documentclass[border=0.5pt]{standalone}
usepackage{ifluatex,ifxetex}
ifluatex
    usepackage{fontspec,luatex85}
else
   ifxetex
       usepackage{fontspec}
   else
       usepackage[T1]{fontenc}
   fi
fi
begin{document}
d{a} d{e} d{i} d{o} d{u}
end{document}