Regulation of Local Site Structures to Stabilize Mixed-Valence Eu^2+/3+ under a Reducing Atmosphere for Multicolor Photoluminescence

Abstract

Co-doping mixed-valence Eu 2+/3+ in a single-phase phosphor is an efficient method to realize the emission color regulation, which holds great potential for anticounterfeiting and ratiometric temperature sensing. Here, the mixed-valence Eudoped Sr 1.95+x Li 1−x Si 1−x Al x O 4 F (0 ≤ x ≤ 0.25) phosphors were designed and prepared under a reducing atmosphere. The correlation of local phase structures and luminescence properties was discussed. Replacing Si 4+ −Li + ion pairs with Al 3+ −Sr 2+ ion pairs compresses the Sr sites occupied by Eu 2+ , and it stabilizes Eu 3+ in a reducing atmosphere a n d le a d s t o t h e co e x i st e n c e of E u 2 + an d E u 3 + i n s i n g l e -p h a s e Sr 1.95+x Li 1−x Si 1−x Al x O 4 F:0.05Eu (0 ≤ x ≤ 0.25) phosphors. Based on the wavelengthdependent luminescence color behaviors of Sr 1.95+x Li 1−x Si 1−x Al x O 4 F:0.05Eu phosphors, the fluorescent anticounterfeit papers/patterns containing Sr 1.95+x Li 1−x Si 1−x Al x O 4 F:0.05Eu phosphors were the same as ordinary paper under ambient conditions. However, the hidden colors or images can be read out with green-orange luminescence under 365/300 nm light excitation. Benefiting from the diverse thermal response emission behaviors of Eu 2+ (530 nm) and Eu 3+ (703 nm), Sr 1.95+x Li 1−x Si 1−x Al x O 4 F:0.05Eu phosphors exhibit temperature sensing performances, with the maximum absolute and relative sensitivity being 0.0294 K −1 at 573 K and 0.83% K −1 at 348 K. More importantly, Sr 1.95+x Li 1−x Si 1−x Al x O 4 F:0.05Eu phosphors showed excellent stability in humid, acid, and alkali environments, which contributed to applying mixed-valence Eu 2+/3+ -doped Sr 1.95+x Li 1−x Si 1−x Al x O 4 F to the fields of multicolor anticounterfeiting and noncontact optical thermometry.

Precisely Manipulating the Self‐Reduction of Manganese in MgGa2O4 through Lithium Incorporation for Optical Thermometry and Anti‐Counterfeiting

“…Clearly, the obtained S r values are completely different, implying that the thermometric properties of the developed optical thermometers can be regulated by changing the excitation wavelength. Furthermore, as shown in Figure 5g, compared with those of previously developed optical thermometers, [2,11,19,24,[32][33][34][35][36][37][38][39][40][41] the obtained S r values are relatively good, making the yL-MGO:Mn phosphors promising candidates for non-invasive and remote temperature monitoring via the FIR technique.…”

Luminescence Enhancement of Red‐Emitting Sr9MnK(PO4)7 Phosphor via Energy Transfer and Charge Compensation

“…Recently, mixed‐valence Eu‐activated phosphors have received great attention from researchers to realize multicolor luminescence. [ 22 ] Various Eu‐doped phosphors with mixed Eu 2+/3+ valence states were obtained. [ 23 ] The Eu ions in the SMKP host substitute Sr and create Sr vacancies () via .…”

Recent Advances in Multi-Site Luminescent Materials: Design, Identification and Regulation

“…The luminescence can be modified via the structural evolution of the multi-site compounds. Figure 7 a illustrates the structure model of Sr 2 LiSiO 4 F with two kinds of Sr sites [ 79 ]. Due to the substitution of the Sr 2+ -Al 3+ pair by the Li + -Si 4+ pair, the local structure of Sr sites where activator ions are doped is changed, as shown in Figure 7 b.…”