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Plasmonic photothermal effect of metal nanoparticles has been used for efficient cancer therapy and catalysis. Here, we show the insulation of Plasmonic photothermal heat generated in Ag nanoparticles by a thin carbon shell and their application for solar desalination of seawater. Ag, carbon and Ag with carbon shells (Ag@C) nanoparticles were synthesized by a hydrothermal method. The absorption of Ag@C core/shell nanoparticles almost covers the whole visible light spectrum from red to violet, which can be tuned by changing the thickness of the carbon shells and the size ratio of Ag cores to carbon shells. Ag@C core/shell nanoparticles with the size of 50 nm@18 nm exhibit a photothermal conversion efficiency 44% higher than carbon nanoparticles. Importantly, it is observed that carbon shells have excellent heat insulation property so that the temperature decay lifetime of Ag nanoparticles is enhanced by 49% after coating with a thin carbon shell of 18 nm. Ag@C nanoparticles supported by anodic aluminum oxide (AAO) templates exhibit a desalination rate 1000% higher than the direct evaporation of seawater under simulated solar irradiation and 220% higher than that of AAO templates supported carbon nanospheres.

Plasmon enhanced upconversion luminescence has drawn extensive attention due to its advances in the fields of optical sensors, bio-detection and medical diagnosis. However, the coupling state between plasmon and upconversion emission is never clearly revealed. Here, we report a novel critical state in plasmon coupled upconversion nanoparticles (UCNPs) that has a long lifetime and is highly stimuli-responsive. The critical state is generated through the precise control over the coupling between plasmonic local field and optical near field. Platinum (Pt) film with thickness of ~7 nm is deposited on photonic crystals to form a periodic plasmonic antenna arrays. UCNPs with inert shells are embedded in plasmonic antenna arrays with a tunable plasmon coupling distance via the thickness control of inert shells. An ultrasensitive critical state is observed for the coupling distance of ~10 nm between Pt film and NaGdF4:Yb/Er luminescent core, accompanied with light confinement by NaYF4/NaGdF4 heterojunction shells. This critical-state can be employed as an ultrasensitive route for fluorescent detection of NH3 and the lowest detection of 0.47 ppm can be achieved that is about 34 times lower than ever reported.

In this work, we reported NaLuF4:Yb3+/Er3+ optical-magnetic bifunctional material by a facile hydrothermal method. The modulation of luminescent and magnetic properties by introducing the secondary phase NaMnF3 was investigated in detail. It was found that the multi-color emissions of the proposed material can be easily controlled due to the energy level match between the Mn and the lanthanide ions. In addition, these microcrystals presented paramagnetic and ferromagnetic property, and the relative intensity showed an opposite variation to the content of NaMnF3 phase. Finally, we briefly discussed the dye detection based on this bifunctional material as fluorescent probe, and the integral intensity ratio of red to green emission was found being sensitive to the concentration of the basic fuchsin (BF), and a detection limit of 0.0015 μg/ml was achieved. These findings can be helpful to understand NaMnF3 induced optical-magnetic property modulation and provide some applications in the biosensing and bioimaging area.

In this paper, we reported a multilayer metamaterial system with ultrahigh absorption, consisting of silver nanoring, upconversion nanoparticles(UCNPs) and silver film, which can dramatically enhance the upconversion emission. A simplified theoretical expression of the upconversion enhancement factor(EFupc) was derived, and the structure parameter and the local field-UCNPs coupling were considered for the EFupc analysis. It was found that the bottom silver film was crucial for the tremendous upconversion enhancement since it gave rise to a pronounced absorption peak and resulted in a strong field confinement of the 980 nm excitation light. Comparing with the nanodisk, the nanoring performed better in enhancing the upconversion, and an enhancement factor of ∼3.2 × 104 was achieved based on the numerical and theoretical analysis. This metamaterial system provided a novel approach in enhancing upconversion, and the research findings could be helpful to the design of biosensor and photovoltaic devices.

Here, NaLuF 4 :Yb 3+ /Er 3+ /Gd 3+ bifunctional microcrystals were successfully synthesized by hydrothermal method, which can emit ∼652 nm red light from Er 3+ -4f n electronic transition 4 F 9/2 - 4 I 15/2 and ∼542 nm green light from Er 3+ -4f n electronic transition 4 S 3/2 - 4 I 15/2 , under the excitation of 980 nm infrared light. The intensity ratio of red to green emission increases obviously with increasing the concentration of Gd 3+ from 0 mol% to 10 mol%. Meanwhile, the red shift is also observed which is ascribed to the difference in surface property. By introducing Dy 3+ ion into NaLuF 4 :Yb 3+ /Er 3+ , the intensity of both green and red emissions changes non-monotonously due to the energy exchange between Er 3+ and Dy 3+ , which reaches to the highest value when doping with 0.5 mol% Dy 3+ ion. The ferromagnetic property decreases with increasing the concentration of Gd 3+ ion while the paramagnetic property increases greatly. This is ascribed to the fact that the coexistence of light rare earth (Gd 3+ ) and heavy rare earth (Yb 3+ /Tm 3+ ) will lead to the anti-ferromagnetic coupling in the sub-lattices.

Pure red upconversion luminescence was observed from Er 3+ doped Yb 3 Al 5 O 12 powder synthesized by sol–gel method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) patterns revealed two phases Yb 3 Al 5 O 12 and Yb 2 O 3 coexisting as crystals. High resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) analysis showed that the luminescence was from Er 3+ in Yb 3 Al 5 O 12 . High pure red emission was obtained in all three samples with the emission intensity ratios of red to green (R/G) being 78, 110 and 136 respectively. It was found that Yb 3+ was a composition of the host Yb 3 Al 5 O 12 rather than a doped ion and still played a sensitizing role and the R/G was in a positive variation with the ratio of Yb 3+ /Er 3+ . The possible mechanism can be ascribed to the resonant energy transfer 4 F 7/2 (Er 3+ ) + 4 I 11/2 (Er 3+ ) → 2 2 F 9/2 (Er 3+ ) caused by the high content of Yb 3+ .

The as-cast and the heat-treated samples with the primary mole composition of (59.4 − x )ZnF 2 –40PbF 2 –0.1B 2 O 3 – x Yb 2 O 3 –0.5Er 2 O 3 ( x = 2, 4, 7, 10, 13) were synthesized. In the as-cast and the heat-treated samples with 13 mol% Yb 2 O 3 , the multi-band and the single red band upconversion (UC) lights were observed, respectively, under the excitation of a laser diode (LD) with excitation wavelength of 980 nm. For this interesting phenomenon, microstructure analysis revealed that the crystal phases and the distribution of Er 3+ ion has been changed by the heat-treatment and the mole ratio of Yb 3+ to Er 3+ ion in the neighbor environment of Er 3+ ion is increased from 0.74 to 16.96 which brought about the populating behavior variation of 4 F 7/2 and 4 F 9/2 levels of Er 3+ ions, to which the achieving of the dazzlingly single-narrow-band red light was ascribed.

A series of Er 3+ -doped and Er 3+ /Yb 3+ -codoped lead germanate (GP), lead tellurite (TP) and lead borate (BP) transparent oxyfluoride glasses were synthesized. Spectroscopic characteristics of these materials were systemically measured. The Judd–Ofelt parameters were calculated according to absorption spectra. F − ions have a strong effect on refractive index ( n ) and phonon energy of the host. Intense red and green upconversion is closely related to phonon energy, J–O parameters and sensitizer. The GPEY-2 glass (53GeO 2 –43PbF 2 –0.5Er 2 O 3 –2Yb 2 O 3 ) shows good transparency and fairly strong upconversion emissions.

Microstructure and up-conversion luminescence properties of Er3+ and Yb3+ co-doped PbF2–ZnF2–SiO2 oxyfluoride silicate were investigated. Up-conversion luminescence spectra consist of four bands centered at 408, 523, 541 and 660 nm which are similar to other Yb3+ and Er3+ co-doped up-conversion materials, but the violet emission near 408 nm accounting to 16.8% in overall intensity is much stronger than others. Another feature is that the change of the ratio of the intensity of the green to red emission is not monotonously. These phenomenon can be explained by micro dendrite crystal appeared in the as cast sample with 0.1 mol% Er3+. The dendrite crystal is identified to be β-PbF2 by X-ray diffraction in which the content of rare-earth ions, Yb3+ and Er3+, is determined to be ∼7.0 mol%. The violet emission near 408 nm of the sample with the concentration of 0.1 mol% Er3+ decreased to 1.6% after the heat treatment because of the diminish of the dendrite.