It sounds like the files haven't been added to the MediaStore database yet. You can check this by checking the gallery app - if they don't show up there they aren't in the DB yet.
Simply creating them does not automatically add them to the database - scans happen at regular trigger points(such as on reboot or remount of the external storage) or you can manually request a rescan.
To request a scan of a particular file you can call:
sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.fromFile(newFile)));
More information here: How can I refresh MediaStore on Android?