Studies on the synthesis and characterization of Zn_1−xCd_xS and Zn_1−xCd_xS:Mn²⁺ semiconductor quantum dots

Abstract

Quantum dots (3–4 nm) of Zn_{1− x} Cd _x S (both free of Mn²⁺ and with Mn²⁺ incorporated) were synthesized through a novel solvothermal-microwave irradiation technique. Detailed structural analysis of the Zn_{1− x} Cd _x S and Zn_{1− x} Cd _x S:Mn²⁺ (x = 0, 0.25, 0.5, 0.75 and 1) materials was carried out using powder X-ray diffraction technique. For all the compositions, the crystallite size was controlled to less than 1.5 nm. The optical energy gap for Zn_{1− x} Cd _x S was found to vary from 3.878 to 2.519 eV and for Zn_1−x Cd _x S:Mn²⁺ it varies from 3.830 to 2.442 eV when x is increased from 0 to 1. Overall, the optical energy gap could be tuned from a minimum of 2.442 eV to a maximum of 3.878 eV. DC conductivity analysis (from 40°C to 150°C) and electrical energy gap analysis for all the compositions were also performed. The dc conductivity for Zn_{1− x} Cd _x S solid solutions varies from 0.3840 × 10⁻¹⁰ to 8.7782 × 10⁻¹⁰ mho/m at 150°C and for Zn_{1− x} Cd _x S:Mn²⁺ it varies from 0.5751 × 10⁻¹⁰ to 9.8078 × 10⁻¹⁰ mho /m at 150°C (for x = 0 to x = 1). The method of synthesis and the results observed in this investigation may assist in the fabrication of optical devices when the required operational performance falls under the range observed in the study.

Keywords:

• microwave synthesis
• energy gap
• semiconductor
• quantum dot
• optical properties
• conductivity

Acknowledgements

One of the authors (C.K. Mahadevan) thanks the Council of Scientific and Industrial Research (CSIR), New Delhi for the grant of a Major Research Project. We also thank Mr. Periyasamy (BHU, Varanasi) and Mr. P. Gurusamy (NIIST, Thiruvananthapuram) for their helpful discussions in the EDAX and XRD analysis.