fulltext - J Fluoresc(2007 17:607611 DOI...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
SHORT COMMUNICATION Fluorescence Enhancement of CdSe Q-Dots with Intense Femtosecond Laser Irradiation D. Narayana Rao N. Venkatram Received: 5 January 2007 /Accepted: 23 July 2007 /Published online: 17 August 2007 # Springer Science + Business Media, LLC 2007 Abstract Effects of intense femtosecond (fs) laser irradia- tion on the optical properties of cadmium selenide (CdSe) nanocrystals are studied. We present the changes in emission and absorption of laser (800 nm, 110 fs, Ti Sapphire) irradiated CdSe nanocrystals dispersed in dimeth- ylformamide (DMF). It is observed that the absorbance of CdSe nanocrystals capped with trioctylphosphine (TOP) increases with the number of laser pulses. The trap state luminescence intensity of these crystals degrades, whereas the band edge luminescence intensity shows an increase as a function of the fs laser irradiation. We also report strong two photon absorption and reduction in the trap state luminescence intensity after irradiation with the laser pulses. Keywords Cadmium selenide nanocrystals . Band edge emission . Trap state emission . Two photon excited fluorescence Introduction In recent years, interest in the synthesis, characterization, and application of colloidal quantum dot semiconductor materials has grown markedly [ 1 ]. Nanocrystals of CdSe are by far the most studied system among all the semi- conducting nanocrystals. Colloidal quantum dots (QDs), also known as semiconductor nanocrystals, are synthesized by chemical routes and dispersed in suitable solutions. Nanocrystals smaller than the Bohr radius of the particular semiconductor demonstrate unique optical properties due to the effects of three dimensional quantum confinement. Smaller the crystal, greater is the confinement potential (roughly corresponding to particle in a spherical box); this results in a broadening of the band gap that is inversely proportional to the particle size. The bulk CdSe has a direct band gap of 1.74 eV at 300 K, and the typical Bohr exciton diameter of CdSe is around 10.6 nm; consequently, CdSe nanocrystals in the size of <11 nm show sizable quantum confinement effects with remarkably different optical properties. The changes in the properties of nanocrystals are driven mainly by two factors, namely the increase in the surface to volume ratio, and drastic changes in the elec- tronic structure of the material due to quantum mechanical effects with decreasing crystal size. In the QDs, photoluminescence occurs when an electron is excited into the conduction band levels, creating an electron-hole pair which recombines to emit a photon. The broader the band gap, more energetic is the photon and hence bluer will be the emission wavelength. Depending upon the material, QDs can be tuned to emit at different visible or infrared wavelengths by controlling their sizes [ 2 ]. QDs have several proven and potential applications as biosensors; these are used as fluorescent dyes [ 3 9 ]i n
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/30/2010 for the course MATH Math 117 taught by Professor Notsure during the Spring '10 term at École Normale Supérieure.

Page1 / 5

fulltext - J Fluoresc(2007 17:607611 DOI...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online