多激发光窗口下银纳米颗粒表面等离激元增强多光子量子剪裁发光

通过高温固相法制备了NaBaPO_(4)∶Er^(3+)荧光材料。采用化学还原法制备银纳米颗粒(银球与银立方),并修饰到NaBaPO_(4)∶Er^(3+)荧光材料中形成复合材料。利用银纳米颗粒表面等离激元特性实现了多激发光窗口激发下NaBaPO_(4)∶Er^(3+)多光子近红外量子剪裁发光增强。实现了在377 nm与485 nm光激发下,银球纳米颗粒表面等离激元增强NaBaPO_(4)∶Er^(3+)四光子与三光子近红外发光;在519 nm光激发下,银立方纳米颗粒表面等离激元增强NaBaPO_(4)∶Er^(3+)三光子近红外发光。

Effect of substrate porosity on photoluminescence properties of ZnS films prepared on porous Si substrates by pulsed laser deposition

ZnS films were deposited on porous Si(PS) substrates with different porosities by pulsed laser deposition. The photolumi-nescence spectra of the samples were measured to study the effect of substrate porosity on luminescence properties of ZnS/porous Si composites. After deposition of ZnS films,the red photoluminescence peak of porous Si shows a slight blueshift compared with as-prepared porous Si samples. With an increase of the porosity,a green emission at about 550 nm was observed which may be ascribed to the defect-center luminescence of ZnS films,and the photoluminescence of ZnS/porous Si composites is very close to white light. Good crystal structures of the samples were observed by x-ray diffraction,showing that ZnS films were grown in preferred orientation. Due to the roughness of porous Si surface,some cracks appear in ZnS films,which could be seen from scanning electron microscope images.

Measurement of Photoionization Cross Sections of the Excited States of Titanium

Resonance-enhanced multiphoton ionization of the titanium atoms has been investigated in the 293 321 nm wavelength. We couple a laser-ablated metal target into a molecular beam to produce free atoms. Ions produced from photoionization of the neutral atoms are monitored by a home-built time-of-flight mass spectrometer. Photoionization cross sections of the excited states of Ti I were deduced from the dependence of the ion signal intensity on the laser intensity for photon energies close to the ionization threshold. The values obtained range from 0.2 Mb to 6.0 Mb. No significant isotope-dependence was found from measurements of the photoionization cross sections of ^46Ti, ^47Ti, and ^48Ti.

Photolumincscent Properties of Polyacetylenes Carbazole

The optical properties of one mono-substituted polyacetylene and two di-substituted polyacetylenes have been investigated. Each of the substituted polyacetylenes bears a carbazole unit in the side chain. In spite of the differences in their molecular structures, the dilute solutions(about 1×10-6 M) of these substituted polyacetylenes exhibit the same absorptions and deep-blue emissions(about 360 nm). Interestingly, the absorption and emission spectra of these substituted polyacetylenes are similar to those of the small molecule carbazole. As the concentration of the substituted polyacetylenes increases to about 1×10-6 M, we have detected intense blue emissions at about 475 nm. Our results indicate that the absorption, the deep-blue emission(about 360 nm) and the intense blue emission(about 475 nm) originate from the carbazole chromophores in the side chain.

Direct and Indirect Excitons in Two-Dimensional Covalent Organic Frameworks

Highly luminescent bulk two-dimensional covalent organic frameworks(COFs)attract much attention recently.Origin of their luminescence and their large Stokes shift is an open question.After first-principles calculations on two kinds of COFs using the GW method and Bethe-Salpeter equation,we find that monolayer COF has a direct band gap,while bulk COF is an indirect band-gap material.The calculated optical gap and optical absorption spectrum for the direct excitons of bulk COF agree with the experiment.However,the calculated energy of the indirect exciton,in which the photoelectron and the hole locate at the conduction band minimum and the valence band maximum of bulk COF respectively,is too low compared to the fluorescence spectrum in experiment.This may exclude the possible assistance of phonons in the luminescence of bulk COF.Luminescence of bulk COF might result from exciton recombination at the defects sites.The indirect band-gap character of bulk COF originates from its AA-stacked conformation.If the conformation is changed to the AB-stacked one,the band gap of COF becomes direct which may enhance the luminescence.

Development and Potential of Space-Borne Doppler Wind Lidar

The advantage of lidar over other wind sensors is presented in this paper. With more than 20 years research, the development of the space-borne wind lidar is reviewed. Longer-term investigation has made many technologies suitable for the wind lidar measurement from an orbital platform become mature. However, there are still some problems to be solved. In order to obtain the optimal performance in wind detection, great importance is being attached to the simulation of a virtual space-borne wind lidar system on computer as developed by NASA and ESA.

Reconstruction of Turbulent Swirling Flow in a Dump Combustor

Experimental data of the continuous evolution of fluid flow characteristics in a dump combustor is very useful and essential for better and optimum designs of gas turbine combustors and ramjet engines. Unfortunately, experimental techniques such as 2D and/or 3D LDV （Laser Doppler Velocimetry） measurements provide only limited discrete information at given points; especially, for the cases of complex flows such as dump combustor swirling flows. For this type of flows, usual numerical interpolating schemes appear to be unsuitable. Recently, neural networks have emerged as viable means of expanding a finite data set of experimental measurements to enhance better understanding of a particular complex phenomenon. This study showed that generalized feed forward network is suitable for the prediction of turbulent swirling flow characteristics in a model dump combustor. These techniques are proposed for optimum designs of dump combustors and ramjet engines.

Achieving mechano-upconversion-downshifting-afterglow multimodal luminescence in a lanthanide-doped LaCaAl_(3)O_(7) phosphor for multidimensional anticounterfeiting

The tunable excitation patterns and emission modes associated with luminescence materials,such as downshifting luminescence(DSL),upconversion luminescence(UCL),and mechanoluminescence(ML)play an important role in information encryption and anticounterfeiting.However,many reported luminescence materials usually show fixed excitation patterns and unimodal output,resulting in a low anticounterfeiting level.Therefore,developing luminescence materials with multitemporal,variation excitation patterns and multiple emission modes remains a considerable challenge,particularly in a single matrix.This study reports a highly integrated multifunctional material(color-tunable(DSL:amaranth→blue),tunable excitation patterns(250±380 nm)and quadrimodal(DSL,UCL,persistent luminescence(PersL),and ML)).The as-obtained versatile LaCaAl_(3)O_(7):Eu^(2+)/^(3+),Yb^(3+),Er^(3+)materials are suitable for obtaining elastomer films with the characteristics of water resistance,stretchability,and flexibility and synchronously offer multidimensional information encryptions and anticounterfeiting using common tools(ultraviolet light,nearinfrared light,and pen).These results provide a unique insight into advanced multimodal anticounterfeiting.