  It is well known that if a function $f$ satisfies $$\|f(x) e^{\pi \alpha
|x|^2}\|_p + \| \widehat{f}(\xi) e^{\pi \alpha |\xi|^2} \|_q<\infty
\qquad\qquad\qquad(*)$$
  with $\alpha=1$ and $1\le p,q<\infty$, then $f\equiv 0.$
  We prove that if $f$ satisfies $(*)$ with some $0<\alpha<1$ and $1\le p,q\leq
\infty$, then $$ |f(y)|\le C
  (1+|y|)^{\frac{d}{p}}
  e^{- \pi \alpha |y|^2}, \quad y\in \mathbb{R}^d, $$ with $ C=C(\alpha,d,p,q)$
and this bound is sharp for $p\neq 1$. We also study a related uncertainty
principle for functions satisfying $\;\;\displaystyle\|f(x)|x|^m\|_p+
\|\widehat{f}(\xi)|\xi|^n\|_q <\infty.$
