Energy storage systems including supercapacitors and lithium ion batteries typically appear in a rigid plate which is unfavorable for many applications, especially in the fi elds of portable and highly integrated equipments which require small size, light weight, and high fl exibility. [1][2][3] As a result, fl exible supercapacitors and batteries mainly in a fi lm format have been widely investigated, while wire-shaped energy storage devices are rare. [ 4 , 5 ] However, compared with the conventional planar structure, a wire device can be easily woven into textiles or other structures to exhibit unique and promising applications. The limitation is originated from the much stricter requirement for the electrode such as a combined high fl exibility and electrochemical property in wire-shaped devices. [ 6 , 7 ] It remains challenging but becomes highly desired to obtain wire-shaped supercapacitors and batteries with high performances.On the other hand, due to the unique structure and remarkable mechanical and electrical properties, carbon nanotubes (CNTs) have been widely studied as electrode materials in conventional planar energy storage devices. [ 8 , 9 ] However, CNTs are generally made in a network format in which the produced charges had to cross a lot of boundaries with low effi ciencies. It is critically important to improve the charge transport in CNT materials. [8][9][10][11][12][13] Herein, we have developed wire-shaped micro-supercapacitors and micro-batteries with high performances by using aligned multi-walled carbon nanotube (MWCNT) fi bers as electrodes. The micro-supercapacitor wire was fabricated by twisting two aligned MWCNT fi bers and showed a mass specifi c capacitance of 13.31 F/g, area specifi c capacitance of 3.01 mF/cm 2 , or length specifi c capacitance of 0.015 mF/cm at 2 × 10 − 3 mA (1.67 A/g). The wire-shaped battery was produced by twisting an aligned MWCNT fi ber and a lithium wire which functioned as positive and negative electrodes, respectively. The specifi c capacity was calculated as 94.37 mAh/cm 3 or 174.40 mAh/g at 2 × 10 − 3 mA. The energy and power densities in both supercapacitors and batteries could be further greatly improved by incorporation of MnO 2 nanoparticles into MWCNT fi bers. For instance, the charge and discharge energy densities achieved 92.84 and 35.74 mWh/cm 3 while the charge and discharge power densities were 3.87 and 2.43 W/cm 3 at 2 × 10 − 3 mA in the wire-shaped micro-battery.Spinnable MWCNT arrays were fi rst synthesized by chemical vapor deposition, and aligned MWCNT fi bers could then be spun from the array with controlled diameters from 2 to 30 μ m and lengths up to 100 m. Figure S1a shows a typical scanning electron microscopy (SEM) image of MWCNT fi ber with uniform diameter of 20 μ m. Figure 1 a further shows that MWCNTs are highly aligned in the fi ber, which enables high tensile strengths up to 1.3 GPa and high electrical conductivities of 10 3 S/cm. Therefore, the MWCNT fi bers had been further used as electrodes to deposit MnO 2 on the MWCN...

Upconversion is a nonlinear optical phenomenon that involves the emission of high‐energy photons by sequential absorption of two or more low‐energy excitation photons. Due to their excellent physiochemical properties such as deep penetration depth, little damage to samples, and high chemical stability, upconversion nanoparticles (UCNPs) are extensively applied in bioimaging, biosensing, theranostic, and photochemical reactions. Here, recent achievements in the synthesis, optimization, and applications of UCNP‐based nanomaterials are reviewed. The state‐of‐the‐art approaches to synthesize UCNPs in the past few years are introduced first, followed by a summary of several strategies to optimize upconversion emissive properties and various applications of UCNPs. Lastly, the challenges and future perspectives of UCNPs are provided as a conclusion.

Photodynamic therapy (PDT) has been considered as a promising and noninvasive strategy for clinical cancer treatment. Nonetheless, building a smart “off–on” theranostic PDT platform to spatiotemporally control the generation of reactive oxygen species in the PDT treatment still remains challenging. Here, we have rationally developed photoswitching upconversion nanoparticles (UCNPs) with orthogonal emissive properties in response to two distinct near-infrared (NIR) emissions at 808 and 980 nm, i.e., red emission with 980 nm excitation and green emission with 808 nm excitation. Unlike traditional photoswitching UCNPs, these specially designed core–shell–shell structured UCNPs do not require complicated multilayer doping as their red and green upconversion luminescence both originate from the same activator Er3+ ions in the core structure. As a proof of concept, we have demonstrated the capability of these orthogonal emissive UCNPs for imaging-guided PDT in a real-time manner, where the red emission excited by 980 nm light is used to trigger PDT and the green emission with 808 nm excitation is to diagnose and monitor the therapeutic treatment. Our study suggests that such specially designed UCNPs with orthogonal emissions hold great promise for NIR light-targeted and imaging-guided therapy under precisely spatiotemporal control.

Upconversion nanoparticles (UCNPs) represent a class of optical nanomaterials that can convert low-energy excitation photons to high-energy fluorescence emissions. On the basis of UCNPs, heterostructured UCNPs, consisting of UCNPs and other functional counterparts (metals, semiconductors, polymers, etc.), present an intriguing system in which the physicochemical properties are largely influenced by the entire assembled particle and also by the morphology, dimension, and composition of each individual component. As multicomponent nanomaterials, heterostructured UCNPs can overcome challenges associated with a single component and exhibit bifunctional or multifunctional properties, which can further expand their applications in bioimaging, biodetection, and phototherapy. In this review, we provide a summary of recent achievements in the field of heterostructured UCNPs in the aspects of construction strategies, synthetic approaches, and types of heterostructured UCNPs. This review also summarizes the trends in biomedical applications of heterostructured UCNPs and discusses the challenges and potential solutions in this field.

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