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 (Y(0.95)Eu(0.05))(2)(OH)(5)NO(3)·nH(2)O with a lateral size of ∼ 300 μm and a thickness of ∼ 9 μm have been synthesized via a hydrothermal reaction of mixed nitrate solutions in the presence of mineralizer NH(4)NO(3) at 200 °C for 24 h. LRH exhibits the ability to undergo intercalation and anion exchange with DS(−) (C(12)H(25)OSO(3)(−)) 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 μm and a thickness of ∼ 1.6 nm can be obtained by delaminating LRH-DS in formamide. The resultant unilamellar nanosheets are single crystalline. Transparent (Y(0.95)Eu(0.05))(2)O(3) 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 (5)D(0)–(7)F(2) transition of Eu(3+)), whose intensity is ∼ 2 times that of the powder form owing to the significant exposure of the (222) facets.