  In this paper we establish $L^p$-boundedness properties for Laplace type
transform spectral multipliers associated with the Schr\"odinger operator
$\mathcal{L}=-\Delta +V$. We obtain for this type of multipliers pointwise
representation as principal value integral operators. We also characterize the
UMD Banach spaces in terms of the $L^p$-boundedness of the imaginary powers
$\mathcal{L}^{i\gamma}$, $\gamma \in \mathbb{R}$, of $\mathcal{L}$.
