Ultra-Large Unilamellar Nanosheets Efficiently Exfoliated From Y/Gd/Dy Layered Rare-Earth Hydroxides And Their Self-Assembly Into Highly Fluorescent Films

In this dissertation,ultra-large of layered rare-earth hydroxides for?LRHs?,with a series of ultra-large layered rare-earth hydroxides?LRHs?of(Y_0.975-xGd_xDy_0.025)₂?OH?₅N_O3·nH₂O have been successfully synthesized,oxide phosphors of excellent photoluminescence through proper annealing.Moreover,the hydrothermal ion exchange between the interlayer nitrate and the oleate anion,highly exfoliation of nanosheets and their self-assembly into highly fluorescent films have been syetematiclly studied.Detailed characterizations of the products were performed by the combined techniques of XRD,FT-IR,TG/DTA,FE-SEM,TEM,SAED,AFM and PLE/PL analysis.Ternary LRHs solid solutions of(Y_0.975-xGd_xDy_0.025)₂?OH?₅NO₃·nH₂O?x=0-0.975?have been successfully synthesized via hydrothermal reaction of the rare-earth nitrate/NH₄OH system in the presence of ammonium nitrate?NH₄NO₃?at 180 ? for 24 h.The results indicated that hexagonal shaped LRHs crystals are well crystallized with smooth surfaces.Smaller and thinner LRHs particles,and expanded lattice parameters a and b were found at a higher Gd³⁺ content,while the interlayer distance?c/2?,closely related to the hydration number n,is inversely proportional to the Gd³⁺ content.At the optimal Gd³⁺content of 2.5.at%,the fluorescence emission intensity are strongest.Increasing Gd³⁺ content leads the emission color of(Y_0.975-xGd_xDy_0.025)₂?OH?₅NO₃·nH₂O shifting from green to yellow.Calcining LRHs at 800 ? directly yields cubic(Y_0.975-xGd_xDy_0.025)₂O₃ phosphors,which inherited the morphologies of their precursors.Upon UV excitation at 270 nm(the ⁸S_7/2?⁶I_J transition of Gd³⁺),the oxide phosphors exhibit the characteristic yellow emission of Dy³⁺ at 576 nm(the ⁴F_9/2?⁶H_13/2 transition),suggesting the occurrence of energy transfer from Gd³⁺ to the activator,and enhanced luminescence was found for a higher Gd³⁺content.The nitrate ions,existing in the interlayer gallery of Y/Gd/Dy complex layered rare earth hydroxide,exhibit facile exchanges with oleate anions.Furthermore,the interlayer distance can thus be expanded from?0.89 nm for the pristine LRHs to?3.14 nm for the intercalated ones.A transparent colloidal solution with clear Tynall effects was obtained by dispersing the exchanged compound of(Y_0.95Gd_0.025DY_0.025)₂?OH?₅(C₁₇H₃₃COO)(C₁₇H₃₃COOH)_m·nH₂O in toluene under magnetic stirring for 24 h.Nanosheet films with a high[001]orientationwas self-assembled on a quartz substrate by a spin-coating process.Oxide films with a high[111]orientation will be constructed through calcining the LRHs films under proper annealing?800 ?,2 h?.The strongest fluorescence emissions were found for the x=0.3 sample,and the CIE chromaticity coordinate and fluorescence lifetimes are independent on the Gd³⁺ content.