Optical Properties of Selenium Quantum Dots Produced with Laser Irradiation of Water Suspended Se Nanoparticles

• Published in: Journal of physical chemistry. C Vol. 114; no. 41; pp. 17374 - 17384
• Main Authors: Singh, S. C, Mishra, S. K, Srivastava, R. K, Gopal, R
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.10.2010
• Subjects: C: Nanops and Nanostructures
• DOI: 10.1021/jp105037w
• ISSN: 1932-7447

Semiconductor quantum dots (QDs) and their assemblies have shown potential research interest due to their size dependent optical and electronic properties. Laser irradiation of larger sized semiconductor nanoparticles (NPs) suspended into liquid media is an easy, quick, versatile, environmental friendly, and rapidly growing method for the synthesis of QDs through melting/vaporization and fragmentation mechanisms. Most of the available reports in this field are related to the laser induced modification of shape, size, and morphology of noble metal nanoparticles, while only few exist for semiconductors. Synthesis of selenium QDs using laser induced melting/vaporization of water suspended selenium NPs of larger size and studies of their irradiation time or size dependent optical properties are subjects of current investigation. The fundamental wavelength of a pulsed nanosecond Nd:YAG laser is used for the irradiation of water suspended 69 nm average sized NPs for different times of irradiation. UV−visible absorption, XRD, TEM, and PL spectroscopic methods are utilized for the characterization of as synthesized QDs and raw NPs. Size and hence optical properties of produced selenium QDs are found to be highly dependent on the time of irradiation. The size of the produced selenium QDs follows a second order exponential decay function of irradiation time, while the rate of size reduction, da/dt, is directly dependent on the diameter, a, of the instantaneous QDs, very similar to the radioactive decay model. Laser irradiation causes transformation of β-Se NPs of 69 nm diameter to α-Se QDs of different sizes depending on the time of irradiation. We have achieved a minimum 2.74 ± 2.32 nm diameter of selenium QDs for 15 min laser irradiation and reported that almost 3.75 ± 0.15 nm size may be the quantum confinement limit for Se QDs. Surface defect density of the selenium QDs increases, while defect/electron trap level energy decreases, with the time of laser irradiation.