence imaging of HeLa cells triggered by 808 nm light, where low heating and a high PDT efficacy were achieved.

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Nd3+-sensitized quenching-shield sandwich-structured upconversion nanoparticles are reported, which exhibit highly efficient upconversion photoluminescence under excitation by an 800 nm continuous-wave laser. The transition-layer structure is essential to bridge energy transfer from the sensitizer to the activator and simultaneously block energy back-transfer from the activator to the sensitizer. These 800 nm-excited upconversion nanoparticles are a key step toward the development of upconversion nanophosphors for biological applications.

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Optical waveguides were fabricated in neodymium-doped silicate glass by using a low-repetition-rate (1 kHz) femtosecond laser inscription. Two different types of waveguide structure are fabricated. In the first, guiding occurs in the focal spot. In the second, guiding occurs in the region between the two filaments. The near-field intensity distribution, propagation loss, index profile reconstruction, and calculation of the modal intensity distribution by the beam propagation method of these waveguides are presented. On the basis of near-field intensity distribution of the light guided through the waveguides and the propagation loss measurement, the optimum writing conditions such as the pulse energy and scan velocity were determined. The waveguide written with 2.2 µJ pulse energy and 50 µm/s scan velocity shows strong guidance at 632.8 nm, with an index contrast of 7 × 10(-4) and a propagation loss of ~0.8 dB/cm.

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Intense near-infrared luminescence of Nd(3+) and Tm(3+) ions in the region of 860-1550 nm were achieved in 10-15 nm wurtzite ZnO nanocrystals fabricated by a facile sol-gel process. The optical properties of Nd(3+) and Tm(3+) ions were investigated by using the steady-state and time-resolved laser spectroscopy. Due to the well-ordered crystal-field surroundings experienced by Nd(3+) and Tm(3+) ions, sharp and well resolved emission lines of Nd(3+) and Tm(3+) ions were identified at 4-300 K. Time-resolved luminescence and decay behaviors of the (4)F(3/2)-->(4)I(11/2) transition of Nd(3+) ions reveal the existence of multiple Nd(3+) sites in ZnO nanocrystals.

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A novel Nd(3+)-doped lead fluorosilicate glass (NPS glass) is prepared by a two-step melting process. Based on the absorption spectrum a Judd-Ofelt theory analysis is made. The emission line width of NPS glass is 44.2 nm. The fluorescence decay lifetime of the (4)F(3/2) level is 586+/-20 microsec, and the stimulated emission cross-section is 0.87x10(-20)cm(2)at 1056 nm. A laser oscillation is occurred at 1062 nm when pumped by 808 nm Diode Laser. The slope efficiency is 23.7% with a 415 mJ threshold. It is supposed that NPS glass is a good candidate for using in ultra-short pulse generation and amplification by the broad emission bandwidth and long fluorescence lifetime.

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