Stable solid-state red fluorescence from organosilane-functionalized carbon dots (CDs) with sizes around 3 nm is reported for the first time. Meanwhile, a novel method is also first reported for the efficient construction of dual-fluorescence morphologies. The quantum yield of these solid-state CDs and their aqueous solution is 9.60 and 50.7%, respectively. The fluorescence lifetime is 4.82 ns for solid-state CDs, and 15.57 ns for their aqueous solution. These CDs are detailedly studied how they can exhibit obvious photoluminescence overcoming the self-quenching in solid state. Luminescent materials are constructed with dual fluorescence based on as-prepared single emissive CDs (red emission) and nonfluorescence media (starch, Al O , and RnOCH COONa), with the characteristic peaks located at nearly 440 and 600 nm. Tunable photoluminescence can be successfully achieved by tuning the mass ratio of CDs to solid matrix (such as starch). These constructed dual-fluorescence CDs/starch composites can also be applied in white light-emitting diodes with UV chips (395 nm), and oxygen sensing.

photophysical properties that are potentially useful for different applications. [1-5] One of the many fascinating properties of CDs is its fluorescence. Many reports have shown that the fluorescence of CDs originates from the surface fluorophore and graphitizing core. [6-9] However, the transition between singlet and triplet states occurs with extremely low probability due to the spin-forbidden, hence the room temperature phosphorescence (RTP, T 1 →S 0) and thermally activated delayed fluorescence (TADF, transitions T 1 →S 1 →S 0) are difficult to be achieved under ambient conditions. [10-12] Other than that, afterglow from pure CDs is seldom observed and studied. [13-17] A selfquenching resistance CDs with RTP lifetime of 13.4 ms were induced by polyvinyl alcohol (PVA) chains from Liu's group. [13] Through seeded growth method, Andrey et al. prepared several phosphorescent CDs powders with average decay lifetime ranging from 52 to 419 ms. [14] Yang's group focused on suppressing the nonradiative transitions having achieved the adjustable decays between 188 and 658 ms. [15] Feng and co-workers found that fluorine and nitrogen codoped CDs with RTP could realize the decay lifetime of 141 to 1210 ms by adjusting pH values. [16] It is noteworthy that long-lived emission (LLE) about 1.46 s of CDs powder was successfully achieved via microwave irradiation but with very poor ability to resist moisture that RTP totally disappeared in solution and also quite faint emission intensity only with quantum yield (QY) of 3.53% by Lin et al. [17] As for these pure CDs, phosphorescence that is responsible for the total afterglow without TADF component only lasts for a few seconds accompanied by a relatively low phosphorescent efficiency. Furthermore, these pure CDs have extremely poor stability, thus afterglow of them was completely quenched by oxygen or moisture, causing the RTP to be only captured in powdery CDs rather than solution. [13-17] Nevertheless, a great deal of effort was devoted to improving the afterglow behavior. In some cases, the RTP can be ameliorated by introducing heavy atoms, such as halogens and metals which enhanced the intersystem crossing (ISC) process attributed to the strong spin-orbit coupling. [18,19] Alternatively, embedding CDs in solid matrices that serve Carbon nanodots (CDs) anchored onto inorganic supporter (amorphous nanosilica, SiO 2) like a core-satellite structure have enhanced the room-temperature phosphorescence (RTP) intensity along with ultralong lifetime of 1.76 s. Special and quite stable structure should account for these superiorities, including hydrogen network, covalent bond, and trap-stabilized triplet-state excitons that are responsible for the generation of phosphorescence. These multiple effects have efficaciously protected CDs from being restrained by the external environment, providing such long-lived emission (LLE) that can subsist not only in powdery CDs-SiO 2 but also coexist in aqueous solution, pushing a big step forward in the application prospects of liquid-state phosp...

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Double carbon dot-based fluorescent materials synthesised in one step possess dual characteristic peaks and multifunctional applications in WLED and transparent sunlight conversion film.

Positron annihilation lifetime spectra of MCM-41 and zeolite Y were measured at different vacuum levels. When the experiments were carried out in air, a very long lifetime component (τ4 = 35-45 ns, I4 = 15-20%) was observed for MCM-41, while the longest lifetime for zeolite Y was only 2-4 ns with an intensity of 15-25%. However, when the experiments were carried out in vacuum, the very long lifetime components could be observed for both samples, although with different intensities, ~30% for MCM-41 and ~10% for zeolite Y. For MCM-41 in air, the longest lifetime (τ4) is ~42 ns, corresponding to the ortho-positronium (o-Ps) annihilation lifetime in MCM-41 cavities. This value is slightly longer but very close to the value of 39 ns, which was estimated by using a bouncing quantum particle model. These peculiar positron annihilation characteristics were explained by air quenching mechanism of o-Ps annihilation in MCM-41. It was suggested that because of the existence of the very long lifetime component even in air, positron lifetime spectroscopy could be a very useful tool for nondestructive measurement of the cavity size of mesoporous solids such as MCM-41.