php - save data to xml file -

i generating charts using fusioncharts. using xml file generate charts.but not able generate xml file.

$colone ="";  $open_vals = "<chart  caption='referrals' labeldisplay='rotate' showborder='0' showlegend ='1' showplotborder='0' bgcolor = '#ffffff' plotgradientcolor='#274f95' canvasborderthickness ='0' canvasbordercolor = '#ffffff' numberprefix='' formatnumberscale='0' exportenabled='1' exportaction='save' exportatclient='0'>";      $colone .= "<set label='" . $readmit_values['label'] . "' value='" .$readmit_values['value']. "' color='#274f95' />";         $close_vals ="</chart>";         $xml_file_content = $open_vals.$colone.$close_vals;         $pick_time = time();         $file_name = 'dashboard_'.$pick_time;         $store_path = '/dashboard'.'/'.$file_name.'.xml';          write_file($store_path, $xml_file_content);