Ding Zhou

Toward Efficient Orange Emissive Carbon Nanodots through Conjugated sp2‐Domain Controlling and Surface Charges Engineering

A strategy of achieving efficient orange emissive carbon nanodots (CNDs) with large sized conjugated sp(2) -domain is achieved in a solvothermal synthetic route using dimethylformamide as solvent, which is the basis of orange bandgap emission; enhanced orange emission with photoluminescent quantum yield of 46% is realized through surface charges engineering by surface metal-cation-functionalization.

Supra-(carbon nanodots) with a strong visible to near-infrared absorption band and efficient photothermal conversion

A novel concept and approach to engineering carbon nanodots (CNDs) were explored to overcome the limited light absorption of CNDs in low-energy spectral regions. In this work, we constructed a novel type of supra-CND by the assembly of surface charge-confined CNDs through possible electrostatic interactions and hydrogen bonding. The resulting supra-CNDs are the first to feature a strong, well-defined absorption band in the visible to near-infrared (NIR) range and to exhibit effective NIR photothermal conversion performance with high photothermal conversion efficiency in excess of 50%.

Electrostatic Assembly Guided Synthesis of Highly Luminescent Carbon-Nanodots@BaSO4 Hybrid Phosphors with Improved Stability

Carbon nanodots (CNDs)@BaSO4 hybrid phosphors are fabricated in an easy and low-cost process by sequentially assembling Ba2+ and SO42- ions onto the surface of carbon nanodots through electrostatic attraction. CNDs act as the nucleus to attract these reactive ions and provide the luminescent centers in the hybrid phosphors. This strategy is versatile for a variety of negatively charged CNDs with different emission colors. The advantage of the resultant hybrid phosphors is that their luminescence exhibits excellent thermal and photostability, as well as remarkable resistance to strong acid/alkali and common organic solvents. These merits allow for the fabrication of CNDs-based light-emitting diodes using the CNDs@BaSO4 hybrid phosphors as a color conversion layer.

Diode-pumped continuous wave and Q-switched operation of Nd:LuAG crystal

The continuous wave (CW) and passively Q-switched performances of Nd:LuAG crystal were demonstrated. With a laser diode as pump source, the CW output power of 2.18 W was obtained under the pump power of 4.62 W, corresponding to the optical conversion efficiency of 47.2% and the slope efficiency of 52.2%. For Q-switching experiments, the shortest pulse width, largest pulse energy, and highest peak power were measured to be 12 ns, 50.6 μJ, and 4.21 kW, respectively.

Spectroscopic characteristics and laser performance of Tm:CaYAlO4 crystal

The spectroscopic characteristics of Tm:CaYAlO4 crystal were studied. Continuous wave laser operation at 2 μm was achieved with a 6 at.% Tm:CaYAlO4 (Tm:CYA) crystal pumped by a fiber-coupled laser diode. The laser emits a maximum output power of 4.3 W with a slope efficiency as high as 46.7%. In addition, a wavelength tuning experiment on Tm:CYA crystal was performed showing the Tm:CYA laser could be continuously tuned from 1861 to 2046 nm using an intracavity CaF2 prism, suggesting the potential of this crystal for ultrashort pulse generation by mode-locking.

CW laser properties of Nd:GdYAG, Nd:LuYAG, and Nd:GdLuAG mixed crystals

Three mixed crystals, Nd:GdYAG, Nd:LuYAG, and Nd:GdLuAG, were grown by Czochralski method. We report the continuous-wave (CW) Nd:GdYAG, Nd:LuYAG, and Nd:GdLuAG laser operation under laser diode pumping. The maximum output powers are 4.11, 5.31, and 7.47 W, with slope efficiency of 73.0, 55.3, and 57.1%, respectively. With replacing Lu3+ or Y3+ ions with large Gd3+ ions, the pump efficiency increases.

Near‐Infrared Excitation/Emission and Multiphoton‐Induced Fluorescence of Carbon Dots

Carbon dots (CDs) have significant potential for use in various fields including biomedicine, bioimaging, and optoelectronics. However, inefficient excitation and emission of CDs in both near-infrared (NIR-I and NIR-II) windows remains an issue. Solving this problem would yield significant improvement in the tissue-penetration depth for in vivo bioimaging with CDs. Here, an NIR absorption band and enhanced NIR fluorescence are both realized through the surface engineering of CDs, exploiting electron-acceptor groups, namely molecules or polymers rich in sulfoxide/carbonyl groups. These groups, which are bound to the outer layers and the edges of the CDs, influence the optical bandgap and promote electron transitions under NIR excitation. NIR-imaging information encryption and in vivo NIR fluorescence imaging of the stomach of a living mouse using CDs modified with poly(vinylpyrrolidone) in aqueous solution are demonstrated. In addition, excitation by a 1400 nm femtosecond laser yields simultaneous two-photon-induced NIR emission and three-photon-induced red emission of CDs in dimethyl sulfoxide. This study represents the realization of both NIR-I excitation and emission as well as two-photon- and three-photon-induced fluorescence of CDs excited in an NIR-II window, and provides a rational design approach for construction and clinical applications of CD-based NIR imaging agents.

Preparation and application of carbon-nanodot@NaCl composite phosphors with strong green emission

Luminescent carbon nanodots (CDots) have attracted much attention, but their luminescence is usually quenched in solid state. Efficient green or yellow emissive CDot-based phosphors are scarce. In this work, green emissive CDot@NaCl composite phosphors were fabricated through a convenient, low cost and eco-friendly way by embedding green emissive CDots (g-CDot) in NaCl crystals. With the protection of NaCl host, the g-CDot@NaCl composite phosphors exhibit good photostability, significant resistance to organic solvents, and improved photoluminescence quantum yields up to 25%. White light-emitting diodes with tunable color temperatures (3944-5478K) and CIE coordinates have been realized based on the g-CDot@NaCl composite phosphors.

A passively Q-switched Er:LuYAG laser with a graphene saturable absorber

A stable passively Q-switched Er:LuYAG laser resonantly pumped by an Er, Yb co-doped fiber laser was demonstrated using a graphene-based saturable absorber. At an incident pump power of 5.5 W, a maximum average output power of 460 mW at a central wavelength of 1648 nm was obtained with a shortest pulse duration of 2.05 μs, a repetition rate of 78.9 kHz and a pulse energy of 5.84 μJ.

Tm:fiber laser in-band pumped Ho:LuAG laser with over 18 W output at 2124.5 nm

We describe efficient operation of a Ho:LuAG laser in-band pumped by a cladding-pumped narrow linewidth Tm fiber laser at ∼1907 nm. With 1.0 at % Ho3+-doped LuAG and an output coupler of 6% transmission, the laser had a threshold pump power of ∼0.85 W and generated 18.04 W of continuous-wave output power at 2124.5 nm for 35 W of incident pump power, corresponding to an average slope efficiency with respect to incident pump power of 53.4%.