On the representation of an imaginary quadratic integer in two different bases

Let $(\alpha,\mathcal{N}_{\alpha})$ and $(\beta,\mathcal{N}_{\beta})$ be two canonical number systems for an imaginary quadratic number field $K$ such that $\alpha$ and $\beta$ are multiplicatively independent. We provide an effective lower bound for the sum of the number of non-zero digits in the $\alpha$-adic and $\beta$-adic expansions of an algebraic integer $\gamma\in\mathcal{O}_K$ which is an increasing function of $|\gamma|$. This is an analogue of an earlier result due to Stewart on integer representations.