Site preferences of dopant Eu on the locations of K, Ba, and Ca in the mixed cation phosphate KBaCa(PO) (KBCP) are quantitatively analyzed via a combined experimental and theoretical method to develop a blue-emitting phosphor with thermally stable luminescence. Eu ions are located at K2 (M2) and K3 (M3) sites of KBCP, with the latter occupation relatively more stable than the former, corresponding to emissions at 438 and 465 nm, respectively. KBCP:Eu phosphor exhibits highly thermal stable luminescence even up to 200 °C, which is interpreted as due to a balance between thermal ionization and recombination of Eu 5d excited-state centers with the involvement of electrons trapped at crystal defect levels. Our results can initiate more exploration of activator site engineering in phosphors and therefore allow predictive control of photoluminescence tuning and thermally stable luminescence for emerging applications in white LEDs.

Composite nanomaterials are attractive for a diverse range of applications in catalysis, plasmonics, sensing, imaging, and biology. In such composite nanomaterials, it is desired, yet still challenging to create a controlled alignment between components with lattices in disparate scales. To address this challenge, we report a new concept of colloidal synthesis, in which self-assembled molecular layers control the alignment between materials during the synthesis. To illustrate this concept, self-assembled cetyltrimethylammonium bromide (CTAB) molecules are used to control interfaces in a core-shell nanocomposite with a well-defined metal nanocrystal core and a metal-organic-framework (MOF) shell, which differ in structural dimensions by orders of magnitude. We show that single metal nanocrystals are captured individually in single-crystalline MOFs, and an alignment between the {100} planes of the metal and {110} planes of the MOFs is observed. By utilizing the same concept, a layer of mesostructured silica is formed over MOF crystals. These multilayered core-shell structures demonstrate a controlled alignment across a wide range of materials, from the metal nanocrystals, extending to nanoporous MOFs and mesostructured silica.

Near-infrared (NIR) light-emitting diodes (LEDs) light sources are desirable in photonic, optoelectronic, and biological applications. However, developing broadband red and NIR-emitting phosphors with good thermal stability is always a challenge. Herein, the synthesis of Eu 2+ -activated SrY 2 O 4 red phosphor with high photoluminescence quantum efficiency and broad emission band ranging from 540 to 770 nm and peaking at 620 nm under 450 nm excitation is designed. Sr/Ba substitution in SrY 2 O 4 :Eu 2+ has been further utilized to achieve tunable emission by modifying the local environment, which facilitates the giant redshifted emission from 620 to 773 nm while maintaining the outstanding thermal stability of SrY 2 O 4 :Eu 2+ . The NIR emission is attributed to the enhanced Stokes shift and crystal field strength originated from the local structural distortions of [Y1/Eu1O 6 ] and [Y2/Eu2O 6 ]. The investigation in charge distribution around Y/Eu provides additional insight into increasing covalency to tune the emission toward the NIR region. As-fabricated NIR phosphor-converted LEDs demonstration shows its potential in night-vision technologies. This study reveals the NIR luminescence mechanism of Eu 2+ in oxide-based hosts and provides a design principle for exploiting Eu 2+ -doped NIR phosphors with good thermal stability.

The hydroxide‐exchange membrane fuel cell (HEMFC) is a promising energy conversion device. However, the development of HEMFC is hampered by the lack of platinum‐group‐metal‐free (PGM‐free) electrocatalysts for the hydrogen oxidation reaction (HOR). Now, a Ni catalyst is reported that exhibits the highest mass activity in HOR for a PGM‐free catalyst as well as excellent activity in the hydrogen evolution reaction (HER). This catalyst, Ni‐H2‐2 %, was optimized through pyrolysis of a Ni‐containing metal‐organic framework precursor under a mixed N2/H2 atmosphere, which yielded carbon‐supported Ni nanoparticles with different levels of strains. The Ni‐H2‐2 % catalyst has an optimal level of strain, which leads to an optimal hydrogen binding energy and a high number of active sites.

Structure-property relations of Ag2-3xBixI2 have been revealed.