Authors: S.P. Singh, O. Perales-Perez, M.S. Tomar, A. Parra-Palomino and A. Ruiz-Mendoza
Affilation: University of Puerto Rico, Puerto Rico
Pages: 29 - 32
Keywords: room-temperature synthesis, characterization, monodisperse, nanocrystals, doped-ZnO
We present here the results of our current efforts on size-controlled synthesis of bare and Mn- and Co-doped ZnO nanocrystals. Stable suspensions of these materials were produced in ethanol solutions at room-temperature. XRD characterization of the products verified the fast formation of ZnO nanocrystals. The actual incorporation of Mn and Co into the ZnO host was suggested by XRD analyses; however, their presence delayed the formation of the host structure. HRTEM analyses revealed the high monodispersity of the 5-8 nm nanocrystals. UV-visible and photoluminescence measurements evidenced not only the nanocrystalline nature of the samples but also the continuous growth of the nanocrystals when aged in their mother liquors. The estimated band gap energy of non-aged ZnO nanocrystals was 3.72eV and decreased down to 3.46eV after 48 hours of aging, when no further growth was observed. The UV-visible analyses also confirmed the inhibition of crystal growth when the nanocrystals were coagulated by n-heptane and redispersed in fresh ethanol. SQUID measurements indicated that as-synthesized doped ZnO nanocrystals were paramagnetic at room-temperature in contrast with the diamagnetic nature of bare ZnO. The effect of thermal treatment of nanocrystals and the dependence of magnetic properties with crystal size will also be discussed.