Silicon
nanoparticles (Si NPs) exhibiting observable luminescence have many
electronic, optical, and biological applications. Owing to reduced
toxicity, they can be used as cheap and environmentally friendly alternatives
for cadmium containing quantum dots, organic dyes, and rare earth-based
expensive phosphors. Here, we report an inexpensive silicon precursor,
namely rice husk, which has been employed for the synthesis of Si
NPs by rapid microwave heating. The Si NPs of ∼4.9 nm diameter
exhibit observable green luminescence with a quantum yield of ∼60%.
They show robust storage stability and photostability and have constant
luminescence during long-term UV irradiation extending over 48 h,
in contrast to other luminescent materials such as quantum dots and
organic dyes which quenched their emission over this time window.
Green luminescent Si NPs upon mixing with synthesized red and blue
luminescent Si NP species are shown to be useful for energy-efficient
white light production. The resulting white light has a color coordinate
of (0.31, 0.27) which is close to that of pure white light (0.33,
0.33). The performance of our white light emitting material is comparable
to that of a commercial white light emitting diode (WLED) bulb and
is shown to be better than that of a commercial compact fluorescent
lamp (CFL).
Atomically precise noble metal nanoclusters protected with proteins have emerged as a new research frontier in nanoscience due to their unique optical and chemical properties as well as promising applications. In the present work, we have employed an ambient electrospray technique to synthesize proteinprotected luminescent clusters of gold and silver within the time scale of a few microseconds, which typically takes hours. In the absence of an electric field, the spray results in nanoparticles and no cluster formation was noticed. Synthesis of these clusters in microdroplets leads to severalfold enhancement in the rate of cluster formation. Spectroscopic investigations such as optical absorption, transmission electron microscopy, and matrix-assisted laser desorption ionization mass spectrometry confirm the molecular nature of the particles formed. Luminescence of electrospray-synthesized clusters shows multifold enhancement as compared to the clusters synthesized in the solution phase. Luminescence of the clusters synthesized in microdroplets increases with the distance traveled by the spray. The formation of clusters via electrospray affects the secondary structure of the protein, and its conformation is different from that of the parent protein. The Au@BSA cluster is utilized for in vitro imaging of retinoblastoma NCC-RbC-51 cells demonstrating a biological application of the resultant material. The absence of solvents and additional reagents enhances the sustainability of the method.
We demonstrate the
formation of a versatile
luminescent organo-inorganic layered hybrid material, composed of
bovine serum albumin (BSA)-protected Au30 clusters and
aminoclay sheets. X-ray diffraction revealed the intercalation of
Au30@BSA in the layered superstructure of aminoclay sheets.
Coulombic attraction of the clusters and the clay initiates the interaction,
and the appropriate size of the clusters allowed them to intercalate
within the lamellar aminoclay galleries. Electron microscopy measurements
confirmed the hierarchical structure of the material and also showed
the cluster-attached clay sheets. Zeta potential measurement and dynamic
light scattering probed the gradual formation of the ordered aggregates
in solution. The hybrid material could be stretched up to 300% without
fracture. The emergence of a new peak in the luminescence spectrum
was observed during the course of mechanical stretching. This peak
increased in intensity gradually with the degree of elongation or
strain of the material. A mechanochromic luminescence response was
further demonstrated with a writing experiment on a luminescent mat
of the material, made by electrospinning.
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