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

Ultra-thin nanosheets (2–6 nm) of the (Y1−xEux)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 (Y1−xEux)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 (Y1−xEux)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 (Y1−xEux)PO4 nanophosphors were discussed in detail, including emission intensity, the asymmetry factor of luminescence, fluorescence lifetime, and CIE chromaticity coordinates.