Nanocrystals with high extinction coefficients and methods of making and using such nanocrystals

Abstract

A population of bright and stable nanocrystals is provided. The nanocrystals include a semiconductor core and a thick semiconductor shell and can exhibit high extinction coefficients, high quantum yields, and limited or no detectable blinking.

1 .- 9 . (canceled) 
     
     
         10 . A population of nanocrystals, wherein each nanocrystal_in the population comprises:
 a semiconductor core; and   a semiconductor shell disposed on the semiconductor core, wherein the population exhibits an absorbance intensity, wherein a ratio of the absorbance intensity of the population measured at an excitation wavelength of 405 nm to the absorbance intensity of the population measured at the band edge absorbance wavelength (A 405 nm /A band-edge ) or at an excitation wavelength that is 25 nm less than the band edge emission wavelength (A 405 nm /A (λem-25 nm)  is 20 or greater.   
     
     
         11 . The population of  claim 10 , wherein A 405 nm /A band-edge  or A 405 nm /A (λem-25 nm)  is 150 or less. 
     
     
         12 .- 13 . (canceled) 
     
     
         14 . The population  claim 10 , wherein the population has a maximum fluorescence emission wavelength in the visible portion of the electromagnetic spectrum below the red spectral region. 
     
     
         15 . The population of  claim 10 , wherein the population has a maximum fluorescence emission wavelength less than about 620 nm. 
     
     
         16 . The population of  claim 10 , wherein the population has a maximum fluorescence emission wavelength in the red spectral region. 
     
     
         17 .- 22 . (canceled) 
     
     
         23 . The population of nanocrystals of  claim 10 , wherein the population:
 exhibits an extinction coefficient of 3,000,000 cm −1 M −1  or greater when measured at an excitation wavelength of 405 nm.   
     
     
         24 .- 50 . (canceled) 
     
     
         51 . The population of  claim 23 , wherein the extinction coefficient is about 30,000,000 cm −1 M −1  or less. 
     
     
         52 . The population of nanocrystals of  claim 10 , wherein each nanocrystal in the population has a nanocrystal volume to core volume ratio (V core+shell /V core ) of 5:1 or greater. 
     
     
         53 . The population of  claim 52 , wherein the average core volume is about 100 nm 3  or less. 
     
     
         54 . The population of  claim 52 , wherein the average nanocrystal volume is about 150 nm 3  or greater. 
     
     
         55 . The population of  claim 10 , wherein the semiconductor shell comprises an alloyed semiconductor material. 
     
     
         56 . The population of  claim 10 , wherein the core and/or shell comprises a Group II-VI, a Group II-VI-VI, or a Group semiconductor material. 
     
     
         57 . The population of  claim 10 , wherein the semiconductor shell comprises Cd, S, Se, Zn, or a combination thereof. 
     
     
         58 . The population of  claim 10 , wherein the semiconductor shell comprises a semiconductor material selected from ZnS, CdS, CdZnS, CdSeZn, ZnSeS, CdSeZnS and combinations thereof. 
     
     
         59 . The population of  claim 10 , wherein the population has a maximum fluorescence emission wavelength in the near-IR spectral region. 
     
     
         60 . A photovoltaic or light-emitting device, comprising the population of nanocrystals of  claim 10 . 
     
     
         61 . A method of detecting a target species in a sample, comprising:
 contacting a sample suspected of containing a target species with the population of nanocrystals of  claim 10  for a time sufficient to bind the target species to at least one nanocrystal in the population; and   monitoring fluorescence emission to detect the presence of the at least one nanocrystal.