The phosphors Ba2Mg(BO3)2 activated with Ce3+ and Eu2+ ions are prepared by a solid-state reaction method at high-temperature and the Rietveld structure refinement of the host compound is performed. The synchrotron radiation VUV - UV excitation, UV – vis emission and luminescence decay spectra, as well as the dependencies of luminescence intensity and lifetime on doping content and temperature are systematically investigated. In addition, the electron-vibrational interaction (EVI) of Eu2+ ions with coordination surroundings and the Ce3+→Eu2+ energy transfer (ET) dynamics are studied in detail. Based on above discussion, the potential applications of co-doped phosphors in excitation wavelength and temperature dual-response optical anti-counterfeiting are demonstrated.

Ce3+-doped LiSr4(BO3)3phosphors have been prepared by a high-temperature solid-state reaction method, andstructural refinement of the host compound has been performed.The excitation and emission spectra in the vacuum ultraviolet-ultraviolet-visible range at cryogenic temperatures reveal that Ce3+ions preferentially occupy eight-coordinated Sr2+sites inLiSr4(BO3)3. Such experimental attribution is well corroboratedby the calculated 4f-5d transition energies and defect formationenergies of Ce3+ions at two distinct Sr2+sites in thefirst-principlesframework. In addition, the doping concentration-dependentluminescence and the temperature-dependent luminescence aresystematically investigated by luminescence intensity and lifetimemeasurements, respectively. This shows that concentration quenching does not occur in the investigated doping range, butinhomogeneous broadening exists in the concentrated samples. With the estimated thermal quenching activation energy, thediscussions on the thermal quenching mechanisms suggest that the thermal-ionization process of the 5d electron is a dominantchannel for thermal quenching of Ce3+luminescence, despite the fact that thermally activated concentration quenching cannot beexcluded for the highly doped samples. Finally, the X-ray excited luminescence measurement demonstrates the promisingapplications of the phosphors in X-ray detection

Palette for security. The “concentration palette” strategy enables the design of lanthanide-activated phosphors with temperature-responsive colour and orange intensity co-evolution, which are also used to fabricate superior security tag prototypes.

Ce3+ and Eu2+ doped and Ce3+-Eu2+ co-doped Sr2MgSi2O7 phosphors are prepared via a high-temperature solid-state reaction technique. The synchrotron radiation vacuum ultraviolet-ultraviolet (VUV-UV) excitation and ultraviolet-visible (UV-vis) emission spectra of diluted Ce3+ and Eu2+ doped Sr2MgSi2O7 samples are measured at cryogenic temperatures. The electron-vibrational interaction (EVI) between Ce3+ and its surroundings is analyzed. The dependencies of the 4f-5d transitions of Ce3+ on the structure of the host compounds Sr2MgSi2O7, Ba2MgSi2O7 and BaMg2Si2O7 are discussed in detail. Then the thermal quenching channel is proposed based on the measurements of temperature dependent luminescence intensities and decay times of Ce3+ and Eu2+ in Sr2MgSi2O7, and the Ce3+ → Eu2+ energy transfer mechanism is understood by three luminescence dynamic models. In addition, Sr2MgSi2O7:Ce3+/Eu2+ samples are evaluated for the possibilities of X-ray detection applications using X-ray excited luminescence (XEL) spectroscopy, and it was found that they are not suitable.

Due to the change of band gap, the photoluminescence and persistent luminescence performances of Ce3+ in Sr2(Ga,Al)2SiO7 have been optimized by the regulation of Al3+/Ga3+.

Eu2+-, Mn2+- and Eu2+-Mn2+-doped CaMgSi2O6 phosphors have been prepared by a high-temperature solid-state reaction. Systematic investigation of the concentration- and temperature-dependent luminescence of Mn2+ showed that Mn2+ ions occupy two distinct sites in CaMgSi2O6. Electron-vibration interaction (EVI) analyses of Mn2+ ions revealed Huang-Rhys factors of 4.73 and 2.82 as well as effective phonon energies of 313 and 383 cm(-1) for the two sites. Eu2+-Mn2+ energy transfer is also discussed, and its efficiency is estimated by lifetime and luminescence spectra. The different thermal quenching behaviours of Eu2+ and Mn2+, the distinct emission colours of Eu2+ (blue, band peak at similar to 451 nm) and Mn2+ (yellow-red range, band peaks at similar to 583 and 693 nm) endow the co-doped samples with potential applications in luminescence thermometry and temperature-/excitation wavelength-responsive dual anti-counterfeiting.

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+, Eu2+/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 CaMgSi2O6 are 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.

Ce3+ and Eu2+ single- and double-doped CaMgSi2O6 phosphors have been prepared by a high-temperature solid-state reaction approach. The VUV–UV–vis luminescence properties are investigated at cryogen...

Ce³⁺ and Eu²⁺ single- and double-doped CaMgSi₂O₆ phosphors have been prepared by a high-temperature solid-state reaction approach. The VUV–UV–vis luminescence properties are investigated at cryogenic temperatures. The dependencies of luminescence intensity and lifetime on temperature are discussed in detail, and the different thermal-quenching characteristics of luminescence of Ce³⁺ and Eu²⁺ in CaMgSi₂O₆ are revealed combined with the VRBE scheme. Because of the different energy barriers of the lowest 5d energy and the conduction band bottom, luminescence thermal quenching of Ce³⁺ does not occur below about 505 K, but that of Eu²⁺ arises at a temperature above ∼300 K. The energy transfer dynamics is then analyzed by using the Inokuti-Hirayama, Yokota-Tanimoto, and Burshtein models, respectively. The Ce³⁺–Eu²⁺ energy transfer is mainly through the electric dipole–dipole interaction with a critical distance of about 21.2 A, and the energy migration between Ce³⁺ ions in a fast or slow way is negligible. The different thermal-quenching behaviors of Ce³⁺ and Eu²⁺ luminescence and their energy transfer pave the way for the potential applications of the codoped samples in optical thermometry and anticounterfeiting.