Unable to change date format in Excel using PHP - php

Question

I am writing lots(around 900 rows) of data into a .xls file using class.writeexcel_worksheet.inc.php PHP class. All data written into excel is treated as simple text, even date and time stamps.
Now the problem is while filtering for dates in excel, there is no filter on for months or year. Since all cell values are simple text. Is there any way to format my cell to date data type while creating excel through PHP code?
CODE:
<?php
require_once "class.writeexcel_workbookbig.inc.php";
require_once "class.writeexcel_worksheet.inc.php";
require_once "db_params.php";
if(isset($_POST['submit']))
{
$heure = date("H_i");
$fname = tempnam("/tmp", $date."_".$heure.".xls");
$workbook = &new writeexcel_workbookbig($fname);
$worksheet = &$workbook->addworksheet();
$mainheading =& $workbook->addformat();
$mainheading->set_color('white');
$mainheading->set_pattern(0x1);
$mainheading->set_align('center');
$mainheading->set_border_color('black');
$mainheading->set_border(1);
$mainheading->set_merge();
$worksheet->write("A1", "Observation", $mainheading, $border2);
$worksheet->set_column(0, 50, 18);
$worksheet->freeze_panes(2, 0); # 1 row
$worksheet->merge_cells("A1:L1");
$heading =& $workbook->addformat();
$heading->set_color('white');
$heading->set_align('center');
$heading->set_align('vcenter');
$worksheet->set_column(0, 50, 18);
//$worksheet->set_outline();
$worksheet->set_margins(2);
# Create a border format
$border1 =& $workbook->addformat();
$border1->set_color('black');
$border1->set_pattern(0x1);
$border1->set_fg_color('white');
$border1->set_border_color('black');
$border1->set_border(1);
$border1->set_text_wrap();
$col=0;
$query = "SELECT * from Incidents";
$res=sqlsrv_query($conn,$query,array(), array('Scrollable'=>SQLSRV_CURSOR_STATIC));
$Entete1 = array("Incident ID - Hyperlink to AR" , "Reported Date", "Service", "Priority", "Operational Categorization Tier 1", "Summary", "Assignment Date", "Status", "Last Assigned Group", "Resolution Status", "Time bef. first assignment", "Number of assignments");
foreach($Entete1 as $value) {
$worksheet->write(1, $col, $value,$heading);
$col++;
}
$col=0;
$Entete11 = array("IncidentID", "ReportDate", "Service", "Priority", "OperationalCategoryT1", "Summary", "AssignmentDate", "Status", "LastAssignedGroup", "ResolutionStatus", "AcknowledgmentTime", "NoOFAssignment", "Team", "Remarks", "RemarkCategory" , "PloneforgeNo" ,"ProdCategorisationT1", "ProdCategorisationT2", "ProdCategorisationT3", "Urgency", "Impact", "Resolved_date", "Category_tier1", "ResolutionDetails", "Name", "LastResolvedDate", "Resolution", "OLAStatus", "OLAUpTime", "ReopenedDate", "StatusReason", "BucketDate", "OLAProgress", "DueDateTime", "GoalTime");
foreach($Entete11 as $value)
{
$x=2;
$y=2;
for( $position = SQLSRV_SCROLL_FIRST ; ($row=sqlsrv_fetch_array($res, SQLSRV_FETCH_BOTH, $position)) ; $position = SQLSRV_SCROLL_NEXT )
{
$chaine = strip_tags($row[$value]);
$worksheet->write($x, $col, $chaine, $border1);
$x++;
}
$col++;
}
$workbook->close();
header("Content-Type: application/x-msexcel; name=".$date."_".$heure.".xls");
header("Content-Disposition: inline; filename=".$date."_".$heure.".xls");
$fh=fopen($fname, "rb");
fpassthru($fh);
unlink($fname);
}
?>