Excel Export Error

$model = new User;
			$res = $model->findAll();
			$data[]=array('Name','Email');
			
			foreach($res as $list) 
			{
				$data[]=array($list['username'],$list['email']);
						
			}
			Yii::import('application.extensions.phpexcel.JPhpExcel'); 
                $xls = new JPhpExcel('UTF-8', false, 'test'); 
                $xls->addArray($data); 
                $xls->generateXML('News-letter'.date('Y-m-d'));

I am using the above code to generate excel,
Excel is downloding fine, When I opens it it shows that error , file is in different format specified in the file name,

Can any one help me?