Xuejie Zhang

Tunable emission from green to red in the GdSr2AlO5:Tb3+,Eu3+ phosphor via efficient energy transfer

Herein, a series of GdSr2AlO5:Tb3+,Eu3+ phosphors were successfully synthesized through a high temperature solid-state reaction, and their crystal structures as well as photoluminescence properties were investigated in detail. Compared to the intense emission of 5D0 → 7F1 or 5D0 → 7F2 transition of Eu3+, another strong emission corresponding to 5D0 → 7F4 was observed. Concentration quenching is not obvious in Tb3+ or Eu3+-doped GdSr2AlO5 because structure isolation and energy transfer (ET) of Gd3+ → Eu3+ and Gd3+ → Tb3+ were found. Moreover, the energy transfer process from Tb3+ to Eu3+ was verified by the overlap of luminescence spectra and the variation of lifetime. Energy transfer mechanism was determined to be a dipole–dipole interaction, and ET efficiency as well as quantum efficiency were also obtained. Moreover, the emission color of GdSr2AlO5:Tb3+,Eu3+ can be tuned from green to red by altering the ratio of Tb3+/Eu3+. These results indicate that the GdSr2AlO5:Tb3+,Eu3+ phosphor is a promising single-component white light-emitting phosphor.

Ultrastable red-emitting phosphor-in-glass for superior high-power artificial plant growth LEDs

Ultrastable red-emitting phosphor-in-glass (PiG) consisting of 3.5MgO·0.5MgF2·GeO2:Mn4+ (MMG:Mn4+) phosphor in a glass matrix was prepared for superior artificial plant growth LEDs (PGLs). These obtained PiG plates show a thermal conductivity of 1.671 W m−1 K−1 and an external quantum efficiency of 27.5%, which provides the strong foundation for the application in high-power artificial plant growth LEDs (PGLs). Furthermore, a proof-of-concept PGL using 36 pieces of the title PiG plate and 420 nm-blue LED chip was fabricated. The combination of ∼420 nm from chip and the ∼659 nm chip from the MMG:Mn4+ phosphor provide a well-matched spectrum with the absorption bands of photosynthetic pigments and the phytochrome (PR and PFR) of most green plants. As expected, the as-fabricated PGL-treated milk-Chinese cabbage cultured in the indoor plant factory showed that after 15 day-irradiation, the plant biomass was nearly 48.9% greater in treated sample than those cultured using the general R-B LED lamps. Further analysis also demonstrated that promotive effect can also be obtained in the level of ascorbic acid, soluble protein, soluble sugar and total chlorophyll. The PiG strategy presented in this paper afforded superior high-power artificial plant growth LEDs, which are crucial in the application of ecological agriculture.

Bioimaging Application and Growth-Promoting Behavior of Carbon Dots from Pollen on Hydroponically Cultivated Rome Lettuce

Carbon dots (CDs) obtained from rapeseed pollen with a high production yield, good biocompatibility, good water solubility, low cost, and simple synthesis are systematically characterized. They can be directly added to Hoagland nutrient solution for planting hydroponically cultivated Lactuca sativa L. to explore their influence on the plants at different concentrations. By measuring lettuce indices of growth, morphology, nutrition quality, gas exchange, and content of photosynthetic pigment, amazing growth-promotion effects of CDs were discovered, and the mechanism was analyzed. Moreover, the in vivo transport route of CDs in lettuce was evaluated by macroscopic and microscopic observations under UV light excitation. The results demonstrate that pollen-derived CDs can be potentially used as a miraculous fertilizer for agricultural applications and as a great in vivo plant bioimaging probe.

Pollen derived blue fluorescent carbon dots for bioimaging and monitoring of nitrogen, phosphorus and potassium uptake in Brassica parachinensis L.

Carbon dots (CDs), synthesized from biological sources, have attracted attention in bioimaging and bioscience due to their low cytotoxicity, water-soluble nature, and biocompatibility. However, there are a few reports on the absorption of elements and tracking the transporting systems in plants. Herein, we report pollen-CDs synthesized by a hydrothermal method that emit blue light under excitation of UV light, which can be used to track the absorption of nitrogen, phosphorus, and potassium, and mark the biological transport systems in Brassica parachinensis L. The pollen-CDs were transported via the vascular system of Brassica parachinensis L., confirmed by the confocal images. TEM results demonstrated that the pollen-CDs were enriched in the periplasmic space, which helps to enhance the absorption efficiency of potassium and inhibit the accumulation of nitrates in Brassica parachinensis L. The hydroponic experiment results demonstrated that Brassica parachinensis L. had the highest yield of 42.90 mg when 3.5 mg L−1 pollen-CDs were added to the nutrient solution. All the results demonstrated that the pollen-CDs have potential for application in hydroponically grown vegetables and biocompatible studies in vitro/in vivo imaging.

Enhanced luminescence performance of CaO:Ce3+,Li+,F− phosphor and its phosphor-in-glass based high-power warm LED properties

To obtain white light-emitted diodes (wLEDs) with a low correlated color temperature (CCT) and a high color rendering index (CRI), red-emission is indispensable in their emission spectra. Herein, CaO:Ce3+,Li+,F− yellow phosphors with more red spectral component have been prepared via a high temperature solid-state reaction. As compared to the F− undoped samples, CaO:Ce3+,Li+,F− phosphor have lower critical doping concentration of Ce3+ and show stronger luminescence. At the critical concentration, a quantum efficiency of 66.4% and enhanced thermal and chemical stability were obtained in CaO:Ce3+,Li+,F−. Furthermore, a CaO:Ce3+,Li+,F−-based phosphor-in-glass (PiG) using the red-emitting glass system with the composition of SiO2–Na2CO3–Al2O3–CaO:Eu3+ as the host material was constructed and used for high-power white LED applications. Such PiG samples with different phosphor doping concentrations can satisfy various light color demands and display higher reliability than the CaO:Ce3+,Li+,F− phosphor. An optimal PiG-based wLED exhibits color coordinates of (0.3769, 0.3386), a CCT of 3774 K, a CRI of 82.5 and a LE of 73.1 when the mass ratio of phosphor to glass matrix was 7u2006:u200650 in PiG. Moreover, such PiG-based wLED also showed acceptable color stability under different drive currents. All the above results demonstrate that CaO:Ce3+,Li+,F− can be expected to be a potential alternative yellow phosphor for blue light excited PiG based warm wLEDs, particularly for high-power devices.

Preparation and properties of dual-mode luminescent NaYF4:Yb,Tm@SiO2/carbon dot nanocomposites

Herein, NaYF4:Yb,Tm@SiO2/carbon dot nanocomposites have been successfully fabricated by a facile route. The structure and morphology of the nanocomposites were characterized by SEM, TEM, XRD, FT-IR and XPS measurements. It was demonstrated that carbon dots were embedded well in the silica layer coating on the surface of NaYF4:Yb,Tm nanoparticles, leading to a relatively stable structure of the nanocomposites. The nanocomposites showed interesting dual-mode luminescence properties, i.e. blue green light under a 365 nm UV lamp and blue purple light under a 980 nm laser. They were utilized to achieve light conversion films, ion detection probes and cell imaging, suggesting their great potential in the fields of anti-counterfeiting and bioapplications.

Near-Ultraviolet to Near-Infrared Fluorescent Nitrogen-Doped Carbon Dots with Two-Photon and Piezochromic Luminescence

Carbon dots (CDs) have gained intensive interests owing to their unique structure and excellent optoelectronic performances. However, to acquire CDs with a broadband emission spectrum still remains an issue. In this work, nitrogen-doped CDs (N-CDs) with near-ultraviolet (NUV), visible, and near-infrared (NIR) emission were synthesized via one-pot solvothermal strategy, and the excitation-independent NUV and NIR emission and excitation-dependent visible emission were observed in the photoluminescence (PL) spectra of N-CDs. Moreover, the as-synthesized N-CDs displayed two-photon fluorescence emission. It is important to note that N-CDs also exhibited piezochromic luminescence with reversibility, in which the red- and blue-shifted PL with increasing applied pressure (0.07-5.18 GPa) and the red- and blue-shifted PL with releasing applied pressure (5.18 GPa to 1 atm) were developed for the first time. Combined with good hydrophilicity, high photobleaching resistance, and low toxicity, the piezochromic luminescence would greatly boost the valuable applications of N-CDs.

Enhanced persistent properties of Mn2+ activated CaZnOS

The red emitting CaZnOS:Mn2+ long persistent phosphor was successfully prepared via a conventional high-temperature solid-state reaction method. The persistent luminescence emission of Mn2+-doped CaZnOS phosphor was investigated for the first time. Rare-earth trivalent ions were used as co-dopants to obtain a brighter red afterglow and longer persistence time. The optical properties of the as-prepared samples have been investigated systematically by employing photoluminescence spectroscopy, persistent luminescence spectroscopy, afterglow decay curves and thermoluminescence curves. In light of the experimental results of this study, a possible mechanism of persistent luminescence was illustrated and discussed in detail. These investigations provide a new and efficient long persistent phosphor.