Promising excitation-responsive phosphors CaxMgSi2Ox+5: Eu2+, Dy3+ with dual-mode luminescent centers for advanced anti-counterfeiting technology

Abstract

Multi-mode luminescence typically produces tunable luminescent responses to different excitations. The formation of multi-mode luminescent centers in a single host is a promising research strategy that offers potential applications in the fields of multilayer advanced anti-counterfeiting technology and encryption technology. In this paper, we systematically studied the crystal structure, surface morphology, elemental composition, luminescence and afterglow properties of Ca_x-0.06MgSi₂O_x+5: Eu²⁺_0.01, Dy³⁺_0.05 (x = 1, 1.2, 1.6, 2) long afterglow phosphors. By continuously adjusting the composition of the Ca_xMgSi₂O_x+5 host, dual-mode luminescent centers were successfully constructed within a single silicate host in Ca_x-0.06MgSi₂O_x+5: Eu²⁺_0.01, Dy³⁺_0.05 (x = 1.2 or 1.6) samples. These dual-mode luminescence phosphors exhibit distinct patterns of changes in the excitation spectra, while still overlapping in certain energy regions, which belongs to the excitation-responsive photoluminescence characteristic. The dynamic variations in luminescence colors of the static materials from near-white to blue light (x = 1.2) and from near-white to light yellow-green light (x = 1.6) were achieved in by excitation wavelength modulation. Their potential applications in the field of multilayered advanced anti-counterfeiting technology were demonstrated by constructing complex patterns. The afterglow emissions of the samples with x = 1 and 1.2 demonstrate a color transformation property over time, which may facilitate further exploration of their applications in information encryption. Additionally, an in-depth study of the electronic structures of the hosts Ca₂MgSi₂O₇ and CaMgSi₂O₆, along with the doped luminescent center Eu and the co-doped activator Dy, has been systematically investigated using first-principles calculations, which elucidates the reasons for the differences in photoluminescence and afterglow properties between the two crystal phases Ca₂MgSi₂O₇: Eu²⁺, Dy³⁺ and CaMgSi₂O₆: Eu²⁺, Dy³⁺. These results are of great value and significance for the research on designing multi-mode luminescence centers with color-controllable properties in a single host.