Quantum Dots

Quantum dots are nanoparticles of a semiconductor material, traditionally chalcogenides (selenides or sulfides9 of metals like cadmium or zinc with a range from 2 to 10 nanometers in diameter.

Because of their small size, quantum dots display unique optical and electrical properties that are different in character to those of the corresponding bulk material. The most immediately apparent of these is the emission of photons under excitation, which are visible to the human eye as light. The wavelength of these photon emissions depends on the size of the particle rather than the material from which the quantum dot is made. The smaller the dot, the closer it is to the blue end of the spectrum, and the larger the dot, the closer to the red end. Dots can even be tuned beyond visible light into infra-red or into the ultra-violet.

CdS quantum dots cores vary between 380-480nm. The CdS Cores are composed of cadmium sulphide with carboxylic acids as capping agent, which provides enhanced longevity and stability.

Colour	Type	Absorption	Emission	FWHM
Colorless	CdS	380nm	370 - 390nm	≤30nm
Colorless	CdS	400nm	390 - 410nm	≤30nm
Pale Yellow	CdS	420nm	410 - 430nm	≤30nm
Yellow	CdS	440nm	430 - 450nm	≤30nm
Yellow	CdS	460nm	450 - 470nm	≤30nm
Yellow	CdS	480nm	470 - 490nm	≤30nm

   

In this paper the quantum dot prepared reported a pale yellow at plain sigth against a visible orange obtained during the first process, the difference in color, as mentioned, depends directly of the size of the particle. During the second process the reaction made to obtain the CdS quantum dots diminished the size of the particle, a visible change due to the color observed, to certify the diminishment of the particle’s size, a UV spectra was made to determine the real size of both particle, the one obtained during the first process and the second one.

Referencias:

http://www.nanocotechnologies.com/content/AboutUs/AboutQuantumDots.aspx por Nanoco Group PLC, consutado el 16 de octubre, 2012.