Hi folks,
Can anyone give me information on differences between releases of DB2 LUW from 8.1.1 to 9.7 (iam only looking till 9.7)

Any links, materials where i can have the same? (I am able to get only complete information on each release, but not the differences.)

Thanks

If you look at the doc, each has a "What's New" guide (online or PDF).

Version 8.x is discontinued by IBM and no longer supported.

The basic difference is version 8 and version 9 and above..
DB2 v8 -- Not multithreaded engine
Db2 v9 and above --> multithreaded engine.

Diffenences:
1. The format of the application ID has changed to readable format.
2. Modification of Product identification strings was changed. The modification level portion of the product identifier can contain characters from A to Z.
3. Cursor blocking is disabled for SQL procedures. The data is always received one row at a time, regardless of the value that you specify for the BLOCKING bind option.

Like this there will be so many diffences. please refer info center links:
Version 9 incompatibilities with previous releases and changed behaviors
What's new in DB2 V9.5: Changed functionality
What's new in DB2 V9.7: Changed functionality

v9.5 and above --> multithreaded engine

This may be some interesting piece of information for a DBA, but an application programmer can't probably care less about this change. So the real question is what kind of changes the OP is interested in? Enhancements to the SQL functionality vs. internal changes vs. admin-related changes, etc. "What's new?" is the best starting point for that. Everything else is just an extremely condensed list of improvements that may/will miss important things.