Size Control,Growth Mechanism And Surface Modification Of NaYF₄ Upconversion Nanocrystals

Nobel laureate Feyneman predicted that if we controlled the arrangement of objects on small scale,the objects with many unusual features could be prepared and we can find the rich changes on the material performance.What the Feyneman said is nanomaterials.Since the 1980 s,nanomaterials have been the hot spot in the field of scientific research and had become a national strategy material.So far,nanomaterials have been applied in aircraft coating and space sensors,and in other civilian areas such as drug delivery,automobile manufacturing,nanomaterial is also developed.In the field of bioluminescence,lanthanide-doped fluorides nanomaterials have lower toxicity,narrow-band transmission and high light stability as compared to quantum dots and organic dyes.Nanomaterials with small size can easily enter into the tissues and free to move in the blood.Therefore,size control for NaYF₄ nanocrystals has important research significance.CdSe quantum dots?QDs?possessed of quantum confinement effect and long fluorescent lifetime have been widely concerned.We studied the size control,growth mechanism and surface modification of NaYF₄ upconversion nanocrystals.The main research contents of this paper are as follows:?1?In order to obtain the NaYF₄ nanocrystals with highly uniform size and shape,we developed and tested a device named Automatic nanomaterials synthesizer by combining many subjects,such as chemical,electrical and mechanical.Automatic nanomaterials synthesizer help the researchers to simplify the manual process of experimental operation,save the time and make the experimental result more stable and reliable.Under the program of “Use template”,automatic nanomaterials synthesizer can synthesize the NaYF₄ nanocrystals with 10 nm in diameter repeatedly by controlling the reaction temperature,reaction time,stirring speed,gas flow rate and feeding automatically.Under the program of “Advanced mode”,manipulators can set the parameters according to the experiment condition,which provides more convenient experimental conditions for operators.?2?The total amount of rare earth materials in a conventional preparation of NaYF₄:18%Yb³⁺,2%Er³⁺ nanocrystals is 2 mmol.In order to prepare the standard reaction liquid which can be used for a plurality of times with using the Automatic nanomaterials synthesizer and facilitate further experimental exploration,we prepared NaYF₄:18%Yb³⁺,2%Er³⁺ standard solution.In this way,the experimental errors caused by manual operation and experimental environment can be reduced to the greatest extent,and the results of synthesis and characterization are more convincing.?3?In order to obtain high quality NaYF₄ nanoparticles with different morphologies and sizes,we prepared the nanomaterials by using Automatic nanomaterials synthesizer.Meanwhile we explored the relationship between the crystal morphology and the high temperature reaction time in the preparation of NaYF₄:Yb³⁺,Er³⁺ by high temperature thermal decomposition.The results showed that the particle size of nanocrystals showed a uniform growth trend when the reaction time was set between 25 min and 45 min at 305 ?.However,when the reaction time was set to 45 min or more,due to the impact of Oswald ripening effect,the average particle size of the nanocrystals reduced.With the reaction time increased sequentially,the nanoparticles have a tendency to longitudinal grow into rods.In order to control the influence of Oswald ripening,we controlled the growth of nanocrystals by adding the core solution at high temperature,and the NaYF₄ nanocrystals with uniform morphology and size were synthesized successfully.?4?The NaYF₄:Yb³⁺,Tm³⁺/CdSe nanoheterostructures were synthesized successfully.Under 980 nm excitation,the luminescence of NaYF₄:Yb³⁺,Tm³⁺/CdSe nanoheterostructures at 797 nm was significantly enhanced and the UV and blue light was greatly reduced,which indicated that energy transform occurred between the NaYF₄:Yb³⁺,Tm³⁺ crystals and CdSe QDs.The 797 nm are located in the “optical window” of biological tissues.Therefore,the nanoheterostructures could have great potential in applications of bio-image...