I have tried several times to synthesize upconversion nanoparticles using a thermal decomposition method but have not yet been successful with my synthesis.
I dissolve lanthanide oxides in 50% aqueous trifluoroacetic acid at 80 °C then evaporate to dryness at 60 °C. I then add sodium trifluoroacetate, 1-octadecene (90% purity), and oleic acid (90% purity) and heat the solution to 120 °C under vacuum with stirring for 30 min, obtaining a clear, light yellow solution. I then switch to argon and heat the solution to 320 °C for 1 h. Above 300 °C, white smoke appears and circles around in the flask (at the same time that there occurs what I think is bumping) whenever a drop of condensed liquid falls back into the solution. After cooling down to room temperature, I end up with a clear, golden solution. Centrifuging results in white product but the obtained upconversion of these particles when exciting with 500 mW 980 nm laser is barely detectable. In addition, a 1wt% solution is translucent/cloudy rather than transparent/clear like what I've seen in other papers.
Is the white smoke a sign that there are still residual impure solvents that I haven't boiled off? Would increasing the heating time at 120 °C solve this or is there another better way? Are there any other possible mistakes I might be making that's causing me to end up with white product that has poor upconversion?
Thanks for your help!
Simplify your synthesis. You have to understand it.
Lanthanide acetate react with oleic acid molar ratio 1:4.2 in 1-octadecene 10 ml under 320 0C. The formed lanthanide carboxylate decompose 60 min.
Best regards.
In addition, you mentioned making a 1% w/v solution of your formed nanoparticles. If the colloidal dispersion is quite apparent compared to your reference(s) then perhaps agglomeration is at issue from the drying stage. Have you taken steps to mitigate that effect when resuspending your nanoparticles? Filtering/dialysis and ultrasonication for extended periods would be helpful in this regard.
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