Hydrothermal conversion of layered hydroxide nanosheets into (Y0.95Eu0.05)PO4 and (Y0.96−xTb0.04Eux)PO4 (x = 0–0.10) nanocrystals for red and color-tailorable emission

Abstract

Tetragonal-structured (Y_0.95Eu_0.05)PO₄ and (Y_0.96−xTb_0.04Eu_x)PO₄ nanocrystals were sacrificially converted from layered rare-earth hydroxide (Ln₂(OH)₅NO₃·nH₂O, LRH) nanosheets via hydrothermal reaction and in the presence of ammonium dihydrogen phosphate (NH₄H₂PO₄). Detailed characterizations of the materials were achieved by the combined techniques of FT-IR, ICP, XRD, FE-SEM, TEM, and optical spectroscopies, and the mechanisms of anion exchange and hydrothermal conversion were discussed. Phase structure and morphology of the product were found to heavily rely on the amount of PO₄³⁻ relative to rare-earth ions. The effects of calcination were studied in detail with the (Y_0.95Eu_0.05)PO₄ red phosphor nanocrystals. The (Y_0.96−xTb_0.04Eu_x)PO₄ ternary phosphors present efficient Tb³⁺ → Eu³⁺ energy transfer through electric dipole–dipole interactions, with which the emission color can be facilely tuned from green to red via yellow by raising the Eu content. The efficiency of energy transfer was analyzed to be ∼40.7% at the optimal Eu³⁺ concentration of 8 at% (x = 0.08).