Donglei Zhou

Local Field Modulation Induced Three‐Order Upconversion Enhancement: Combining Surface Plasmon Effect and Photonic Crystal Effect

A 2D surface plasmon photonic crystal (SPPC) is achieved by implanting gold nanorods onto the periodic surface apertures of the poly(methyl methacrylate) (PMMA) opal photonic crystals. On the surface of the SPPC, the overall upconversion luminescence intensity of NaYF4 :Yb(3+) , Er(3+) under 980 nm excitation is improved more than 10(3) fold. The device is easily shifted to a transparent flexible substrate, applied to flexible displays.

Highly Efficient LiYF4:Yb3+, Er3+ Upconversion Single Crystal under Solar Cell Spectrum Excitation and Photovoltaic Application

Luminescent upconversion is a promising way to harvest near-infrared (NIR) sunlight and transforms it into visible light that can be directly absorbed by active materials of solar cells and improve their power conversion efficiency (PCE). However, it is still a great challenge to effectively improve the PCE of solar cells with the assistance of upconversion. In this work, we demonstrate the application of the transparent LiYF4:Yb(3+), Er(3+) single crystal as an independent luminescent upconverter to improve the PCE of perovskite solar cells. The LiYF4:Yb(3+), Er(3+) single crystal is prepared by an improved Bridgman method, and its internal quantum efficiency approached to 5.72% under 6.2 W cm(-2) 980 nm excitation. The power-dependent upconversion luminescence indicated that under the excitation of simulated sunlight the (4)F(9/2)-(4)I(15/2) red emission originally results from the cooperation of a 1540 nm photon and a 980 nm photon. Furthermore, when the single crystal is placed in front of the perovskite solar cells, the PCE is enhanced by 7.9% under the irradiation of simulated sunlight by 7-8 solar constants. This work implies the upconverter not only can serve as proof of principle for improving PCE of solar cells but also is helpful to practical application.

Observation of Considerable Upconversion Enhancement Induced by Cu2–xS Plasmon Nanoparticles

Localized surface plasmon resonances (LSPRs) are achieved in heavily doped semiconductor nanoparticles (NPs) with appreciable free carrier concentrations. In this paper, we present the photonic, electric, and photoelectric properties of plasmonic Cu2-xS NPs/films and the utilization of LSPRs generated from semiconductor NPs as near-infrared antennas to enhance the upconversion luminescence (UCL) of NaYF4:Yb(3+),Er(3+) NPs. Our results suggest that the LSPRs in Cu2-xS NPs originate from ligand-confined carriers and that a heat treatment resulted in the decomposition of ligands and oxidation of Cu2-xS NPs; these effects led to a decrease of the Cu(2+)/Cu(+) ratio, which in turn resulted in the broadening, decrease in intensity, and red-shift of the LSPRs. In the presence of a MoO3 spacer, the UCL intensity of NaYF4:Yb(3+),Er(3+) NPs was substantially improved and exhibited extraordinary power-dependent behavior because of the energy band structure of the Cu2-xS semiconductor. These findings provide insights into the nature of LSPR in semiconductors and their interaction with nearby emitters and highlight the possible application of LSPR in photonic and photoelectric devices.

Doping Lanthanide into Perovskite Nanocrystals: Highly Improved and Expanded Optical Properties

Cesium lead halide (CsPbX3) perovskite nanocrystals (NCs) have demonstrated extremely excellent optical properties and great application potentials in various optoelectronic devices. However, because of the anion exchange, it is difficult to achieve white-light and multicolor emission for practical applications. Herein, we present the successful doping of various lanthanide ions (Ce3+, Sm3+, Eu3+, Tb3+, Dy3+, Er3+, and Yb3+) into the lattices of CsPbCl3 perovskite NCs through a modified hot-injection method. For the lanthanide ions doped perovskite NCs, high photoluminescence quantum yield (QY) and stable and widely tunable multicolor emissions spanning from visible to near-infrared (NIR) regions are successfully obtained. This work indicates that the doped perovskite NCs will inherit most of the unique optical properties of lanthanide ions and deliver them to the perovskite NC host, thus endowing the family of perovskite materials with excellent optical, electric, or magnetic properties.

Paper-based upconversion fluorescence resonance energy transfer biosensor for sensitive detection of multiple cancer biomarkers.

A paper-based upconversion fluorescence resonance energy transfer assay device is proposed for sensitive detection of CEA. The device is fabricated on a normal filter paper with simple nano-printing method. Upconversion nanoparticles tagged with specific antibodies are printed to the test zones on the test paper, followed by the introduction of assay antigen. Upconversion fluorescence measurements are directly conducted on the test zones after the antigen-to-antibody reactions. Furthermore, a multi-channel test paper for simultaneous detection of multiple cancer biomarkers was established by the same method and obtained positive results. The device showed high anti-interfere, stability, reproducible and low detection limit (0.89 ng/mL), moreover it is very easy to fabricate and operate, which is a promising prospect for a clinical point-of-care test.

Plasmon-Enhanced Upconversion Luminescence on Vertically Aligned Gold Nanorod Monolayer Supercrystals.

Upconversion nanophosphor is attracting worldwide interests owing to its unique optical properties and great application potentials. However, it is still a great challenge to effectively improve the efficiency/strength of upconversion nanophosphor. Plasmonic modulation is a promising way to solve this bottleneck. In this work, we present a simple yet versatile concept on magnifying upconversion luminescence of NaYF4:Yb(3+), Er(3+) nanocrystals through local field manipulation of surface plasmon. Gold nanorods were directionally assembled into a vertically aligned monolayer supercrystals over large areas. The FDTD simulation indicates that the electromagnetic field strength |E|(2) can be improved about 113 folds at the hot spots of monolayer supercrystals. After optimization, on the surface of the vertically aligned monolayer supercrystals, the overall upconversion luminescence intensity of NaYF4:Yb(3+), Er(3+) under 980 nm excitation was improved more than 35 fold.

Cerium and Ytterbium Codoped Halide Perovskite Quantum Dots: A Novel and Efficient Downconverter for Improving the Performance of Silicon Solar Cells

Quantum cutting can realize the emission of multiple near-infrared photons for each ultraviolet/visible photon absorbed, and has potential to significantly improve the photoelectric conversion efficiency (PCE) of solar cells. However, due to the lack of an ideal downconversion material, it has merely served as a principle in the laboratory until now. Here, the fabrication of a novel type of quantum cutting material, CsPbCl1.5 Br1.5 :Yb3+ , Ce3+ nanocrystals is presented. Benefiting from the larger absorption cross-section, weaker electron-phonon coupling, and higher inner luminescent quantum yield (146%), the doped perovskite nanocrystals are successfully explored as a downconverter of commercial silicon solar cells (SSCs). Noticeably, the PCE of the SSCs is improved from 18.1% to 21.5%, with a relative enhancement of 18.8%. This work exhibits a cheap, convenient, and effective way to enhance the PCE of SSCs, which may be commercially popularized in the future.

Modulation of upconversion white light emission in PMMA/NaYF 4 :Yb 3+ , Er 3+ , Tm 3+ composite photonic crystals

In recent years, spontaneous emission modulation of emitters in photonic crystals (PCs) has been widely reported. However, the modulation of PCs on upconversion (UC) white light emission has been rarely studied. In this Letter, triply doped PMMA/NaYF(4):Yb(3+), Er(3+), Tm(3+) composite photonic crystals were successfully fabricated and white light emission was obtained. It is interesting to observe that the chromaticity could be conveniently tuned by changing the photonic stop band (PSB), the incident angle, or the power of the excitation light.

Fabrication of Au-Ag nanocage@NaYF4@NaYF4:Yb,Er core-shell hybrid and its tunable upconversion enhancement

Localized electric filed enhancement by surface plasmon resonance (SPR) of noble metal nanoparticles is an effective method to amplify the upconversion luminescence (UCL) strength of upconversion nanoparticles (UCNPs), whereas the highly effective UCL enhancement of UCNPs in colloids has not been realized until now. Here, we designed and fabricated the colloidal Au-Ag nanocage@NaYF4@NaYF4:Yb,Er core-shell hybrid with different intermediate thickness (NaYF4) and tunable SPR peaks from visible wavelength region to NIR region. After the optimization of the intermediate spacer thickness (~7.5 nm) of NaYF4 NPs and the SPR peak (~950 nm) of noble metal nanoparticles, an optimum enhancement as high as ~25 folds was obtained. Systematic investigation indicates that UCL enhancement mainly originates from the influence of the intermediate spacer and the coupling of Au-Ag nanocages with the excitation electromagnetic field of the UCNPs. Our findings may provide a new thinking on designing highly effective metal@UCNPs core-shell hybrid in colloids.

Semiconductor plasmon-sensitized broadband upconversion and its enhancement effect on the power conversion efficiency of perovskite solar cells

Photon upconversion (UC) is an attractive strategy to substantially enhance the power conversion efficiency (PCE) of solar cells via upconverting unavailable near-infrared sunlight to available visible light. However, to date, it is almost infeasible to achieve effective PCE improvement of solar cells with the assistance of UC materials, limited by their poor UC efficiency and extremely weak and narrowband near-infrared absorption. Here, we demonstrate the efficient photon energy UC in semiconductor plasmon mCu2−xS@SiO2@Er2O3 (mCSE) nanocomposites, where the broadband semiconductor plasmon (800–1600 nm) of mCu2−xS serves as an antenna to sensitize UC of Er2O3 nanoparticles. The overall upconversion luminescence (UCL) of the composites was dramatically enhanced by a factor of ∼1000, with a maximal inner quantum efficiency of 14.3%. The excitation range was expanded, ranging from 800 to 1600 nm. As a proof-of-concept, the highly efficient mCSE nanocomposites were utilized to improve the PCE of perovskite solar cells (PSCs). The expansion of the near-infrared response (800–1000 nm) and considerable improvement of the PCE were obtained, with an optimum PCE of 17.8%. The mCSE composites in PSCs enhanced the photocurrent via electron transfer from oxygen defects to the conduction band of TiO2 under irradiation of one sunlight. Under irradiation of 15 suns, the electron transfer and reabsorption of UCL both contributed to the enhancement of PCE. Our work can provide an insightful thought on boosting UC efficiency as well as broadening the PCE of PSCs.