Structure, luminescence of Eu²⁺and Eu³⁺in CaMgSi₂O₆and their co-existence for the excitation-wavelength/temperature driven colour evolution

Abstract

Luminescent materials with controllable colour evolution features are demanded for the development of multi-level anti-counterfeiting technologies. Here we report the structural and luminescence properties of CaMgSi₂O₆:Ln (Ln = Eu²⁺, Eu³⁺, Eu^2+/3+) samples in detail and reveal their excitation-wavelength/temperature driven colour evolution characteristics. By tuning either the excitation-wavelength (276, 304, 343, 394 nm) or temperature (in the 330-505 K range), the designed samples with co-existing Eu²⁺/Eu³⁺ions can achieve diverse and controllable colour evolution from red, to pink, purple and blue. This shows their potential application in anti-counterfeiting with the help of sophisticated pattern design. In addition, the underlying mechanism of the Stokes shift of the Eu²⁺emission and valence stability of both Eu²⁺/Eu³⁺ions in CaMgSi₂O₆are also studied in depth. These results are valuable for designing colour-controllable luminescent materials based on the co-existence of the Eu²⁺/Eu³⁺ions for anti-counterfeiting applications.