Cryogenic enabled multicolor upconversion luminescence of KLa(MoO₄)₂:Yb³⁺/Ho³⁺ for dual-mode anti-counterfeiting

The rational development of multicolor upconversion (UC) luminescent materials is particularly promising for achieving high-tech anti-counterfeiting and security applications. Here, an Ho³⁺ and Yb³⁺ ion co-doped KLa(MoO₄)₂ material can achieve multicolored UC luminescence by thermally manipulating the electron transition process, which could be developed to execute advanced optical anti-counterfeiting applications. The emission color of this material turns from bright green to deep orange with the temperature controlled from 85 K to 240 K in a cryogenic environment. The maximum absolute sensitivity and relative sensitivity of this temperature-sensing material based on non-thermally coupled levels of Ho³⁺ ions reached 0.049 K^-1 and 4.6% K^-1. And utilizing the thermochromic luminescence properties and high sensitivity for low temperature of the KLa(MoO₄)₂:Yb³⁺/Ho³⁺ UC material, we created KLa(MoO₄)₂:Yb³⁺/Ho³⁺ fluorescent security inks and UC photonic barcodes to realize novel visual reading and digital recognition dual-mode anti-counterfeiting in a secure manner. These results may provide useful enlightenment for the design and modulation of high-sensitivity temperature-sensing materials for high-level anti-counterfeiting applications.