Quantum dot nanoparticles having enhanced stability and luminescence efficiency
Certain dithio-compounds have been found to be superior capping ligands for quantum dot (QD) nanoparticles. Example dithio-ligands include dithiocarbamate ligands. These strongly binding ligands are capable of coordinating to both positive and negative atoms on the surface of the nanoparticle. The ligands are bi-dentate and thus their approach to the QD surface is not as sterically hindered as is the approach of mono-dentate ligands. These ligands can therefore completely saturate the QD surface.
1. A method for preparing quantum dot (QD) nanoparticles comprising a plurality of dithiocarbamate capping ligands, the method comprising:
reacting a core nanoparticle with shell precursors in the presence of capping ligands to grow at least one semiconductor shell on the core, to form a core-shell nanoparticle having the capping ligands bound to an outermost surface thereof; and
exchanging at least a portion of the capping ligands with the dithiocarbamate capping ligands,
wherein the core is an InP or an InPZnS alloy-based core, and the shell precursors comprise zinc and sulfur or selenium.
2. The method recited in claim 1 further comprising etching the core prior to reacting the core with the shell precursors.
3. The method recited in claim 2 wherein hydrofluoric acid is used to etch the cores.
4. The method recited in claim 1 wherein the capping ligands are oleylamine.
5. The method recited in claim 1 wherein the capping ligands are myristic acid.
6. A method for preparing core-shell nanoparticles comprising a plurality of first dithiocarbonate capping ligands, the method comprising:
reacting a core nanoparticle with shell precursors in the presence of capping ligands to grow at least one semiconductor shell on the core, to form a core-shell nanoparticle having the capping ligands bound to an outermost surface thereof; and
exchanging at least a portion of the capping ligands with dithiocarbonate capping ligands,
wherein the core is an InP or an InPZnS alloy-based core, and the shell precursors comprise zinc and sulfur or selenium.
7. The method recited in claim 6 further comprising etching the core prior to reacting the core with the shell precursors.
8. The method recited in claim 7 wherein hydrofluoric acid is used to etch the cores.
9. The method recited in claim 6 wherein the capping ligands are oleylamine.
10. The method recited in claim 6 wherein the capping ligands are myristic acid.
11. The method recited in claim 6 , wherein the dithiocarbonate capping ligands used in the exchanging step are of the structure:
wherein R and R′ are selected from alkyl groups, aryl groups, functionalized alkyl group, functionalized aryl groups, and amphiphilic groups.
12. The method recited in claim 6 , wherein the dithiocarbonate capping ligands used in the exchanging step are zinc ethylxanthate capping ligands.