Influence of Na+ ion doping on the phase change and upconversion emissions of the GdF3: Yb3+, Tm3+ nanocrystals obtained from the designed molecular precursors

Abstract

Bottom-up synthesis of a series of GdF₃ nanocrystals (NCs) co-doped with 20 mol% Yb³⁺, 2 mol% Tm³⁺ and varying amount of Na⁺ ions is reported using novel molecular precursors [Ln₂(TFA)₆(diglyme)₂] [Ln = Gd (1), Tm (2), Yb (3)] and [Na₄(TFA)₄(diglyme)]_∞ (4) [TFA = CF₃COO⁻; diglyme = MeO(CH₂CH₂O)₂Me]. The single crystal X-ray structures of the new complexes 1–4, which act as excellent precursors because of the absence of water molecules and the ability of the diglyme ligand to behave as a capping reagent during decomposition to render the nanoparticles monodisperse in organic solvents, show a versatile bonding mode of the TFA (dangling η¹ or bridging μ,η¹,η¹; μ₄-η¹:η¹:η¹:η¹- and μ₄-η¹:η¹:η¹:η² (O, F)) and diglyme (η³ or μ-η³:η¹) ligands. The influence of Na⁺ ion doping on the phase change and upconversion emissions of these GdF₃: Yb³⁺, Tm³⁺ NCs was studied and compared with the upconversion (UC) intensity of the well-known upconverting NaGdF₄: Yb³⁺, Tm³⁺ NCs. Among the several UC samples studied, the GdF₃: Yb³⁺, Tm³⁺ NCs with 30 mol% Na⁺ seemed to be the most promising as a red emitting UC phosphor, emitting more photons than the NaGdF₄: Yb³⁺, Tm³⁺ UC NCs in the near IR region.