Synthesis And Optical Property Of Ag Modified Of Tm³⁺ Doped12CaO·7Al₂O₃Nanocrystals

Tm³⁺-doped C12A7powders and Ag/C12A7:Tm³⁺were fabricated by the chemicalco-precipitation method. The X-ray diffraction （XRD）, field emission scanning electronmicroscopy （FE-SEM）, and transmission electron microscopy （TEM） were conducted toinvestigate the microstructure of the powders; Up-conversion emission spectrum,UV-Vis-NIR absorption spectra, fluorescence decay curve were analyzed to study their opticalproperties.The XRD study revealed that the cage structural polycrystalline12CaO·7Al₂O₃（C12A7）powders were obtained. It demonstrated that Tm³⁺had been doped into the host in situ. SEMshowed that C12A7:Tm³⁺powders with the grain size of200-400nm were synthesized. Thecrystal microstructure of the Ag NPs with grain size several nm was characterized by TEM.Up-conversion emission bands at367,457,476,528,551,648and682nmcorresponding, respectively, to the transitions¹D₂→³H₆,¹D₂→³F₄,¹G₄→³H₆,¹D₂→³H₅,¹G₄→³F₄, and3F3→³H₆were observed under excitation at808nm. Plasmon-enhancedultraviolet and blue up-conversion emissions in Tm³⁺-doped C12A7nanocrystals （NCs） wereachieved by attaching Ag nanoparticles （NPs） onto the up-conversion NCs surface. Theemission enhancement by Ag NPs is highly wavelength-dependent and the maximumamplifications of the367and478nm emissions are10and3folds, respectively at Ag+concentration of5.0×10^-3mol/L. The Tm³⁺-doped C12A7NCs with Ag NCs attachmentdisplay well-defined broad plasmon absorption band peaked at420nm around, whichoverlaps well with the two major emission bands in the up-conversion NCs （367and476nm）.It suggests that SPCE plays a role in the ultra-giant enhancement of up-conversion emissionsof Tm³⁺. The lifetime measurement clearly shows that the fluorescence decay of theupconversion NCs with Ag NPs （average lifetime1.01and11.47μs） is faster than that of theupconversion NCs only （average lifetime1.30and20.30μs）. It suggests that SPCE plays arole in the ultra-giant enhancement. The local field enhancement （LFE） plays a role in theultra-giant enhancement of up-conversion emissions of Tm³⁺according to the analysis. Theresonance energy of the surface-plasmons （SPs） at the Ag/C12A7interface was calculated toclarify the wavelength-dependent mechanism.