Source http://www.mwasif.com/2007/5/download-data-csv-using-php/

Solution worked for me

Danish Zahur said,

October 7, 2009 @ 7:23 pm

If your contents are in UTF-8 format, then no need to convert encoding. Just start your file/output stream with UTF-8 BOM after headers.

echo pack("CCC",0xef,0xbb,0xbf);

And header should contain encoding UTF-8

header( "Content-type: application/vnd.ms-excel; charset=UTF-8" );

It will work like charm because Excel will recognize file charset with BOM bytes.