Hi Shoaib,
I'm afraid this cannot be done in CRM, its not an standard functionality, thinking on possible workarounds I cannot get nothing easy to do, maybe you can create some custom entity were you can store the detected duplicates and then to an export, but of course this means that your database is going to grow.
If this is only for a certain entity, you can maybe export all records to an excel and create some kind of function to detect duplicates in it.
Regards.