No abstract

Surface‐enhanced Raman scattering (SERS) is a new optical spectroscopic analysis technique with potential for highly sensitive detection of molecules. Recently, many efforts have been made to find SERS substrates with high sensitivity and reproducibility. In this Research News article, we provide a focused review on the synthesis of monodispersed silver particles with a novel, highly roughened, “flower‐like” morphology by reducing silver nitrate with ascorbic acid in aqueous solutions. The nanometer‐scale surface roughness of the particles can provide several hot spots on a single particle, which significantly increases SERS enhancement. The incident polarization‐dependent SERS of individual particles is also studied. Although the different “hot spots” on a single particle can have a strong polarization dependency, the total Raman signals from an individual particle usually have no obvious polarization dependency. Moreover, these flower‐like silver particles can be measured by SERS with high enhancement several times, which indicates the high stability of the hot spots. Hence, the flower‐like silver particles here can serve as highly sensitive and reproducible SERS substrates.

displays. [1,2] In particular, perovskite-based light-emitting diodes (PeLEDs) with superior external quantum efficiency (EQE) and luminance have been demonstrated in the green, red, and near-infrared emission regions. [3][4][5][6] As display technologies continue to improve, the requirements for the emitters in the display become more stringent. As of August 2012, the Rec. 2020 standard defines the display color gamut for ultrahigh definition television (UHDTV): it requires each of the primary red, green, blue (RGB) emitters to have a precisely defined wavelength (red: 630 nm, green: 532 nm, and blue: 467 nm) and a narrow emission linewidth (<20 nm). [7] In state-of-art liquid crystal display backlights, crosstalk between color filters reduces the color purity of the RGB primaries. [8] LED displays do not require color filters and as such are promising candidate for UHDTV. Organic molecules have had success in commercial LED displays, but the wide linewidths (>50 nm) of organic emitters limit the attainable color gamut. [9] Developing emitters with precisely defined emission profiles for displays is an active Perovskite-based light-emitting diodes (PeLEDs) are now approaching the upper limits of external quantum efficiency (EQE); however, their application is currently limited by reliance on lead and by inadequate color purity. The Rec. 2020 requires Commission Internationale de l'Eclairage coordinates of (0.708, 0.292) for red emitters, but present-day perovskite devices only achieve (0.71, 0.28). Here, lead-free PeLEDs are reported with color coordinates of (0.706, 0.294)-the highest purity reported among red PeLEDs. The variation of the emission spectrum is also evaluated as a function of temperature and applied potential, finding that emission redshifts by <3 nm under low temperature and by <0.3 nm V −1 with operating voltage. The prominent oxidation pathway of Sn is identified and this is suppressed with the aid of H 3 PO 2 . This strategy prevents the oxidation of the constituent precursors, through both its moderate reducing properties and through its forming complexes with the perovskite that increase the energetic barrier toward Sn oxidation. The H 3 PO 2 additionally seeds crystal growth during film formation, improving film quality. PeLEDs are reported with an EQE of 0.3% and a brightness of 70 cd m −2 ; this is the record among reported red-emitting, lead-free PeLEDs.

High-yield uniform silver nanorices were synthesized by a facile polyol process without the introduction of shape-selected seeds. Nanorices exhibit two plasmon resonance peaks in the visible and near-infrared regions respectively due to their anisotropy. XRD patterns demonstrated the HCP phase coexists with the FCC phase in nanorices. The novel structure of nanorices was characterized by TEM study which shows that the intergrowth of FCC and a small amount of HCP phase, nanoscale FCC (111) twinning structure, and multimodulated structures formed by a complicated stacking sequence along the long axis direction. The correlation between morphology and microstructure is discussed.