Publisher Correction: Tunable long persistent luminescence in the second near-infrared window via crystal field control.

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Tunable long persistent luminescence in the second near-infrared window via crystal field control.

Construction of an active composite as a biomarker with deeper tissue penetration and higher signal-to-noise ratio (SNR) is of great importance for the application in bioimaging. Here, we report a strategy for tuning the emission bandwidth and intensity via crystal field control in long persistent phosphors (LPPs). Ni2+-doped Zn1+ySnyGa2-x-2yO4 phosphors, with a tunable emission band peaking from 1270 to 1430 nm in the second near-infrared (NIR) window, have been successfully prepared. Such featured materials have the advantages of low absorption and scattering as well as more efficient tissue penetration. The emission spectra can be controlled by tailoring the local crystal field around the activator precisely via substitution of Zn and Sn for Ga. Moreover, with high resolution and weak light disturbance, these developed multi-band afterglow phosphors exhibit great application potential in advanced optical imaging.

A strategy for fabrication of controllable 3D pattern containing clusters and nanoparticles inside a solid material.

Directly controlling the growth process of clusters and nanoparticles is an effective way to tune their specific properties, which has been considered as a significant issue lying at the heart of nanotechnology. For technological applications, great strides have been made in the assembly of clusters and nanoparticles. However, controllable synthesis of clusters and nanoparticles inside a bulk solid-state medium remains a tremendous challenge, which is important for integrated devices. Here we report a strategy for space-selective control of elemental tellurium (Te) precipitation as clusters or nanoparticles in glass by femtosecond (fs) laser irradiation. After irradiation by a 1 kHz fs laser at 800 nm, Te2 clusters, which emit near-infrared (NIR) light, are observed at the focal point of the laser beam inside the glass sample. By shifting the repetition rate to 250 kHz, a temperature field forms around the focal area that facilitates transformation of Te clusters into nanoparticles. Raman mapping shows that the clusters are localized in the center of the laser-induced microstructure, while the nanoparticles exhibit an annular distribution. The possible mechanisms of generation and distribution of different species are discussed. We have also demonstrated optical data storage and embedded micro-grating by using this technique.

Controllable optical modulation of blue/green up-conversion fluorescence from Tm3+ (Er3+) single-doped glass ceramics upon two-step excitation of two-wavelengths.

Optical modulation is a crucial operation in photonics for network data processing with the aim to overcome information bottleneck in terms of speed, energy consumption, dispersion and cross-talking from conventional electronic interconnection approach. However, due to the weak interactions between photons, a facile physical approach is required to efficiently manipulate photon-photon interactions. Herein, we demonstrate that transparent glass ceramics containing LaF3: Tm3+ (Er3+) nanocrystals can enable fast-slow optical modulation of blue/green up-conversion fluorescence upon two-step excitation of two-wavelengths at telecom windows (0.8-1.8 µm). We show an optical modulation of more than 1500% (800%) of the green (blue) up-conversion fluorescence intensity, and fast response of 280 µs (367 µs) as well as slow response of 5.82 ms (618 µs) in the green (blue) up-conversion fluorescence signal, respectively. The success of manipulating laser at telecom windows for fast-slow optical modulation from rear-earth single-doped glass ceramics may find application in all-optical fiber telecommunication areas.

Enhanced nonlinear optical response of Se-doped MoS2 nanosheets for passively Q-switched fiber laser application.

An enhanced nonlinear optical (NLO) performance was observed in Se-doped MoS2 nanosheets synthesized through a facile annealing process. Se-doped MoS2 nanosheets with a large saturable intensity and high modulation depth generated stable passively Q-switched fiber laser pulses at 1559 nm. In comparison with the Q-switched fiber laser utilizing the pristine MoS2 nanosheets as a saturable absorber, the passive Q-switching operation based on Se-doped MoS2 nanosheets could be conducted at a lower threshold power of 50 mW, a wider range of repetition rates from 28.97 to 130 kHz, and a higher SNR of 56 dB. More importantly, the shortest pulse duration of 1.502 µs was realized and the output power and pulse energy reached 17.2 mW and 133.07 nJ, respectively. These results indicate that tailoring the chemical composition of optical nanomaterials by introducing a dopant is a feasible method of improving the NLO response of the MoS2 nanosheets and realizing excellent ultrafast pulse generation.

Vertically standing layered MoS2 nanosheets on TiO2 nanofibers for enhanced nonlinear optical property.

Vertical layered MoS2 nanosheets rooting into TiO2 nanofibers were successfully prepared by a facile two-step method: prefabrication of porous TiO2 nanofibers based on an electrospinning technique, and assembly of MoS2 ultrathin nanosheets through a simple hydrothermal reaction. Significant enhancement of nonlinear optical response of the MoS2/TiO2 nanocomposite was confirmed by an open-aperture z-scan measurement. The nanocomposite displayed strong optical limiting (OL) effects to ultrafast laser pulses with a low OL threshold of ~22.3 mJ/cm2, which is lower than that of pristine TiO2 nanofibers and MoS2 nanosheets. In addition to the contribution of the strong nonlinear absorption of MoS2 nanosheets and TiO2 nanofibers, such phenomenon is also attributed to the unique structure of vertically standing layered MoS2 nanosheets on TiO2 nanofibers with a large amount of exposed edge states, large surface areas and fast electron transfer between TiO2 and MoS2. This work broadens our vision to engineering novel hierarchical MoS2-based nanocomposite for efficiently enhanced nonlinear light-matter interaction.

Evolution of polarization dependent microstructures induced by high repetition rate femtosecond laser irradiation in glass.

We report the observation of an anomalous polarization dependent process in an isotropic glass induced by long time stationary irradiation of a high repetition rate near-infrared femtosecond laser. Two distinctive types of polarization dependent microstructures were induced at different irradiation stages. At early stage (a few seconds), a dumbbell-shaped structure elongated perpendicularly to the laser polarization formed at the top of the modified region, which was later erased by further irradiation. At later stage (above 30 s), bubbles filled with O2 formed by the irradiation, which were distributed along the laser polarization at a distance far beyond the radius of the laser beam. Based on a simple modeling of light reflection on boundaries, a thermal accumulation process was proposed to explain the formation and evolution of the dumbbell-shaped microstructure. The possible factors responsible for polarization dependent distribution of bubbles are discussed, which needs further systematic investigations. The results may be helpful in the development of femtosecond laser microprocessing for various applications.

Terpenoids from roots of Chloranthus henryi.

Six new terpenoids, including three diterpenoids (1-3), one norditerpenoid (4) and two sesquiterpenoids (11 and 12), were isolated from the roots of Chloranthus henryi. The structures were elucidated mainly by 1D, and 2D NMR and MS experiments, and their relative configurations were determined by NOE techniques.

Dammarane-type glycosides from Gynostemma pubescens.

Triterpene saponins 1-8 were isolated from the aerial parts of Gynostemma pubescens. Among them, compounds 1-4, 8 possess carboxylic groups at both C-21 and C-29, 5 contains a carboxylic group at C-21 and an aldehyde function at C-29, whereas 6 and 7 contain carboxylic groups at C-21 and hydroxymethylene groups at C-29. Their structural elucidation was accomplished by extensive spectroscopic methods including application of 1D (1H, (13)C, (13)C DEPT) and 2D NMR experiments (HMQC, HMBC, HSQC), HRESIMS analysis, as well as by chemical degradation.