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In traditional solar cells, photogenerated energetic carriers (so-called hot carriers) rapidly relax to band edges via emission of phonons, prohibiting the extraction of their excess energy above the band gap. Quantum confined semiconductor nanocrystals, or quantum dots (QDs), were predicted to have long-lived hot carriers enabled by a phonon bottleneck, i.e. , the large inter-level spacings in QDs should result in inefficient phonon emissions. Here we study the effect of quantum confinement on hot carrier/exciton lifetime in lead halide perovskite nanocrystals. We synthesized a series of strongly confined CsPbBr 3 nanocrystals with edge lengths down to 2.6 nm, the smallest reported to date, and studied their hot exciton relaxation using ultrafast spectroscopy. We observed sub-ps hot exciton lifetimes in all the samples with edge lengths within 2.6-6.2 nm and thus the absence of a phonon bottleneck. Their well-resolved excitonic peaks allowed us to quantify hot carrier/exciton energy loss rates which increased with decreasing NC sizes. This behavior can be well reproduced by a nonadiabatic transition mechanism between excitonic states induced by coupling to surface ligands.

Recent years have seen the revived interests in the triplet states of polycyclic aromatic hydrocarbons (PAHs) due to their potential applications ranging from photon upconversion to photoredox catalysis. Because of their "dark" nature, these triplets have to be generated via triplet energy transfer (TET) from sensitizers. Traditional sensitization schemes introduce a sizable energy loss (ca. ≥ 0.5 eV) resulting from intersystem crossing (ISC) in sensitizers. Consequently, triplets of naphthalene (Nap), the most energetic PAH triplets (∼2.6 eV), have remained relatively underexplored because ultraviolet (UV) photons and wide-energy-gap sensitizers would be required for the sensitization. Here we show that Nap triplets can be efficiently generated using TET from quantum-confined CsPbBr 3 perovskite nanocrystals (NCs). Quantum confinement is essential to meet the energetics and electronic coupling requirements in TET. Because of the vanishingly small bright-dark states energy splitting in NCs, this sensitization process can take place at the limit of energy conservation, driven by visible photons.

The spectral properties of lead halide perovskite nanocrystals (NCs) can be engineered by tuning either their sizes via the quantum confinement effect or their compositions using anion and/or cation exchange. To date, the latter is more frequently adopted, primarily because of the ease of ion exchange for lead halide perovskites, making the quantum confinement effect seemingly redundant for perovskite NCs. Here we report that quantum confinement is required for triplet energy transfer (TET) from perovskite NCs to polycyclic aromatic hydrocarbons (PAHs). Static and transient spectroscopy measurements on CsPbBr 3 NC-pyrene hybrids showed that efficient TET occurred only for small-sized, quantum-confined CsPbBr 3 NCs. The influences of the size-dependent driving force and spectral overlap on the TET rate were found to be negligible. Instead, the TET rate scaled linearly with carrier probability density at the NC surface, consistent with a Dexter-type TET mechanism requiring wave function exchange between the NC donors and pyrene acceptors. Efficient TET funnels the excitation energy generated in strongly light-absorbing perovskite NCs into long-lived triplets in PAHs, which may find broad applications such as photon upconversion and photoredox catalysis.

Objective: To compare two primary culture methods of human nasal epithelial (HNE) in vitro, and explore a suitable method to be used in further study., Method: Achievement ratio and growth curve of primarily cultural HNE by tissue piece culture were compared to those by isolated cell culture. Shape and appearance were observed and cellular sources were identified to get preliminary bionomics of HNE., Result: The isolated cell culture method (87.5%) was shown to be superior to tissue piece culture method (83.33%) by comparing achievement ratios, but no statistical significance was found (P > 0.05). The growth curve of isolated cell culture was higher than that of tissue piece culture. All cultured cells were confirmed coming from epithelial cells by observing shape, appearance and dyeing cytokeratin., Conclusion: The isolated cell culture method is more suitable for primary culture due to its less promiscuity, faster proliferation, and more stable and reliable cell supply.

Objective: To observe the relation between dermatomyositis/polymyositis and head-neck malignancy., Method: All 136 cases of dermatomyositis/polymyositis admitted to PUMCH during 10 years (1994-2003) were studied. The clinical features of 6 patients with an associated head-neck malignancy were analyzed., Result: There were 17 cases of malignancy in 136 patients with dermatomyositis/polymyositis, of which, 6 cases (6/17, 35.29%) were found to have head-neck malignancy: 4 cases of nasopharyngeal carcinoma, 1 case of non-Hodgkin lymphoma and 1 case of hypopharynx carcinoma., Conclusion: Nasopharyngeal carcinoma represents the first neoplasm among head-neck malignancy associated with dermatomyositis/polymyositis. Nasal endoscopic and/or fibrolaryngoscopic search for potential head-neck malignancy should be performed in every patient with dermatomyositis/polymyositis.