Sacrificial conversion of layered rare-earth hydroxide (LRH) nanosheets into (Y1−xEux)PO4 nanophosphors and investigation of photoluminescence

Abstract

Ultra-thin nanosheets (2–6 nm) of the (Y_1−xEu_x)₂(OH)₅NO₃·nH₂O layered rare-earth hydroxide (LRH), directly crystallized without exfoliation were employed for the first time as a sacrificial precursor to synthesize (Y_1−xEu_x)PO₄ orthophosphate red phosphors via nano-conversion, and anion exchange of both the hydroxyls and NO₃⁻ in the LRH with the phosphate ions from diammonium hydrogen phosphate ((NH₄)₂HPO₄) is discussed. Detailed characterization of the materials was performed by the combined techniques of XRD, FTIR, TG/DSC, FE-SEM, HR-TEM, and photoluminescence spectroscopy. The (Y_1−xEu_x)PO₄ phosphors, with crystallite sizes of up to ∼20 nm, were found to exhibit stronger ⁵D₀ → ⁷F₂ (621 nm) than ⁵D₀ → ⁷F₁ (595 nm) emissions under charge transfer excitation (236 nm) owing to the nano-size effect. The optimal Eu³⁺ content was determined to be ∼10 at% (x = 0.10), and concentration quenching of luminescence was analyzed to result from exchange interactions. The effects of the Eu³⁺ content and annealing temperature on the structural features and luminescence properties of the (Y_1−xEu_x)PO₄ nanophosphors were discussed in detail, including emission intensity, the asymmetry factor of luminescence, fluorescence lifetime, and CIE chromaticity coordinates.