Tens of micron-sized unilamellar nanosheets of Y/Eu layered rare-earth hydroxide: efficient exfoliation via fast anion exchange and their self-assembly into oriented oxide film with enhanced photoluminescence.

Layered rare-earth hydroxide (LRH) crystals of (YEu)(OH)NO·HO with a lateral size of ∼ 300 m and a thickness of ∼ 9 m have been synthesized via a hydrothermal reaction of mixed nitrate solutions in the presence of mineralizer NHNO at 200 °C for 24 h. LRH exhibits the ability to undergo intercalation and anion exchange with DS (CHOSO) via hydrothermal treatment. Compared with traditional anion exchange at room temperature, hydrothermal processing not only shortens the anion exchange time from 720 to 24 h but also increases the basal spacing. The arrangements of DS in the interlayer of LRH are significantly affected by the DS concentration and reaction temperature, and the basal spacing of the LRH-DS sample in the crystal edge is assumed to be larger than that in the crystal center. A higher DS concentration and reaction temperature both induce more intercalation of DS anions into the interlayer gallery, thus yielding a larger basal spacing. Unilamellar nanosheets with a lateral size of ≽60 m and a thickness of ∼ 1.6 nm can be obtained by delaminating LRH-DS in formamide. The resultant unilamellar nanosheets are single crystalline. Transparent (YEu)O phosphor films with a uniform [111] orientation and a layer thickness of ∼ 90 nm were constructed with the nanosheets as building blocks via spin-coating, followed by proper annealing. The oriented oxide film exhibits a strong red emission at 614 nm (the D-F transition of Eu), whose intensity is ∼ 2 times that of the powder form owing to the significant exposure of the (222) facets.