Colloidal Nanocrystals Ensembles with Narrow Linewidth Band Gap Photoluminescence and Methods of Synthesizing Colloidal Semiconductor Nanocrystals

Abstract

A method of synthesizing colloidal semiconductor nanocrystals involves contacting a source of at least one semiconductor cation element (Group 11-14, more preferably Group 12-14, more preferably 12 or 14, more preferably Cd, Zn, Hg or Pb, most preferably Cd) with a source of at least one Group 15, or 16 element in the presence of a ligand forming compound containing a carboxylic acid moiety in a reaction medium comprising a solvent that is substantially noncoordinating with respect to the at least one cation, the ligand forming compound and the source of at least one cation element having a molar ratio of 1:1 or less. The cation element source is preferably bonded to two low carbon acids. Some of the low carbon acids are substituted with the ligand forming compound to produce a cation precursor that is more soluble in the noncoordinating solvent. The method produces novel ensembles of colloidal semiconductor nanocrystals that have narrow linewidth absorption and bandgap photoluminescence spectra indicating that the colloidal semiconductor nanocrystals are of substantially a single size. The single size families are produced for CdSe, CdTe, CdS, CdSeTe, and CdP.

1 . A process of synthesizing colloidal semiconductor nanocrystals comprising contacting a source of at least one semiconductor cation element with a source of at least one semiconductor anion element in the presence of a ligand forming compound containing a carboxylic acid moiety in a reaction medium comprising a solvent for the ligand that is at least substantially noncoordinating with respect to the cation, the ligand forming compound and the at least one cation element having a molar ratio of substantially 1:1 or less. 
     
     
         2 . The process according to  claim 1 , wherein the source of at least one cation element and the source of at least one anion element provides precursor cations bound to acetate and precursor anions bound to longer chain ligands, or vice versa, whereby both long and short chain ligands are bound to each semiconductor nanocrystal. 
     
     
         3 . The process according to  claim 1 , wherein the solvent is 1-octadecene. 
     
     
         4 . The process according to  claim 1  wherein the ligand forming compound is a C 8 -C 34  organic acid. 
     
     
         5 . The process according to  claim 1  wherein the ligand forming compound is a saturated fatty acid having a chemical formula CH 3 (CH 2 ) n COOH, wherein n is an integer from 6 to 28. 
     
     
         6 . The process according to  claim 1 , wherein the at least one cation element is in Group 11, 12, 13 or 14 of the periodic table, and the at least one anion is in Group 15, 16 or 17 of the periodic table. 
     
     
         7 . The process according to  claim 6 , wherein the at least one cation element is in Group 12, 13 or 14 of the periodic table, and the at least one anion is in Group 15, or 16 of the periodic table. 
     
     
         8 . The process according to  claim 6 , wherein the at least one cation element is in Group 12 or 14 of the periodic table, and the at least one anion is in Group 15 or 16 of the periodic table. 
     
     
         9 . The process according to  claim 1 , wherein the source of at least one Group 12 element is cadmium acetate dihydrate. 
     
     
         10 . The process according to  claim 1 , wherein the reaction medium is heated to a temperature within a range of from 90° C. to 290° C. for a length of time and then cooled to arrest growth of the nanocrystals. 
     
     
         11 . The process according to  claim 1 , wherein the at least one cation is Cd, and the source of anion element is: elemental Se; elemental S; elemental Te; a mixture of elemental Se and elemental Te, and the Se and Te are first solubilized in trioctylphosphine before contacting the source of at least one cation element; bis(trimethylsilyl) sulfide; and thioacetamide. 
     
     
         12 . The process according to  claim 1 , wherein the contacting is performed in vacuo. 
     
     
         13 . The process according to  claim 1 , wherein the reaction medium is heated for a first length of time at a first temperature in vacuo and then heated to a higher second temperature under an inert atmosphere for a second length of time. 
     
     
         14 . The process according to  claim 1 , wherein a dispersant is used to help solubilize the source of anion element. 
     
     
         15 . The process according to  claim 1 , wherein the colloidal semiconductor nanocrystals are bandgap photoluminescent. 
     
     
         16 . The process according to  claim 15  wherein the colloidal semiconductor nanocrystals are substantially all of a single size. 
     
     
         17 . The process according to  claim 15  wherein the colloidal semiconductor nanocrystals have collectively a bandgap photoemission linewidth of 10±7 nm.