Nanoscale Res Lett (2010) 5:1289–1294 1293 Fig. 5 PL spectra of ZnFe2O4 nanowire arrays within AAO tem- plates measured at RT, and the image captured by camera indicates that the sample gives out blue-violet light is shown in the inset Fig. 6 a The UV–vis absorption spectra b plots of ðahmÞ1=2 and (c) ðahmÞ2 vs hm for ZnFe2O4 nanowire arrays our result. At the same time, the image captured by camera indicates that the sample gives out blue-violet light, which is corresponding to the PL spectrum result. ZnFe2O4 has been known to have the strong absorption in the UV–vis range [38–40]. As shown in Fig. 6, the ZnFe2O4 nanowire arrays have the strong band edge absorption in the wave- length region of B700 nm. The optical band gap Eg can be estimated from absorption coefﬁcient (a) using the Tauc relation ahv ¼ Aðhm EgÞ q where A is a constant that depends on the transition prob- ability, hv is the energy of incident photon, and q is an index that characterizes the optical absorption process [41]. It is well known that direct and indirect band gap energy for the semiconductor nanostructures can be obtained from the intersection of linear ﬁts of ðahmÞ1=q versus hv plots for q = 1/2 and 2 on the x-axis. Here, the estimated values of the direct and indirect band gaps are about 2.23 and 1.73 eV for preferred oriented ZnFe2O4 nanowire arrays, respectively (shown in Fig. 6b and c). Improved optical properties of the ZnFe2O4 nanomaterials are expected, and these aspects need further investigation. Conclusion In summary, arrays of ZnFe2O4 nanowires with diameters of about 16 nm were successfully fabricated by electro- deposition of Zn2? and Fe2? into AAO templates and post- oxidation annealing in atmosphere. The results of XRD and HRTEM exhibit that the nanowires have the bcc structure with [110] as the texture direction along the nanowire axis. The preferred orientation and shape anisotropy of the nanowire arrays makes the ZnFe2O4 nanowire arrays to exhibit the uniaxial magnetic anisotropy with the easy magnetization direction along the nanowire axes. The optical properties show ZnFe2O4 nanowire arrays give out blue-violet light, and the optical band gap Eg is estimated from absorption coefﬁcient. Further investigation into magnetic and optical properties of the ZnFe2O4 nanoma- terials is in progress. Acknowledgments This work is supported by National Science Fund for Distinguished Young Scholars (Grant No. 50925103), The Keygrant Project of Chinese Ministry of Education (Grant No. 309027) and The Fundamental Research Funds for the Central Uni- versities (Grant No. Lzujbky-2009-162). Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which per- mits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References 1. R.C.V. Gopal, S.V. Manorama, V.J. Rao, J. Mater. Sci. Lett. 19, 775 (2000) 2. Z. Jiao, M.H. Wu, J.Z. Gu, Z. Qin, IEEE Sens. J. 3, 435 (2003) 3. X.S. Niu, W.P. Du, W.M. Du, Sens. Actuators B 99, 405 (2004) 4. X.F. Chu, X.Q. Liu, G.Y. Meng, Sens. Actuators B 65, 64 (2000) 5. G.G. Liu, X.Z. Zhang, Y.J. Xu, X.S. Niu, L.Q. Zheng, X.J. Ding, Chemosphere 55, 1287 (2004) 6. M. Sultan, R. Singh, J. Appl. Phys. 105, 07A512 (2009) 7. F.F. Liu, X.Y. Li, Q.D. Zhao, Y. Hou, X. Quan, G.H. Chen, Acta Mater. 57, 2684 (2009) 8. V. Sepelak, M. Zatroch, K. Tkacova, P. Petrovic, S. Wibmann, K.D. Becker, Mater. Sci. Eng. A. 22, 226 (1997) 123