Novel heterometal-organic complexes as first single source precursors for up-converting NaY(Ln)F₄(Ln = Yb, Er, Tm) nanomaterials

Abstract

First heterometal-organic single source precursors for NaYF(4) nanomaterials as a host matrix for up-conversion emission are reported. These novel heterobimetallic derivatives NaY(TFA)(4)(diglyme) (1), [Na(triglyme)(2)][Y(2)(TFA)(7)(THF)(2)] (2) and Na(2)Y(TFA)(5)(tetraglyme) (3) (TFA = trifluoroacetate), which were fully characterized by elemental analysis, FT-IR and (1)H NMR spectroscopy, TG-DTA data as well as single crystal X-ray structures, are advantageous in terms of being anhydrous and having lower decomposition temperatures in comparison to the homometallic precursor Y(TFA)(3)(H(2)O)(3). In addition, they also contain chelating glyme ligands, which act as capping reagents during decomposition to control the NaYF(4) particle size and render them monodisperse in organic solvents. On decomposition in 1-octadecene, the molecular derivatives 1 and 3 are converted, in the absence of any surfactant or capping reagent, to cubic NaYF(4) nanocrystals at significantly lower temperatures (below 250 °C). At higher temperature, a mixture of the cubic and hexagonal phases was obtained, the relative ratio of the two phases depending on the reaction temperature. A pure hexagonal phase, which is many folds more efficient for UC emission than the cubic phase, was obtained by calcining nanocrystals of mixed phase at 400 °C. In order to co-dope this host matrix with up-converting lanthanide cations, analogous complexes NaLn(TFA)(4)(diglyme) [Ln = Er (4), Tm (5), Yb (6)] and Na(2)Ln(TFA)(5)(tetraglyme) [Ln = Er (7), Yb (8)] were also prepared and characterized. The decomposition in 1-octadecene of suitable combinations and appropriate molar ratios of these yttrium, ytterbium and erbium/thulium derivatives gave cubic and/or hexagonal NaYF(4): Yb(3+), Er(3+)/Tm(3+) nanocrystals (NCs) capped by diglyme or tetraglyme ligands, which were characterized by IR, TG-DTA data, EDX analysis and TEM studies. Surface modification of these NCs by ligand exchange reactions with poly acrylic acid (PAA) and polyethyleneglycol (PEG) diacid 600 was also carried out to render them water soluble. The THF solutions of suitable combinations of the diglyme derivatives were also used to elaborate the thin films of NaYF(4):Yb(3+), Er(3+)/Tm(3+) on a glass or Si wafer substrate by spin coating. The multicolour up-conversion fluorescence was successfully realized in the Yb(3+)/Er(3+) (green/red) and Yb(3+)/Tm(3+) (blue/violet) co-doped NaYF(4) nanoparticles and thin films, which demonstrates that they are promising UC nanophosphors of immense practical interest. The up-conversion excitation pathways for the Er(3+)/Yb(3+) and Tm(3+)/Yb(3+) co-doped materials are discussed.

Analysing the effect of the crystal structure on upconversion luminescence in Yb3+,Er3+-co-doped NaYF4 nanomaterials

“…For annealing temperatures in the range of 300 1C o T an o 600 1C a distinct increase in the overall upconversion luminescence intensity was found with a maximum at T an = 500 1C. 18,[68][69][70] In addition, for this set of samples the spectral intensity distribution was changed as well. Within different emission bands (G1, G2, and R) Stark level-related substructures became apparent, but also the relative contribution of the G-and R-bands was altered (see Fig.…”

Glymes as versatile solvents for chemical reactions and processes: from the laboratory to industry

“…Shirahata and Sakka 346 synthesized highly luminescent Si nanoparticles (NPs) terminated with alkoxy monolayers through the reduction SiCl 4 by sodium biphenylide in a toluene + monoglyme mixture using an inverse micelle method; they also observed the size-dependent UV photoluminescence (PL) property for non-oxidized Si NPs at room temperature, as well as a high quantum efficiency of the UV fluorescence. Mishra et al 347 prepared heterometal-organic complexes including NaY(TFA) 4 (diglyme), [Na(triglyme) 2 ][Y 2 (TFA) 7 (THF) 2 ], Na 2 Y(TFA) 5 (tetraglyme), NaLn(TFA) 4 (diglyme) [Ln = Er, Tm, or Yb], and Na 2 Ln(TFA) 5 (tetraglyme) [Ln = Er, or Yb] (TFA = trifluoroacetate), and used them as precursors for up-converting NaY(Ln)F 4 (Ln = Yb, Er, Tm) nanocrystals and thin films, which have potential applications as lanthanide-doped up-conversion (UC) emission materials.…”

Building Fluorinated Hybrid Crystals: Understanding the Role of Noncovalent Interactions

“…Metal-fluorine contacts present in these crystals provide a low-temperature pathway for their decomposition into the corresponding mixed-metal fluorides or oxifluorides, thereby making fluorinated hybrid crystals ideal single-source precursors for solution-phase routes to compositionally complex functional materials. 4,[11][12][13][14] One of the main challenges facing the design and predictive synthesis of fluorinated hybrid crystals is the lack of quantitative understanding of the role of metal-fluorine noncovalent interactions in determining their crystal-chemistry. Of particular importance is the understanding of the electronic and steric effects of these interactions on metal connectivity and coordination, which ultimately dictate crystal cohesion.…”