Synthesis Of NaYF₄:Yb,Er With Highly Luminous Intensity And Their Properties Reseach

Rare-earth doped upconversion luminescent nanomaterials have a great deal of potential applications in many fields, due to their unique optical properties and outstanding physicochemical properties. However, their low luminescence efficiency is the main obstacle for their large-scale industrial applications. How to improve the emission efficiency of rare-earth doped upconversion luminescent nanomaterials is always the important pursue for the researchers. Especially, multifunctional upconversion luminescent nanomaterials have more demands with the development of their application in the fields of biology, biomedicine and solar cells. In this paper, both convenient and effective methods have been developed to improve the emission efficiency of NaYF4:Yb,Er upconversion luminescent nanomaterial. What’s more, small size, and water-soluble NaYF4:Yb,Er particles have also been obtained by simple synthetic methods。Hydro/solvent thermal method was used to synthesize NaYF4:Yb,Er nanocystal in this paper at the low reaction tempreture which has weak restriction on chelating ligand. When using oleic acid as the chelating ligand, luminous intensity of NaYF4:Yb,Er was enhanced obviously by tuning pH value of reaction solution with little NaOH or without NaOH. The enhancement factors of544nm emissions were48,42and32for samples prepared under pH5.9,6.9and7.4, respectively, compared with that of the product prepared under pH8.3.A series of new chelating ligands with different carbon chain length had selected for hydro/solvent thermal synthesis of NaYF4:Yb,Er nanocrystals, such as butanoic acid, hexanoic acid, decanoic acid, and tetradecanoic acid, for comparation, commonly used oleic acid was also used as ligand for hydrothermal synthesis of NaYF4:Yb,Er. The emission intensiy of NaYF4:Yb,Er increased dramatically with the decrease of carbon chain length of ligands. Take OA as comparison, the emission enhancement factors of544nm emission were25,21,6.5, and3for samples prepared with butanoic acid, hexanoic acid, decanoic acid, and tetradecanoic acid, respectively. NaYF4:Yb,Tm nanocrystals were prepared under the same reaction conditions, and the emission intensiy of NaYF4:Yb,Tm also increased dramatically with the decrease of carbon chain length of ligands.Different NaYF4:Yb,Er nanocystals were synthesized by changing the number of functional groups in chelating ligands. By increasing the number of carboxylic acid in ligands, such as hexanoic acid, hexanoic diacid, citric acid and ethylene diamine tetraacetic acid, the luminous intensity of NaYF4:Yb,Er became weaker; by increasing the number of amino-group in ligands as well, such as butyl amine, diethylene triamine, triethylene tetraamine and tetraethylene pentaamine, luminous intensity of NaYF4:Yb,Er also became weaker. All in all, with the increase of the number of functional groups in ligands, luminous intensity of NaYF4:Yb,Er became weaker.NaYF4:Yb,Er nanocystals with different sizes and luminous intensity were synthesized by changing the composition of solvent in reactions. When the ratio of water to ethanol (glycol) was1:3or smaller, NaYF4:Yb,Er nanocystals with small-scale size could be obtained. In addition, NaYF4:Yb,Er nanocystals with different water-solubilities could be synthesized by using different water-soluble ligands.