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.

In this work, the crystal structure and electronic structure as well as the synchrotron radiation vacuum ultraviolet-ultraviolet-visible (VUV-UV-vis) luminescence properties of Li ₆ Y(BO ₃ ) ₃ (LYBO):Ce ³⁺ phosphors were investigated in detail. The Rietveld refinement and DFT calculation reveal the P2 ₁ /c monoclinic crystal phase and the direct band gap of the LYBO compound, respectively. Only one kind of Ce ³⁺ 4f-5d transition is resolved in terms of the low temperature VUV-UV excitation, UV-vis emission spectra and luminescence decay curves. Furthermore, by constructing the vacuum referred binding energy (VRBE) scheme and applying the frequency-degenerate vibrational model, the impacts of 5d electron binding energy and electron-phonon coupling on luminescence of Ce ³⁺ in LYBO are analysed. The results show that the Ce ³⁺ emission in LYBO possesses a moderate intrinsic thermal stability. With the increase in concentration, the thermal stability of the emission gets worse due to the possible thermally-activated concentration quenching. In addition, the simulation of Ce ³⁺ emission profile at low temperature reveals that the 4f-5d electronic transitions of Ce ³⁺ ions can be treated to couple with one frequency-degenerate vibrational mode having the effective phonon energy of ∼257 cm ⁻¹ with the corresponding Huang-Rhys parameter of ∼6, which indicates a strong electron-phonon interaction of Ce ³⁺ luminescence in the Li ₆ Y(BO ₃ ) ₃ host. Finally, the X-ray excited luminescence spectrum of the LYBO:5%Ce ³⁺ phosphor is measured to check the potential scintillator applications.

The host structure and the synchrotron radiation VUV-UV luminescence properties of samples BaMg₂Si₂O₇ (BMSO):Ln (Ce³⁺, Eu²⁺) at different doping levels and different temperatures were investigated in detail. Three important aspects are studied to elucidate the luminescence properties of samples: (1) the vacuum referred binding energy (VRBE) scheme is constructed with the electron binding in the BMSO host bands and in the Ce³⁺ and Eu²⁺ impurity levels with the aim to explain the different thermal stabilities of Ce³⁺ and Eu²⁺ emissions; (2) the electron-vibrational interaction analysis on the narrow Eu²⁺ emission indicates a weak electron-phonon interaction in the current case; (3) by using three models (Inokuti-Hirayama, Yokota-Tanimoto, and Burshteǐn models) at different conditions, the energy transfer dynamics between Ce³⁺ and Eu²⁺ was analyzed. It reveals that the energy transfer from Ce³⁺ to Eu²⁺ via electric dipole-dipole (EDD) interaction is dominant while energy migration between Ce³⁺ is negligible. Finally, the X-ray excited luminescence spectra of samples BMSO:Ce³⁺/Eu²⁺ are collected to evaluate their possible scintillator applications.