Engineering Orthogonal Upconversion through Selective Excitation in a Single Nanoparticle

Orthogonal upconversion with color-switchable emissions under different excitation conditions provides new chances to diverse frontier applications of luminescent materials. However, the previous orthogonal upconversion systems compulsorily require the precise control of spatial distributions of dopants and host compositions to avoid spectral cross-talk, greatly limiting their synthesis and application. Herein, a conceptual design is presented to realize the orthogonal upconversion by selectively activating sensitizers and activators in nanostructure. In detail, the 915 nm laser, instead of the mostly used 980 nm, is adopted to activate the sensitizer Yb3+ because of the broad F-2(5/2)<- F-2(7/2) absorption band; while it is non-responsive to Er3+, consequently avoiding the spectral cross-talk due to the simultaneous activation of both Er3+ and Yb3+ under 980 nm irradiation as shown in the previous works. Such a selective excitation strategy is able to realize the red/green, blue/red, and blue/green orthogonal upconversion in a single nanoparticle by simply altering the excitation wavelength from 915 to 1530 nm. More interestingly, it further allows for full-color output by temporal control of the upconversion dynamics. The findings suggest a facile but effective approach to the design of smart luminescent materials, showing great potential in multi-level anti-counterfeiting, information security and biological applications.