PHP DateTime class not found

Hi,

Error
Class 'App\Controller\DateTime' not found

PHP Code:

$start = new DateTime($this->request->getPost('start_date'));
$end = new DateTime($this->request->getPost('end_date'));
$end = $end->modify( '+1 day' );
$interval = new DateInterval('P1D'); 


Correct me if I'm wrong but isn't DateTime class is built-in PHP 7? But codeigniter 4 cannot find the class.

Thank you for helping..