Hi,
Not sure why are you again are you handling the server click event here(also are you sure there is an attribute named 'onserverclick' i m not thinking so), because simply setting the 'href' attribute value should work for the anchor tags.
Please remove handler being added as [onserverclick="lnk_clicked"].
Else if it is not working you can try with adding below attribute value like
target="_blank"
Hope this will be of help.