PHP is executed at the server-side and thus does not know about clients, browsers or windows of those browsers.
Some options though:
Close button
<?php
echo "<BUTTON onclick='window.close();'>CLOSE</BUTTON>";
<a onclick='window.close();' style='cursor:pointer;' >Close</a>
?>Close using java script
<script language=JavaScript>
window.close();
</script> <a class="GoBackButton" href="javascript:window.close();"><div class="GoBackButton">Go Back</div></a>Feel free to comment if you can add help to this page or point out issues and solutions you have found. I do not provide support on this site, if you need help with a problem head over to stack overflow.