Glucose-derived water-soluble crystalline graphene quantum dots (GQDs) with an average diameter as small as 1.65 nm (∼5 layers) were prepared by a facile microwave-assisted hydrothermal method. The GQDs exhibits deep ultraviolet (DUV) emission of 4.1 eV, which is the shortest emission wavelength among all the solution-based QDs. The GQDs exhibit typical excitation wavelength-dependent properties as expected in carbon-based quantum dots. However, the emission wavelength is independent of the size of the GQDs. The unique optical properties of the GQDs are attributed to the self-passivated layer on the surface of the GQDs as revealed by electron energy loss spectroscopy. The photoluminescence quantum yields of the GQDs were determined to be 7-11%. The GQDs are capable of converting blue light into white light when the GQDs are coated onto a blue light emitting diode.

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Visualization of tumor vessels/metastasis and cerebrovascular architecture is vitally important for analyzing pathological states of brain diseases and a tumor's abnormal blood vessels to improve cancer diagnoses. In vivo fluorescence imaging using second near-infrared emission beyond 1500 nm (NIR-IIb) has emerged as a next generation optical imaging method with significant improvement in imaging sensitivity and spatial resolution. Unfortunately, a highly biocompatible probe capable of generating NIR-IIb emission with sufficient brightness and uniformed size is still scarce. Here, we have proposed the poly(acrylic acid) (PAA)-modified NaLnF 4 :40Gd/20Yb/2Er nanorods (Ln = Y, Yb, Lu, PAA-Ln-NRs) with enhanced downshifting NIR-IIb emission, high quantum yield (QY), relatively narrow bandwidth (∼160 nm), and high biocompatibility via Ce 3+ doping for high performance NIR-IIb bioimaging. The downshifting emission beyond 1500 nm is improved by 1.75−2.2 times with simultaneously suppressing the upconversion (UC) path in Y, Yb, and Lu hosts via Ce 3+ doping. Moreover, compared with the traditionally used Ybased host, the QY of NIR-IIb emission in the Lu-based probe in water is improved from 2.2% to 3.6%. The explored bright NIR-IIb emitted PAA-Lu-NRs were used for high sensitivity small tumor (∼4 mm)/metastatic tiny tumor detection (∼3 mm), tumor vessel visualization with high spatial resolution (41 μm), and brain vessel imaging. Therefore, our findings open up the opportunity of utilizing the lanthanide based NIR-IIb probe with bright 1525 nm emission for in vivo optical-guided tumor vessel/metastasis and noninvasive brain vascular imaging.

Carbon dots (CDs) with low biotoxicity, high photostability, and wellcontrolled size are highly desirable imaging agents for optical bioimaging. However, most of the CDs triggered by ultraviolet/blue light present visible/first near-infrared emissions shorter than 820 nm, impairing their imaging applications in vivo by low penetration depth. Hence, developing novel CD-based materials with second nearinfrared (NIR-II) emission located in 1000−1700 nm region is an urgent task. Here, a novel NIR-II-emitting CD-based nanoprobe triggered by 808 nm laser is developed. The designed CDs with 900−1200 nm luminescence possess high quantum yield (QY-0.4%) and high biocompatibility, which have proven to be effective probes for in vivo NIR-II bioimaging. Notably, nearly 65% CDs are excreted from mouse urine within 6 h, demonstrating the rapid renal clearance of CDs. Furthermore, the designed CDs also exhibit high photothermal efficiency (30.6%), making them ideal materials for thermal ablation of cancer. Our findings pave the way of designing a multifunctional CD-based theranostic platform for simultaneously integrating the advanced NIR-II bioimaging and photothermal therapy of cancer.

A strategy is demonstrated for simultaneous phase/size manipulation, multicolor tuning, and remarkably enhanced upconversion luminescence (UCL), particularly in red emission bands in fi xed formulae of general lanthanidedoped upconverting nanoparticles (UCNPs), namely NaLnF 4 :Yb/Er (Ln: Lu, Gd, Yb), simply through transition metal Mn 2+ -doping. The addition of different Mn 2+ dopant contents in NaLnF 4 :Yb/Er system favors the crystal structure changing from hexagonal (β) phase to cubic (α) phase, and the crystal size of UCNPs can be effectively controlled. Moreover, the UCL can be tuned from green through yellow and to dominant red emissions under the excitation of 980 nm laser. Interestingly, a large enhancement in overall UCL spectra of Mn 2+ doped UCNPs (∼59.1 times for NaLuF 4 host, ∼39.3 times for NaYbF 4 host compared to the UCNPs without Mn 2+ doping) is observed, mainly due to remarkably enhanced luminescence in the red band. The obtained result greatly benefi ts in vitro and in vivo upconversion bioimaging with highly sensitive and deeper tissue penetration. To prove the application, a select sample of nanocrystal is used as an optical probe for in vitro cell and in vivo bioimaging to verify the merits of high contrast, deeper tissue penetration, and the absence of autofl uorescence. Furthermore, the blood vessel of lung of a nude mouse with the injection of Mn 2+ -doped NaLuF 4 : Yb/ Er UCNPs can be readily visualized using X-ray imaging. Therefore, the Mn 2+ doping method provides a new strategy for phase/size control, multicolor tuning, and remarkable enhancement of UCL dominated by red emission, which will impact on the fi eld of bioimaging based on UCNP nanoprobes.