Plasmonic enhancement induced by metallic nanostructures is an effective strategy to improve the upconversion efficiency of lanthanide-doped nanocrystals. It is demonstrated that plasmonic enhancement of the upconversion luminescence (UCL) of single NaYF :Yb /Er /Mn nanocrystal can be tuned by tailoring scattering and absorption cross sections of gold nanorods, which is synthesized wet chemically. The assembly of the single gold nanorod and single upconversion nanocrystal is achieved by the atomic force microscope probe manipulation. By selecting two kinds of gold nanorods with similar longitudinal surface plasmon resonance wavelength but different diameters (27.3 and 46.7 nm), which extinction spectra are separately dominant by the absorption and scattering, the maximum UCL enhancement by a factor of 110 is achieved with the 46.7 nm-diameter gold nanorod, while it is 19 for the nanorod with the diameter of 27.3 nm. Such strong enhancement with the larger gold nanorod is due to stronger scattering ability and greater extent of the near-field enhancement. The enhanced UCL shows a strong dependence on the excitation polarization relative to the nanorod long axis. Time-resolved measurements and finite-difference time-domain simulations unveil that both excitation and emission processes of UCL are accelerated by the nanorod plasmonic effect.
The use of one-dimensional nano- and microstructured semiconductor and lanthanide materials is attractive for polarized-light-emission studies. Up-conversion emission from single-nanorod or anisotropic nanoparticles with a degree of polarization has also been discussed. However, microscale arrays of nanoparticles, especially well-aligned one-dimensional nanostructures as well as their up-conversion polarization characterization, have not been investigated yet. Herein, we present a novel and facile paradigm for preparing highly aligned arrays of lanthanide-doped KMnF (KMnF:Ln) perovskite nanowires, which are good candidates for polarized up-conversion emission studies. These perovskite nanowires, with a width of 10 nm and length of a few micrometers, are formed through the oriented attachment of KMnF:Ln nanocubes along the [001] direction. By the employment of KMnF:Ln nanowire gel as nanoink, a direct-writing method is developed to obtain diverse types of aligned patterns from the nanoscale to the wafer scale. Up-conversion emissions from the highly aligned nanowire arrays are polarized along the array direction with a polarization degree up to 60%. Taking advantage of microscopic nanowire arrays, these polarized up-conversion emissions should offer potential applications in light or information transportation.
Near-infrared (NIR) single-photon source plays a key role in a wide range of applications in quantum technology. In particular, in quantum communication, the NIR wavelength operation perfectly matches the relatively low-attenuation transmission window of the optical fiber, which attracts more and more research interest. Here, we report the room temperature single-photon emission from single point defects in the aluminum gallium nitride (AlGaN) film. The obtained single-photon emission covers from 720 to 930 nm and exhibits highly linear polarization and high photon brightness. This may provide a platform for future integrated on-chip quantum photonic devices.
Point defects in the wide bandgap III-nitride semiconductors are recently reported to be one kind of the most promising near-infrared (NIR) quantum emitters operating at room temperature (RT). But the...
Optical polarization has attracted considerable research attention by extra detection dimension in angular space, flourishing modern optoelectronic applications. Nonetheless, purposive polarization controlling at nanoscales and even at the single-particle level constitutes a challenge. Plasmonic nanoantenna opens up new perspectives in polarization state modification. Herein, we report angular-dependent upconversion luminescence (UCL) of rare-earth ions doped upconversion nanoparticles (UCNPs) in both emission and excitation polarization via constructing angularly anisotropic plasmonic local-field distributions in gold nanorods (Au NRs) antennae with different configurations at a single-particle level. The UCL of UCNP tailored by plasmonic Au NRs nanoantennae is enhanced and exhibits linear polarization. The highest enhancement factor of 138 is obtained in the collinear Au NR-UCNP-Au NR configuration under parallel excitation. Simultaneously, the maximum degree of linear polarization (DOLP) of UCL with factors of 85% and 81% are achieved in the same structure in emission and excitation polarization measurements, respectively. The observed linear polarizations and UCL enhancements are due to varied resonant responses at 660 nm and the anisotropic near-field enhancement in different nanoantennae-load UCNP. The theoretical simulations reveal the periodic changing of near-field enhancement factors of nanoantennae in angular space with the incident light polarization angles and are well-matched with the experimental results.
The heterogeneous epitaxial system of BaTiO3/Ge (BTO/Ge) is of great interest for both fundamental research and device applications, thanks to its quasi-lattice-matching feature and the integration of functional oxides on semiconductors. Currently, the heteroepitaxial growth of crystalline BTO films on Ge includes the utilization of ultrahigh vacuum tools and complex surface passivation pre-treatment as well as careful control of oxygen partial pressure during the growth. Meanwhile, oxygen vacancies in oxides strongly impact their structural and electrical properties. Here, we report a facile method to directly grow single crystalline BTO films on Ge using pulsed laser deposition. The strict control of oxygen partial pressure ensures a sharp interface with an atom-to-atom registry and also leads to the oxygen-deficient characteristics of BTO. The epitaxial relationship of BTO and Ge is [110] BTO (001)//[100] Ge (001). Detailed crystallographic studies on BTO films with different thicknesses show that, for the films with a thickness less than 20 nm, BTO shows a mixture of tetragonal and cubic phases due to the oxygen vacancies and the strain from the Ge substrate and the cubic phase eventually dominates as the film thickness increases. Such oxygen-deficient BTO films reveal conducting characteristics rather than dielectric properties. The oxygen vacancies can be partly “cured” after a low temperature annealing process. These results not only demonstrate the possibility to directly grow single crystalline oxides on semiconductors without surface passivation but also highlight the importance of oxygen vacancies and lattice strain on the crystallographic and electrical properties of BTO films.
Single-photon emitters (SPEs) are attractive as integrated platforms for quantum applications in technologically mature wide-bandgap semiconductors since their stable operation at room temperature or even at high temperatures. In this study, we systematically studied the temperature dependence of the SPE in AlGaN micropillars by experiment. The photoluminescence (PL) spectrum, PL intensity, radiative lifetime and second-order autocorrelation function measurements are investigated over the temperature range from 303-373 K. The point defects of AlGaN show strong zero phonon line (ZPL) in the wavelength range of 800-900 nm and highly antibunched photon emission even up to 373 K. Our study reveals a possible mechanism for linewidth broadening in AlGaN SPE at high temperatures. This indicates a possible key for on-chip integration applications based on this material operating at high temperatures.
Vertically aligned gold nanorod arrays have attracted much attention for their fascinating optical properties. Different from longitudinal surface plasmon wavelength (LSPW) and edge-to-edge spacing of gold nanorods, the role of gold nanorod diameter in plasmonic enhancement ability of vertical gold nanorod arrays has rarely been explored. In this work, we selected gold nanorods with similar LSPW but two different diameters (22 and 41 nm), the optical properties of which are dominated by absorption and scattering cross sections, respectively. The vertically aligned arrays of these gold nanorods formed by evaporation self-assembly are coupled with nonlinear ZnO nanocrystal films spin-coated on their surfaces. It was found that the gold nanorod array with a larger diameter can enhance the second harmonic generation (SHG) of ZnO nanofilm by a factor of 27.0, while it is about 7.3 for the smaller gold nanorod array. Theoretical simulations indicate that such stronger enhancement of the larger vertical gold nanorod array compared with the smaller one is due to its stronger scattering ability and greater extent of near-field enhancement at SHG fundamental wavelength. Our work shows that the diameter of gold nanorods is also an important factor to be considered in realizing strong plasmon enhancement of vertically aligned gold nanorod arrays.
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