In Baraka's paper [2], he obtained the Littlewood-Paley characterization of
Campanato spaces $L^{2,\lambda}$ and introduced $\mathcal {L}^{p,\lambda,s}$
spaces. He showed that $\mathcal
{L}^{2,\lambda,s}=(-\triangle)^{-\frac{s}{2}}L^{2,\lambda}$ for
$0\leq\lambda<n+2$. In [7], by using the properties of fractional Carleson
measures, J Xiao proved that for $n\geq2$, $0<\alpha<1$.
$(-\triangle)^{-\frac{\alpha}{2}}L^{2,n-2\alpha}$ is essential the
$Q_{\alpha}(\mathbb{R}^n)$ spaces which were introduced in [4].