Journal of Physical Chemistry & Biophysics
Open Access
ISSN: 2161-0398
ISSN: 2161-0398
V Masilamani, Saradh Prasad, K H Ibnaouf, and M S AlSalhi
Posters-Accepted Abstracts: J Phys Chem Biophys
A number of reports have been published on laser from quantum dot nano structure by current injection. In contrast, we have recently obtained amplified spontaneous emission (ASE) and laser from CdSe/ZnS quantum dot (QDs) in a colloidal liquid. A Third harmonic of Nd: YAG laser (355nm) was used to produce laser-induced fluorescence (LIF) at 605 nm with a spectral width of 20 nm [full width at half maximum (FWHM)]. When the pump pulse energy went up to 20mJ and focusing were carefully optimized, an ASE at 610 nm with a spectral width of �?λ= 8 nm (FWHM) could be obtained. The beam was directional with a divergence of 10 milli radians (mrad); but the conversion efficiency was about 0.05%. This is perhaps one of the very few reports on laser from nano structures. It is important to draw attention to the following facts: (a) ASE could not be obtained by transverse excitation as in the case of conventional laser dyes such as fluorescein or coumarin or more recent conjugated polymers MEH_PPV. (b) Optical gain of the QDs appears to be quite inferior to conventional to conventional laser dyes like RB or conjugated polymer like MEH-PPV, though the quantum yield of fluorescence are comparable. This is because QDs do not go into solution in any of the solvents; they remain only as suspensions, with a strong tendency to go to precipitation after a certain level of concentrations. Because of this, most of the photons incident upon the QD get scattered; only a small number of them get absorbed and re-emitted as fluorescence, albeit efficiently. In order to improve the lasing characteristic of QD, one may need to do energy transfer process (like He �?? Ne or N2 CO2 laser). For example, coumarin dye laser pumped by the same frequency tripled Nd:YAG could provide better laser efficiency. More importantly new techniques of dissolving high concentrations of the QD in suitable liquid are being tried by other group. Nevertheless, it appears that the optically pumped QD laser would not be comparable to RB or MEH-PPV laser in terms of efficiency.