The presence of manganese ions (Mn 2+ ) in Yb/Er-co-doped nanomaterials results in suppressing green (545 nm) and enhancing red (650 nm) upconversion (UC) emission, which can achieve single-red-band emission to enable applications in bioimaging and drug delivery. Here, we revisit the tunable multicolor UC emission in a single Mn 2+ -doped β-NaYF 4 :Yb/Er microcrystal which is synthesized by a simple one-pot hydrothermal method. Excited by a 980 nm continuous wave (CW) laser, the color of the single β-NaYF 4 :Yb/Er/Mn microrod can be tuned from green to red as the doping Mn 2+ ions increase from 0 to 30 mol%. Notably, under a relatively high excitation intensity, a newly emerged emission band at 560 nm ( 2 H 9/2 → 4 I 13/2 ) becomes significant and further exceeds the traditional green (545 nm) emission. Therefore, the red-to-green (R/G) emission intensity ratio is subdivided into traditional (650 to 545 nm) and new (650 to 560 nm) R/G ones. As the doped Mn 2+ ions increase, these two R/G ratios are in lockstep with the same tunable trends at low excitation intensity, but the tunable regions become different at high excitation intensity. Moreover, we demonstrate that the energy transfer (ET) between Mn 2+ and Er 3+ contributes to the adjustment of R/G ratio and leads to tunable multicolor of the single microrod. The spectroscopic properties and tunable color from the single microrod can be potentially utilized in color display and micro-optoelectronic devices.
β-NaYF4:Yb,Er upconversion nanoparticles (UCNPs) were synthesized by a one-pot solvothermal method. The UCNPs were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to prove that they possessed hexagonal crystal phase with uniform particle size distribution. The cationic solid lipid nanoparticles (CSLNs) were then obtained by coating the UCNPs with a lipid. Further analysis by FTIR, XRD and TEM indicated the lipid can successfully coat UCNPs, and the coating process had no obvious influences on morphology and crystallization of the UCNPs. Furthermore, the CSLNs were used for bioimaging in cells and delivering small interfering RNA (siRNA). Cellular bioimaging and upconversion luminescence studies clearly demonstrated that the CSLNs could effectively enter into cells with the help of the lipid. Silencing assays and cytotoxicity in A549 cells convincingly showed that the CSLNs could effectively deliver siRNA and possessed low cytotoxicity and good biocompatibility. Thus, the bifunctional CSLNs could be used as a potential candidate in bioimaging and therapeutic applications.
β-NaYF4:Yb,Er,Gd fluorescent nanorods were successfully coupled to a reduced TiO2(UCNPs@R-TiO2) nanocomposite and applied to visible-light catalytic sterilization under 980 nm near-infrared (NIR) light illumination. The UCNPs (β-NaYF4:Yb,Er,Gd) absorb the NIR light and emit red and green light. The visible light can be absorbed by the R-TiO2(Eg = 2.8 eV) for the photocatalytic reaction. About 98.1% ofEscherichia coliwere effectively killed upon 12 min of NIR light irradiation at a minimum inhibitory concentration (MIC) of 40 μg/mL UCNPs@R-TiO2nanocomposite. The bactericidal properties were further evaluated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis. We found that the high bactericidal activity was due to the synergistic effect between the UCNPs and R-TiO2. Moreover, the UCNPs show excellent upconversion luminance properties, and the introduction of visible-light-absorbed R-TiO2nanoparticles (2.8 eV) was conducive to the efficient separation and utilization of photogenerated electron-hole pairs.
Lele Qiu,Yulin Yang,Guohua Dong,Debin Xia,Mengru Li,Xiao Fan,Ruiqing Fan
As for the solution-processed MAPbI 3 film, the pinholes and gaps are an inevitable and undesirable phenomenon, which can usually lead to serious interface charge recombination due to the penetration of hole transport materials in perovskite solar cells (PSCs). Herein, a hydrophobic β-NaYF 4 :Yb,Er up-conversion ultrathin layer with particle size ca. 6 nm was first applied to modify the MAPbI 3 film for optimizing the surface of perovskite film. Thereby, the corresponding PSCs yield a significantly enhanced power conversion efficiency of 15.17% compared with that (13.32%) of the pristine PSCs. Furthermore, the PSCs also have a good stability in air atmosphere (relative humidity ≤45%) because of the introduction of this hydrophobic material. After a series of detailed investigations and comparison, it can be easily concluded that the filled pinholes and gaps in perovskite films via β-NaYF 4 :Yb,Er nanoparticles is the main reason for the performance enhancement of the β-NaYF 4 :Yb,Er based PSCs, which can result in an enhanced hole extraction efficiency and reduced interface charge recombination. As a conclusion, it is a feasible and effective approach for improving the photovoltaic performance of PSCs by filling up the pinholes and gaps in perovskite films with up-conversion ultrathin layers.
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