Synthesis of deep-red-emitting CdSe quantum dots and general non-inverse-square behavior of quantum confinement in CdSe quantum dots

High-quality red-emitting CdSe quantum dots were synthesized by a microwave-assisted heating method in which the particle size was controlled mainly by changing reaction temperatures from 190 to 270 degrees C. The prepared samples were characterized by XRD, UV-Vis, photoluminescence, and TEM methods. The particle sizes range from 6.0 to 13.4 nm beyond the strong quantum confinement regime. The smallest quantum dots exhibit a zinc-blende structure while larger particles show a wurtzite structure. All the particles are isotropic in shape and exhibit well-defined photoluminescence despite their large sizes. By examining the optical properties of the red-emitting CdSe quantum dots, a definite quantification of size dependence of optical band gap with a clear empirical 1/d(1.25) scaling in a broad size range including smaller particles was established.