Yb3+/Ln3+/Mn4+ (Ln = Er, Ho, and Tm) doped Na3ZrF7 phosphors: oil–water interface cation exchange synthesis, dual-modal luminescence and anti-counterfeiting

Abstract

Efficient dual-modal luminescence is highly desired for applications in high security anti-counterfeiting. In the present work, Yb³⁺/Ln³⁺/Mn⁴⁺ (Ln = Er, Ho, and Tm) tri-doped Na₃ZrF₇ phosphors were fabricated via oil–water interface cation exchange using Yb³⁺/Ln³⁺:Na₃ZrF₇ as the exchanging hosts. The as-prepared products exhibited typical Mn⁴⁺ red down-shifting luminescence under UV light excitation and Er³⁺ red, Ho³⁺ yellow and Tm³⁺ near-infrared multi-color upconversion emissions under 980 nm laser excitation. The Mn⁴⁺ dopants in the Na₃ZrF₇ host experienced strong crystal-field strength D_q of 3.63 and showed superior thermal stability with up to 90% of the initial emission intensity retained at 448 K. Steady-state and time-resolved emission spectra verified that there was no detrimental energy transfer interaction between Mn⁴⁺ and Ln³⁺, enabling bright and eye-visible bi-functional emissions for the present products. As a consequence, the as-prepared phosphors were demonstrated to be applicable in anti-counterfeiting by a proof of concept experiment of fluorescent labeling for specially designed patterns.