Semiconductor nanocrystals (SNCs) doped with Mn2+ and Cu2+ ions (ZnSe:Mn, ZnSe:Mn/CdSe, and ZnSe:Cu) were synthesized and their nonlinear absorption properties were investigated using the typical open-aperture Z-scan technique. A reversal from reverse saturable absorption (RSA) to saturable absorption (SA) was observed in the ZnSe:Mn SNCs. In contrast, the SA signals were largely suppressed and only RSA signals were measured in the ZnSe:Mn/CdSe and ZnSe:Cu SNCs. These different nonlinear absorption properties implied strong interactions between the excited excitons and impurity ions, which agreed well with the analysis performed by the theory model of the exciton transition in the energy structures. The nonlinearities of the doped SNCs could be controllably tuned by the integration of different doped ions and host SNCs. This strategy shows promise for extensive potential applications in optical limiting and switching.
Boxcar integrator and lock-in amplifier for the detecting of optical small signals are developed based on the virtual instrument technology of LabView.The algorithm of boxcar integrator is simple and easy-achieved.Lock-in amplifier is a powerful technique for the extracting and amplification of small signals.However, the cost of lock-in amplifier hardware is high.We develop digital boxcar integrator and lock-in amplifier in LabView platform.The performances of these two virtual measurement systems for optical small signal are exhibited and analyzed.
Doping with intentional impurities is an intriguing way to tune the properties of semiconductor nanocrystals. However, the synthesis of some specific doped semiconductor nanocrystals remains a challenge and the doping mechanism in this strongly confined system is still not clearly understood. In this work, we report, for the first time, the synthesis of stable and water-soluble Ag-doped CdTe semiconductor quantum dots (SQDs) via a facile aqueous approach. Experimental characterization demonstrated the efficient doping of the Ag impurities into the CdTe SQDs with an appropriate reaction time. By doping 0.3% Ag impurities, the Stokes shift is decreased by 120 meV, the fluorescence intensity is enhanced more than 3 times, the radiative rate is enhanced 4.2 times, and the non-radiative rate is efficiently suppressed. These observations reveal that the fluorescence enhancement in Ag-doped CdTe SQDs is mainly attributed to the minimization of surface defects, filling of the trap states, and the enhancement of the radiative rate by the silver dopants. Our results suggest that the silver doping is an efficient method for tuning the optical properties of the CdTe SQDs.
Abstract Excitation-dependent fluorophores (EDFs) have been attracted increasing attention owing to their high tunability of emissions and prospective applications ranging from multicolor patterning to bio-imaging. Here, we report tunable fluorescence with quenching dip induced by strong coupling of exciton and plasmon in the hybrid nanostructure of CTAB* EDFs and gold nanoparticles (AuNPs). The quenching dip in the fluorescence spectrum is tuned by adjusting excitation wavelength as well as plasmon resonance and concentration of AuNPs. The observed excitation-dependent emission spectra with quenching dip are theoretically reproduced and revealed to be induced by resonant energy transfer from multilevel EDFs with wider width channels to plasmonic AuNPs. These findings provide a new approach to prepare EDF molecules and a strategy to modulate fluorescence spectrum via exciton-to-plasmon energy transfer.
Upconversion materials have been employed as energy relay materials in dye sensitized solar cells (DSCs) to broaden the range of light absorption. However, the origin of the enhancements can be induced by both upconversion and size-dependent light scattering effects. To clarify the role of the upconversion material in the photoelectrode of DSCs, an upconversion induced device was realized here, which has the size-dependent light scattering effect eliminated via the application of NaYF4:Er(3+), Yb(3+)@SiO2 upconversion nanoparticles (β-NYEY@SiO2 UCNPs). An enhancement of 6% in efficiency was observed for the device. This demonstration provided an insight into the possible further employment of upconversion in DSCs.
The Au–Ag core–shell nanorods with asymmetric transverse cross section are synthesized, and their tunable linear and nonlinear optical responses are investigated. After the overgrowth of the asymmetric Ag shell on the Au nanorods, (i) a strong transverse octupole (TO) plasmon resonance at 390 nm is observed; (ii) the nonlinear refractive index γ at the TO resonance wavelength significantly increases from −0.15 × 10–4 to −0.85 × 10–4 cm2/GW, and the γ at the longitudinal dipole (LD) resonance wavelength slightly increases from −0.42 × 10–4 to −0.58 × 10–4 cm2/GW; (iii) but the nonlinear absorption coefficient β induced by the TO resonance is approximately 1 order of magnitude smaller than the one induced by the LD resonance. Consequently, the asymmetric Au–Ag core–shell nanorods at the TO resonance wavelength demonstrate a very large nonlinear refractive index as well as excellent nonlinear figures of merit (W = 4.4 > 1 and T = 0.14 < 1), which satisfy the demands for waveguide all-optical switching.
A common symptom of the blanket coverage of Western literary theory was the way Chinese intellectuals “kept harping on Greece,” to the neglect of their own literature’s distinctive features. Even worse were attempts to force Chinese literature into the Procrustean bed of Western literary propositions. How can Chinese literary theory be used more effectively to interpret native literature and culture, or Chinese experience? How can it throw off Western theoretical models and become a component of the Chinese nation’s own narrative? Reconstruction of the discourse system of Chinese literary theory must be a high priority. It is a complex project, one that necessarily entails stepping on to the discourse platform of modernity, accepting various kinds of open dialogue, and thence envisioning a new form of discourse system set amid multilayered overlapping perspectives and even the challenge of different ideas.
The theoretical dichotomy of the elegant (ya) and the popular or common (su) has a long history and many branches, provoking Babel-like confusion of tongues. Both have their own aesthetic origins, and each is interpreted in relation to sociological categories such as social class and social strata. No abstract and absolute definition of the two concepts exists. The yayue (formal ceremonial music) of ancient China is an important early example of the elegant or refined, whereas the popular usually prevails at the lower levels of mass society. In the course of history, the accumulation of professional knowledge, selected classics, avant garde “art for art’s sake,” and leisure class activities have often been considered “elegant,” while the experience of the masses, folk revelry, and the content of mass media have been considered “popular.” In modern literary history, the concepts of enlightenment and class were drawn into the dichotomy of the elegant and the popular in different ways. In Chinese culture in the second half of the twentieth century, this dichotomy began to be reorganized around the notions of “art” and “commodity.” The reconceptualization of elegance and popularity at each stage of history has often indicated a reconnection between aesthetic tastes and history. In this sense, the differentiation of elegance and popularity has always testified to culture’s participation in history.
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