Sulfate Exchange of the Nitrate-Type Layered Hydroxide Nanosheets of Ln2(OH)5NO3•nH2O for Better Dispersed and Multi-color Luminescent Ln2O3 Nanophosphors (Ln = Y0.98RE0.02, RE = Pr, Sm, Eu, Tb, Dy, Ho, Er, and Tm)

Through restricting thickness growth by performing coprecipitation at the freezing temperature of similar to 4 degrees C, solid-solution nanosheets (up to 5-nm thick) of the Ln(2)(OH)(5)NO3 center dot nH(2)O layered hydroxide (Ln = Y0.98RE0.02; RE = Pr, Sm, Eu, Tb, Dy, Ho, Er, and Tm, respectively) were directly synthesized without performing conventional exfoliation. In situ exchange of the interlayer NO3- with SO42- produced a sulfate derivative [Ln(2)(OH)(5)(SO4)(0.5)center dot nH(2)O] of the same layered structure and two-dimensional crystallite morphology but substantially contracted d(002) basal spacing ( from similar to 0. 886 to 0.841 nm). The sulfate derivative was systematically compared against its nitrate parent in terms of crystal structure and phase/morphology evolution upon heating. It is shown that the interlayer SO42-, owing to its bonding with the hydroxide main layer, significantly raises the decomposition temperature from similar to 600 to 1000 degrees C to yield remarkably better dispersed oxide nanopowders via a monoclinic Ln(2)O(2)SO(4) intermediate. The resultant (Y0.98RE0.02)(2)O-3 nanophosphors were studied for their photoluminescence to show that the emission color, depending on RE3+, spans a wide range in the Commission Internationale de l'Eclairage (CIE) chromaticity diagram, from blue to deep red via green, yellow, orange, and orange red.