Size Dependence of the Magnetic and Optical Properties of Cd1-xMnxS Nanostructures Confined in Mesoporous Silica

Arrays of highly ordered Cd 1 - x Mn x S nanoparticles with x ranging from 0.01 to 0.2 and with lateral dimensions of 3, 6, and 9 nm were synthesized within mesoporous SiO 2 host structures of the MCM-41 and SBA-15 type. The hexagonal symmetry of these arrays (space group p 6 m ) and the high degree of order were confirmed by X-ray diffraction and transmission electron microscope studies. Physisorption measurements show the progressive filling of the pores of the SiO 2 host structures, while photoluminescence excitation (PLE) and electron paramagnetic resonance (EPR) studies confirm the good crystalline quality of the incorporated Cd 1 - x Mn x S guest species. The effects of the reduction of the lateral dimensions on the electronic properties of the diluted magnetic semiconductor were studied by PLE spectroscopy. Due to the quantum confinement of the excitons in the nanostructures an increase of the direct band gap with decreasing particle size as well as a stronger band gap bowing is observed. Analysis of the EPR line width and EPR intensity show that macroscopic magnetic properties such as the Curie−Weiss temperature are affected by the reduction of the lateral dimensions. The microscopic coupling between the Mn ions (e.g., the exchange constants J nn and J nnn ) is not altered to a first approximation.