The authors proposed a simple empirical method to quantitatively calculate the impurity energy levels of transition metal ions doped in different host inorganic crystals. Linear relationships were obtained between the impurity energy level and the reciprocal of the strength of chemical bonds between the impurity cations and anions of host crystals which was defined in terms of the basic atom and bond parameters such as electronegativity, bond length and the number of valence electrons. Based on these linear relationships, the authors calculated the impurity energy levels of transition metal ions in rutile TiO 2 , III-V and II-VI semiconductors and some perovskite oxides, which are in good agreement with the available experimental values. The quantitative relationships established in current work can serve as an effective tool to predict the impurity energy levels, which will provide guidance in tuning the functional properties of inorganic crystal materials.

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