Rare-Earth Doping Graphitic Carbon Nitride Endows Distinctive Multiple Emissions with Large Stokes Shifts

Two-dimensional(2D)graphitic carbon nitride(g-C_(3)N_(4))possesses a unique geometric configuration featuring a superimposed heterocyclic sp2 carbon and nitrogen framework.Its fluorescence may be attributed to π-π^(*),lone pair(LP)-π^(*),or LP-δ^(*)transitions.So far,the manipulation of its fluorescence emissions is largely unexploited and remains challenging.Herein,for the first time,rare-earth doping into the backbone structure of a g-C_(3)N_(4) framework under microwave agitation endows unprecedented fluorescence nature,with the emergence of two exceptional new fluorescence emissions in the 450-700 nm range.With terbium-doped g-C_(3)N_(4):Tb as a representative,these emissions exhibit distinctive features,that is,very sharp fluorescence peaks with narrow full width at half maximum(FWHM)(peak width at half-height)of<12 nm,quantumyields of 2.3±0.0% and 7.6±0.1% for the new emissions at λ_(ex)/λ_(em)=290/490 nm,and 290/545 nm,respectively;and a large Stokes shift of>200 nm.These features of g-C_(3)N_(4):Tb are most advantageous for applications in various fields,as demonstrated by(1)tracking biodistribution of g-C_(3)N_(4) in vivo with mass spectrometric imaging where the doped terbium serves as a tag,(2)a biometrics study facilitating the identification of an individual through fingerprint,and(3)anti-counterfeiting with g-C_(3)N_(4)∶Tb as a dual-functional marker to facilitate fluorescence and mass spectrometric imaging.

Investigating fatigue behavior of gear components with the acoustic emission technique

A novel method is presented to evaluate the complicated fatigue behavior of gears made of20Cr2Ni4 A.Fatigue tests are conducted in a high-frequency push-pull fatigue tester,and acoustic emission（AE）technique is used to acquire metal fatigue signals.After analyzing large number of AE frequency spectrum,we find that：the crack extension can be expressed as the energy of specific frequency band,which is abbreviated as F-energy.To further validate the fatigue behavior,some correlation analysis is applied between F-energy and some AE parameters.Experimental results show that there is significant correlation among the Fenergy,root mean square（RMS）,relative energy,and hits.The findings can be used to validate the effectiveness of the F-energy in predicting fatigue crack propagation and remaining life for parts in-service.F-energy,as a new AE parameter,is first put forward in the area of fatigue crack growth.

Anisotropy in Third-Order Nonlinear Optical Susceptibility of a Squarylium Dye in a Nematic Liquid Crystal

A squarylium dye is dissolved in 4-cyano-4＇-pentylbiphenyl （SCB） and oriented by sandwiching mixtures between two pieces of rubbed glass plates. The optical absorption spectra of the oriented squarylium dye-5CB layers exhibit high anisotropy. The third-order nonlinear optical responses and susceptibilities X^（3）e of squarylium dye in 5CB are measured with light polarizations parallel and perpendicular to the orientational direction by the resonant femtosecond degenerate four-wave mixing （DFWM） technique. Temporal profiles of the DFWM signal of the oriented squarylium dye-5CB layers with light polarizations parallel and perpendicular to the orientational direction are measured with a time resolution of 0.3ps （FWHM）, and are found to consist of two components, i.e., the coherent instantaneous nonlinear response and slow response due to the formation of excited molecules. A high anisotropic ratio of x^（3）e, 10.8 ：k 1.2, is observed for the oriented layers.