Magnesium-based coatings for nanocrystals

Abstract

Semiconductor nanocrystal compositions comprising magnesium containing shells and methods of preparing them are described. The compositions provide strong emission in the blue and green wavelengths as well as chemical and photostability that have not been achieved with conventional shell materials.

1 .- 20 . (canceled) 
     
     
         21 . A process for making a photostable nanocrystal comprising the steps of:
 i) providing a first core/shell nanocrystal;   ii) dispersing the nanocrystal in a reaction mixture containing a magnesium material; and   iii) heating the reaction mixture with the nanocrystal to a temperature of at least about 120° C.;
 to provide a photostable nanocrystal having better photostability than the first core/shell nanocrystal. 
   
     
     
         22 . The process of  claim 21 , wherein the photostable nanocrystal loses less than 10% of its initial emission intensity under conditions where the first core/shell nanocrystal would lose 20% of its initial emission intensity. 
     
     
         23 . The process of  claim 21  or  claim 22 , wherein the reaction mixture comprises an alkylphosphinic acid, a trialkylphosphine, or a trialkylphosphine oxide, or a mixture of at least two of these materials. 
     
     
         24 . The process of  claim 21 , wherein the photostable nanocrystal loses less than 10% of its initial emission intensity under conditions where the first core/shell nanocrystal would lose 40% of its initial emission intensity. 
     
     
         25 . The process of  claim 21 , wherein the core of the first core/shell comprises ZnSe. 
     
     
         26 . The process of  claim 21 , wherein the core of the first core/shell comprises ZnCdSe. 
     
     
         27 . The process of  claim 26 , wherein the ratio of Zn to Cd is at least about 1. 
     
     
         28 . The process of  claim 26 , wherein the amount of Cd in the core provides a core having a largest dimension of about 6 nm and a fluorescence color in the blue or green region of the visible spectrum. 
     
     
         29 . The process of  claim 26 , wherein the amount of Cd in the core provides a core having a largest dimension of about 6 nm and a fluorescence emission maximum at a wavelength above 500 nm. 
     
     
         30 . The process of  claim 21 , wherein the shell of the first core/shell nanocrystal comprise ZnS. 
     
     
         31 . The process of  claim 21 , wherein the magnesium material is a magnesium alkylcarboxylate. 
     
     
         32 . The process of  claim 31 , wherein the magnesium alkylcarboxylate is magnesium acetate. 
     
     
         33 . The process of  claim 21 , wherein the reaction mixture comprises at least one material selected from a trialkylphosphine, a trialkylphosphine oxide, an alkylamine, and an alkylphosphinic acid. 
     
     
         34 . The process of  claim 33 , wherein the reaction mixture comprises trioctylphosphine. 
     
     
         35 . The process of  claim 21 , wherein the step of heating the reaction mixture with the nanocrystal comprises heating the mixture to a temperature between about 150° C. and about 250° C. 
     
     
         36 . The process of  claim 35 , wherein the step of heating the reaction mixture with the nanocrystal comprises heating the mixture for between about 0.5 hr and about 4 hr. 
     
     
         37 . A photostable nanocrystal made by the process of  claim 21 . 
     
     
         38 . A nanocrystal comprising a semiconductor core and a shell, wherein the shell comprises Mg.