Size-dependent properties of CdSe quantum dots

Temperature dependences of the magnetic susceptibility $\ensuremath{\chi}$ and heat capacity ${C}_{p}$ of CdSe quantum dots with size $d=2.8$, 4.1, and 5.6 nm are compared to those of bulk CdSe to determine the size-dependent effects. With decreasing size $d$, the following effects are observed: (i) room temperature optical absorption shows a blueshift of the band gap; (ii) room temperature x-ray diffraction show wurtzite structure but with smaller lattice constants; (iii) magnetic susceptibility changes from negative (diamagnetic) for the bulk to positive $\ensuremath{\chi}$ with magnitude increasing with decreasing $d$; and (iv) the Sommerfeld constant $\ensuremath{\gamma}$ determined from the ${C}_{p}∕T$ vs ${T}^{2}$ data increases. Possible explanations for these size-dependent properties are presented.