The effects of Gd3+ substitution on the crystal structure, site symmetry, and photoluminescence of Y/Eu layered rare-earth hydroxide (LRH) nanoplates

Well crystallized nanoplates of the (Y0.95-xGdxEu0.05)(2)(OH)(5)NO3 center dot nH(2)O ternary layered rare-earth hydroxides (LRHs), synthesized hydrothermally, have been investigated with emphasis on the effects of Gd3+ substitution for Y3+ on the structural features and optical properties. Characterizations of the materials were achieved by the combined techniques of XRD, FT-IR, TEM, DTA/TG, and optical spectroscopies. The results showed that Gd3+ substitution leads to linearly expanded ab plane, shortened interlayer distance (c/2), and reduced hydration (smaller n value) of the crystal structure. As a consequence, the Ln(3+) partially shifts from the C-4v to C-1 site symmetries and thus leads to systematically altered photoluminescence behaviors. Under the F-7(0)-->L-5(6) transition excitation of Eu3+ at 394 nm, both the D-5(0)-->F-7(2) to D-5(0)-->F-7(4) and the 595 nm D-5(0)-->F-7(1) to 590 nm D-5(0)-->F-7(1) intensity ratios linearly increase towards a higher Gd3+ content. The incorporated Gd3+ cations selectively sensitize emission from the C-1-site Eu3+ and produce a new charge transfer (CT) excitation band at similar to 254 nm. With this, the desired 615-nm red emission is obtainable either under intra-4f(6) transition excitation of Eu3+ or by exciting the CT band. The materials have similar fluorescence lifetimes of 0.85 +/- 0.05 ms for the 615-nm emission, irrespective of the Gd3+ content and excitation wavelength.