Engineering tri-channel orthogonal luminescence in a single nanoparticle for information encryption

Abstract

Optical anti-counterfeiting technology based on the multicolor emission generated by the abundant energy levels of rare earth ions shows great potential in the face of increasing information security problems worldwide. However, it is not an easy task to achieve multi-channel orthogonal emissions in a single nanoparticle with a simple structure by a convenient method. In this work, we have successfully realized the tri-channel orthogonal emissions under three excitation wavelengths in NaErF₄@NaYF₄:Eu³⁺@NaBiF₄:Yb³⁺,Tm³⁺ core@shell@shell nanoparticles. In our design, the interlayer NaYF₄:Eu³⁺ plays the role of “one arrow aiming at three eagles”. First, it can enhance the upconversion luminescence intensity of NaErF₄. Next, it makes the emission color of Er³⁺ change from red to green by the energy transfer process between Er³⁺ and Eu³⁺. Finally, it can produce red emission under 395 nm light excitation. This selective excitation strategy enables R-G-B tri-channel orthogonal emissions in a single nanoparticle by simply changing the excitation wavelength, which is very suitable for high level optical information encryption. This work provides a simple and effective method for the design of smart luminescent materials, showing great potential for multi-level anti-counterfeiting and information security.