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Based on density functional theory (DFT), the effects of scandium (Sc) doping and oxygen vacancy ([V.sub.O]) on the electronic states and optical properties of monoclinic BiV[O.sub.4] (m-BiV[O.sub.4]) are investigated. The generalized gradient approximation plus U (GGA+U) method is adopted during the calculation of the electronic properties to compensate for the limitations of the DFT method. The ideal m-BiV[O.sub.4] has a direct band gap of 2.400 eV, and if Bi in m-BiV[O.sub.4] is substituted by Sc ([sub.sub.Sc-Bi]), the direct band gap will be reduced to 2.393 eV. However, if V is replaced by Sc ([sub.sub.Sc-V]) as well as oxygen vacancy induced ([sub.sub.Sc-V]+[V.sub.O]), the band gap will become indirect with values of 1.913 and 2.198 eV, respectively. The reduction capability is in the sequence of [sub.sub.Sc-Bi] > ideal > [sub.sub.Sc-V]+[V.sub.O] > [sub.sub.Sc-V], while the oxidation capability is in the order of ideal > [sub.sub.Sc-Bi] > [sub.sub.Sc-V]+[V.sub.O] > [sub.sub.Sc-V]. The [[epsilon].sub.1](0) of the ideal, [sub.sub.Sc-Bi], [sub.sub.Sc-V], and [sub.sub.Sc-V]+[V.sub.O] defective m- BiV[O.sub.4] are 8.290, 8.293,12.791, and 8.285, respectively. The optical absorptions of ideal and [sub.sub.Sc-Bi] m-BiV[O.sub.4] show anisotropy and they are nearly independent of the defect concentration. [sub.sub.Sc-V] m-BiV[O.sub.4] exhibits stronger absorption than the other three semiconductors. The absorptions of [sub.sub.Sc-V]+[V.sub.O] m-BiV[O.sub.4] vary widely with the defect concentrations, where 3.906% defect concentration of m-BiV[O.sub.4] has the strongest absorption. The estimated optical band gaps [E.sup.opt.sub.g] are smaller than [E.sub.g] for ideal and defective m-BiV[O.sub.4]. Key words: doping, vacancy, electronic states, optical properties, m-BiV[O.sub.4]. Sur la base de la theorie de la fonctionnelle de densite (DFT), nous examinons les effets du dopage au scandium (Sc) et des lacunes en oxygene ([V.sub.O]) sur les etats electroniques et les proprietes optiques du compose monoclinique BiV[O.sub.4] (m-BiV[O.sub.4]). L'approche GGA+U est adoptee dans le calcul des proprietes electroniques afin de compenser les limitations de la methode TFD. Le m-BiV[O.sub.4] ideal a un gap direct de 2,400 eV et si le Bi est remplace par un Sc, ([sub.sub.Sc-Bi]), le gap direct est reduit a 2,393 eV. Cependant, si le V est remplace par un Sc ([sub.sub.Sc-V]), aussi bien qu'avec lacune en oxygene ([sub.sub.Sc-V]+[V.sub.O]), alors le gap devient indirect avec des valeurs de 1,913 eV et 2,198 eV respectivement. La capacite de reduction suit la sequence suivante, [sub.sub.Sc-Bi] > ideal > [sub.sub.Sc-V]+[V.sub.O] > [sub.sub.Sc-V], pendant que la capacite oxydante suit la sequence suivante, ideal > [sub.sub.Sc-Bi] > [sub.sub.Sc-V]+[V.sub.O] > [sub.sub.Sc-V]. La valeur de [[epsilon].sub.1](0) pour chacun des cas suivants, ideal, [sub.sub.Sc-Bi], [sub.sub.Sc-V] et [sub.sub.Sc-V]+[V.sub.O], est calculee etre 8,290, 8,293,12,791 et 8,285 respectivement. L'absorptions optique des cas ideal et [sub.sub.Sc-Bi] m-BiV[O.sub.4] montre une anisotropie et est pratiquement independantes des concentrations de defauts. [sub.sub.Sc-V] mBiV[O.sub.4] montre une plus forte absorption que les trois autres semi-conducteurs. Les absorptions de [sub.sub.Sc-V]+[V.sub.O] mBiV[O.sub.4] varient evidemment avec la concentration de defauts, la plus forte absorption se presentant a 3,906% de concentration de defauts de mBiV[O.sub.4]. Les gaps optiques estimes [E.sup.opt.sub.g] sont plus petits que [E.sub.g] pour tous les cas de m-BiV[O.sub.4], ideal et avec defauts. [Traduit par la Redaction] Mots-cles : dopage, lacune, etats electroniques, proprietes optiques, mBiV[O.sub.4]., 1. Introduction Due to the urgent issues of environmental pollution and energy shortage, many efforts have been done to explore the materials for solar energy conversion and organic pollutant degradation [...]