Hong Kong Polytechnic University

About: Hong Kong Polytechnic University is a education organization based out in Hong Kong, China. It is known for research contribution in the topics: Tourism & Population. The organization has 29633 authors who have published 72136 publications receiving 1956312 citations. The organization is also known as: HKPU & PolyU.

Electric-induced enhancement and modulation of upconversion photoluminescence in epitaxial BaTiO3:Yb/Er thin films.

Abstract: Spectroscopic tuning and enhancement of upconversion photoluminescence (PL) are highly desirable for understanding the physical processes of energy transition and for widespread applications, such as laser mediums, optical waveguides, display lighting, and biomedicine. To date, modification of the upconversion PL in phosphors excited by a given excitation source can normally be achieved through a conventional chemical approach, that is, changing the composition of host materials and/or doping ions, thus giving only a limited understanding of the detailed process of luminescence and applications. For instance, the variation of the PL in different hosts can be ascribed to the different crystal field around dopant ions of various symmetries. Low symmetry hosts typically exert a crystal field containing more uneven components around the dopant ions compared to high symmetry counterparts. However, the tuning of PL by chemical way is essentially an irreversible and ex-situ process. Therefore, it is unlikely to know from the kinetic process how the luminescence changes with structural symmetry through the conventional approach. Moreover, it is almost impossible to isolate the pure crystal-field effect from other extrinsic effects present in different samples such as chemical inhomogeneities and defects. Hence, it is much needed to find a pathway in varying the host s symmetry in the same material, leading to the modification of PL. In particular, an enhancement of upconversion still presents a significant challenge, although a breakthrough of plasmon-enhanced upconversion through very precise manipulation was recently presented. 11] To date, there are no reports of an established approach to modulate upconversion emission in an in-situ and real-time way. The unique crystal structure of ferroelectric materials provides us an opportunity to couple variables including electric field and temperature to crystal symmetry in a single compound. Approaches through the use of ferroelectric characteristics have recently proven successful in controlling the ferromagnetism, spin polarization, and photovoltaic effects. Comparatively, ferroelectric control of luminescence has not been exploited. Therefore, it is of great interest to take advantage of the properties of ferroelectric host in combination with the luminescent doping ions acting as sensitive probes for the structure and symmetry. PL in the specific materials system should be modulated in reversible, real-time and dynamical way under ferroelectric control that can be realized by electrically changing the structural symmetry. Herein, BaTiO3 (BTO) is selected as ferroelectric host because it has been regarded as a model system for investigating crystal structure transformation under mechanical stress, electric field, and temperature. Lanthanide Er ion is composed of an incompletely filled 4f inner shell and two closed outer shells. Actually, Er ion in doped hosts has been a spectroscopic probe for many applications, including ferroelectric domain imaging. Very recently, we have observed the effects of Er doping and measuring temperature on the upconversion emission in BTO:Er powders. Therefore, it is interesting to observe the influence of electric field on the upconversion spectra of Er doping ions. Herein, we present a new approach to enhance and modulate upconversion emission through applying a relatively low bias voltage to the lanthanide-doped BTO thin films.

Upconverting Near‐Infrared Light through Energy Management in Core–Shell–Shell Nanoparticles

Abstract: Lanthanide-doped upconversion materials, capable of converting low-density (< 1000 W cm ) near-infrared (NIR) excitation to ultraviolet (UV) and visible emissions, have generated a large amount of interests in the areas of information technology, biotechnology, energy, and photonics. Significantly, recent developments in the synthetic and multicolor tuning methods have allowed easy access to upconversion nanoparticles with well-defined phase and size, core–shell structure, optical emission, and surface properties. The technological advances provide promising applications in sensitive biodetection and advanced bioimaging without many of the constraints associated with conventional optical biolabels. Despite the attractions, further progress in using upconversion processes has been largely hindered because upconversion nanoparticles are typically sensitized by Yb ions that only respond to narrowband NIR excitation centered at 980 nm. The absorption of 980 nm light by the water component in biological samples usually limits deep tissue imaging and induces potential thermal damages to cells and tissues. Excitation of conventional upconversion nanoparticles at other wavelengths has been proposed to minimize the effect of water absorption. But the use of this technique is limited mainly by the largely sacrificed excitation efficiency. Efforts have also been devoted to tuning the NIR response of photon upconversion through integration of various sensitizers such as metal ions (e.g.; Nd, V or Cr) and organic dyes. The progress has resulted in visible emission by NIR excitation in the 700–900 nm range where the transparency of biological samples is maximal. However, upconversion emission across a broad range of spectra in these systems have not been demonstrated largely owing to the uncontrollable nonradiative processes. Herein, we describe a novel design, based on nanostructural engineering to separate unwanted electronic transitions for constructing a new class of materials displaying tunable upconversion emissions spanning from UV to the visible spectral region by single wavelength excitation at 808 nm. We also show that these nanoparticles can surpass the constraints associated with conventional upconversion nanoparticles for biological studies. The nanostructure design for management of energy transitions is depicted in Figure 1. A core–shell–shell nanoparticle platform is used to host light-harvesting, upconvert-

Leader-member exchange and member performance: a new look at individual-level negative feedback-seeking behavior and team-level empowerment climate.

Abstract: From a basis in social exchange theory, the authors investigated whether, and how, negative feedback-seeking behavior and a team empowerment climate affect the relationship between leader-member exchange (LMX) and member performance. Results showed that subordinates' negative feedback-seeking behavior mediated the relationship between LMX and both objective and subjective in-role performance. In addition, the level of a team's empowerment climate was positively related to subordinates' own sense of empowerment, which in turn negatively moderated the effects of LMX on negative feedback-seeking behavior.