Bulk Zn0.95TM0.05O ( , Mn, Fe, Co, and Ni) were synthesized by the standard ceramic method and explored for variation in their band gap energies using Diffuse Reflectance Spectroscopy in the ultraviolet-visible region. Phase quantification and compositional studies were performed using Rietveld analysis of the X-Ray Diffraction patterns, Scanning Electron microscopy, and Energy Dispersive X-Ray Analysis. Due to 3d transition ion doping, the samples have brilliant colors, and the absorption edge of Zn0.95TM0.05O was found to shift towards the visible and ultraviolet-visible region. The blue and red shifts in band gaps observed for various transition metal ion-doped ZnO are discussed. 1. Introduction Zinc Oxide (ZnO), a direct wideband gap semiconductor, has been of great interest for application in optical devices such as blue-violet and UV-light emitting diodes and laser diodes [1, 2]. Recently, ZnO is alloyed with various “3d” transition metal (TM) ion for exploring its applicability in the field of SPINTRONICS (Spin Transport Electronics) [3–7]. Theoretical simulation of electronic structures of 3d transition metal ion- doped ZnO has been reported by Toyoda et al. [8]. The ferromagnetic behavior and high transition temperature of the wide band gap semiconductors have wide controversy. Theory of spinodal decomposition for the observed magnetic behavior in wide band gap semiconductors has been framed recently by abinitio electronic structure calculations [9–11]. Owing to the transparency of ZnO, “transparent magnets” [4] exhibiting a number of unique magnetic, magneto-optical, and magnetotransport properties are also expected. Oxide-based Diluted Magnetic Semiconductors (DMSs) are superior to their III–V counterparts, and a number of review articles were published on them [12–15]. To exploit materials for optoelectronic applications, it is essential to tune the optical band gap which can be done by way of doping with various “3d” transition metal ions apart from introducing spin degree of freedom into the ZnO matrix. Band gap tailoring at the ultraviolet end and visible region of the solar spectrum is of considerable interest for large area optical coatings. As most of the optical studies on ZnO DMS were on thin films only, the present study is aimed at measuring directly the band gap energies of bulk Zn0.95TM0.05O (TM = Cr, Mn, Fe, Co, & Ni) using Diffuse Reflectance Spectrocopy (DRS) which is particularly suitable for the determination of absorption edges of powdered materials. Bulk Zn0.95TM0.05O (TM = Cr, Mn, Fe, Co & Ni) prepared by ceramic method
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