Synthesis of Eu2+/Eu3+ Co-Doped Gallium oxide nanocrystals as a full colour converter for white light emitting diodes

Mechanistic study of Eu single atoms occupying four vacancy centers as potential electrocatalysts for the oxygen reduction reaction

The oxygen reduction reaction (ORR) on the oxygen electrode plays a critical role in rechargeable metal-air batteries, and the development of electrochemical energy storage and conversion technologies for the ORR is of great significance. In this study, the catalytic performance of rare earth-doped graphene (EuNxC6-x-Gra) as an electrocatalyst for the ORR was investigated. The results showed that a majority of the catalysts exhibited good ORR catalytic activity under acidic conditions, with some approaching or even surpassing commercial Pt-based catalysts (ηORR = 0.45 V). Particularly, EuN2C4-2-Gra demonstrated an ηORR of 0.38 V. It has been observed that the f-band center of Eu atoms increases with an increasing number of N atoms, and the charge distribution exhibits a "U" shape. There is a decreasing trend from N0 to N3 and an increasing trend from N4 to N6. By incorporating the proportional relationship of the adsorption free energies of reaction intermediates (ΔG*ads), a volcano diagram was constructed to rapidly assess catalytic activity. Finally, an intrinsic characteristic descriptor φ was formulated to quantitatively describe the relationship between φ and ηORR, providing a new tool for predicting and designing catalysts. This will provide guidance for the development and design of high-performance rare earth single atom catalysts.

Dual-mode optical thermometry design in K3YSi2O7:Eu multi-site phosphor

In this study, a dual-mode optical thermometer is designed based on radiative transitions from Eu³⁺ and Eu²⁺ ions at different K₃YSi₂O₇ lattice sites. In the luminescence-intensity-ratio strategy, a ratiometric signal composed of Eu³⁺:⁵D₀→⁷F₁ and Eu³⁺:⁵D₀→⁷F₂ emissions at 593 and 616 nm, respectively, is employed. Meanwhile, the intensity ratio of the 593-nm emission under O^2-→Eu³⁺ charge transfer excitation (λ_ex= 249 nm) to that upon Eu²⁺:4f⁷→4f⁶5d¹ excitation (λ_ex= 349 nm) is selected as a thermometric parameter in the single-band-ratio approach. The study findings show that combining the two strategies is conducive to the improvements in sensing-sensitive and anti-interference performance.

Regulation of Local Site Structures to Stabilize Mixed-Valence Eu2+/3+ under a Reducing Atmosphere for Multicolor Photoluminescence

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 Eu-doped Sr_1.95+xLi_1-xSi_1-xAl_xO₄F (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 Si⁴⁺-Li⁺ ion pairs with Al³⁺-Sr²⁺ ion pairs compresses the Sr sites occupied by Eu²⁺, and it stabilizes Eu³⁺ in a reducing atmosphere and leads to the coexistence of Eu²⁺ and Eu³⁺ in single-phase Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu (0 ≤ x ≤ 0.25) phosphors. Based on the wavelength-dependent luminescence color behaviors of Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu phosphors, the fluorescent anticounterfeit papers/patterns containing Sr_1.95+xLi_1-xSi_1-xAl_xO₄F: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 Eu²⁺ (530 nm) and Eu³⁺ (703 nm), Sr_1.95+xLi_1-xSi_1-xAl_xO₄F: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+xLi_1-xSi_1-xAl_xO₄F: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+xLi_1-xSi_1-xAl_xO₄F to the fields of multicolor anticounterfeiting and noncontact optical thermometry.

Control of Eu Oxidation State in Y2O3-xSx:Eu Thin-Film Phosphors Prepared by Atomic Layer Deposition: A Structural and Photoluminescence Study

Structural and photoluminescence studies were carried out on Eu-doped Y₂O_3−xS_x thin films grown by atomic layer deposition at 300 °C. (CH₃Cp)₃Y, H₂O, and H₂S were used as yttrium, oxygen, and sulfur precursors, respectively, while Eu(thd)₃ was used as the europium precursor. The Eu oxidation state was controlled during the growth process by following the Eu(thd)₃ pulse with either a H₂S or O₃ pulse. The Eu(thd)₃/O₃ pulse sequence led to photoluminescence emission above 550 nm, whereas the Eu(thd)₃/H₂S pulse sequence resulted in emission below 500 nm.