Ding Zhou

Recently high doping of lanthanide ions (till 100 %) is realized unprecedentedly in nanostructured upconversion (UC) phosphors. However, oddly enough, this significant breakthrough did not result in a corresponding UC enhancement at ambient temperature, which hinders the otherwise very interesting applications of these materials in various fields. In this work, taking the Er³⁺‐rich UC nanosystem as an example, we confirm unambiguously that the phonon‐assisted cross relaxation (CR) is the culprit. More importantly, combining the theoretical modeling and experiments, the precise roles of different CR channels on UC energy loss are quantitatively revealed. As a result, lowering the temperature can exponentially enhance the relevant UC luminescence by more than two orders of magnitude. Our comprehension will play an important role in promoting the UC performance and further application of high doping rare earth materials. As a proof of concept, an Er³⁺‐rich core/multi‐shell nanophosphor is exploited which demonstrates the great potential of our finding in the field of ultra‐sensitive temperature sensing.

Recently high doping of lanthanide ions (till 100 %) is realized unprecedentedly in nanostructured upconversion (UC) phosphors. However, oddly enough, this significant breakthrough did not result in a corresponding UC enhancement at ambient temperature, which hinders the otherwise very interesting applications of these materials in various fields. In this work, taking the Er³⁺‐rich UC nanosystem as an example, we confirm unambiguously that the phonon‐assisted cross relaxation (CR) is the culprit. More importantly, combining the theoretical modeling and experiments, the precise roles of different CR channels on UC energy loss are quantitatively revealed. As a result, lowering the temperature can exponentially enhance the relevant UC luminescence by more than two orders of magnitude. Our comprehension will play an important role in promoting the UC performance and further application of high doping rare earth materials. As a proof of concept, an Er³⁺‐rich core/multi‐shell nanophosphor is exploited which demonstrates the great potential of our finding in the field of ultra‐sensitive temperature sensing.

Relatively low efficiency is the bottleneck for the application of lanthanide‐doped upconversion nanoparticles (UCNPs). The high‐level doping strategy realized in recent years has not improved the efficiency as much as expected. It is argued that cross relaxation (CR) is not detrimental to upconversion. Here we combine theoretical simulation and spectroscopy to elucidate the role of CR in upconversion process of Er³⁺ highly doped (HD) UCNPs. It is found that if CR is purposively suppressed, upconversion efficiency can be significantly improved. Specifically, we demonstrate experimentally that inhibition of CR by introducing cryogenic environment (40 K) enhances upconversion emission by more than two orders of magnitude. This work not only elucidates the nature of CR and its non‐negligible adverse effects, but also provides a new perspective for improving upconversion efficiency. The result can be directly applied to cryogenic imaging and wide range temperature sensing.

Relatively low efficiency is the bottleneck for the application of lanthanide‐doped upconversion nanoparticles (UCNPs). The high‐level doping strategy realized in recent years has not improved the efficiency as much as expected. It is argued that cross relaxation (CR) is not detrimental to upconversion. Here we combine theoretical simulation and spectroscopy to elucidate the role of CR in upconversion process of Er³⁺ highly doped (HD) UCNPs. It is found that if CR is purposively suppressed, upconversion efficiency can be significantly improved. Specifically, we demonstrate experimentally that inhibition of CR by introducing cryogenic environment (40 K) enhances upconversion emission by more than two orders of magnitude. This work not only elucidates the nature of CR and its non‐negligible adverse effects, but also provides a new perspective for improving upconversion efficiency. The result can be directly applied to cryogenic imaging and wide range temperature sensing.

Skin lesions, as a relatively common clinical manifestation, not only damage the skin's barrier function, but also affect the skin's ability to feel temperature, pain and touch. However, a highly efficient method to restore the morphology and function of damaged skin remains an unmet goal. In this work, carbon dots (CDots) with excellent biocompatibility are synthesized via microwave‐assisted heating ascorbic acid and polyethyleneimine. The synthesized CDots can induce the epithelial‐mesenchymal transition (EMT) process by activating transforming growth factor‐β/p‐38 mitogen‐activated kinase/Snail signaling pathway, leading to an increase of cell motility. Further, by assessing a series of in vivo wound healing assays and histological examinations, it is demonstrated that CDots can accelerate the migration of epithelial cells in the full‐thickness cutaneous wounds through EMT. As a result, a rapid re‐epithelialization covers the granulation tissue and epidermal barrier formed, leading to a block of the external stimuli, reduction of the inflammatory reaction and the granulation tissue area, and finally the promotion of the wound healing with fewer scars.

Gene therapy is one of the most common and effective ways for the regeneration of defective bone tissue, but even highly efficient gene delivery vectors are insufficient. In this study, bone morphogenetic protein-2 plasmid (pBMP-2) was encapsulated by polyethylenimine-modified porous silica nanoparticles (PPSNs), which were synthesized via an ethyl ether emulsion method. Owing to the high specific surface area and high absorption characteristics, low cytotoxicy PPSNs can efficiently load and protect pBMP-2. The resulting PPSN/pBMP-2 can transfect MC3T3-E1 cells effectively to promote osteogenic differentiation and increase calcium deposition in vitro. Interestingly, the mass of calcium deposition nodules decreased dur to the presence of an autophagy inhibitor, demonstrating that PPSNs stimulated the autophagy pathway. Because of their excellent biocompatibility, high transfection efficiency, and ability to stimulate autophagy, the as-prepared PPSN/pBMP-2 could efficiently transfect local cells in a defect area in vivo. Micro-computed tomography and histological images demonstrated that PPSN/pBMP-2 could efficiently promote new bone formation in a 5 mm sized rat calvarial defect model. Taken together, our newly synthesized PPSNs could efficiently carry pBMP-2 and deliver it to the target cells as well as stimulating the autophagy pathway, resulting in significant osteogenic differentiation and bone regeneration.