  By introducing new weighted vector fields as multipliers, we derive
quantitative pointwise estimates for solutions of defocusing semilinear wave
equation in $\mathbb{R}^{1+3}$ with pure power nonlinearity for all $1<p\leq
2$. Consequently, the solution vanishes on the future null infinity and decays
in time polynomially for all $\sqrt{2}<p\leq 2$. This improves the uniform
boundedness result of the second author when $\frac{3}{2}<p\leq 2$.
