Inverse thermal quenching effect in lanthanide-doped upconversion nanocrystals for anti-counterfeiting†
It is common that thermal quenching in luminescent materials inevitably occurs with an elevation in temperature. Herein, an inverse thermal quenching effect in lanthanide-doped upconversion nanocrystals was reported. Specifically, defects with an appropriate energy state were designed in Yb/Er (Ho, Tm) doped Na3ZrF7 nanocrystals to actualize a thermal-induced enhancement in luminescent intensity. Owing to this special temperature dependent optical property, our results reveal that these kinds of materials are very suitable for high security anti-counterfeiting applications.