Hi,
At this time it is hard to get some special IR photos in Ljubljana. It is not likely that you will see some sun, weather forecast is mostly cloudy, besides most of the time it Ljubljana has plenty of fog during winter. And no green grass or trees.
On the other hand there are a lot of chances to take lovely black and white photos.
Ljubljana is very safe, in last 20 years it became beautiful city (a bigger town to be honest

), there are many places where you can take great photos. My advice would be to visit a book store and take a look at some photo monography of Ljubljana so yo'll get the basic idea. You can ask then a sales person where are those places located. Ljubljana is small enough to get everywhere by foot and people mostly know the city pretty well.
For the start you can visit Tivoli park, castle, old town, Three bridges (and all other bridges over Ljubljanica river), market place, Cankarjev dom (cultural place, there are also two photo exhibitions at the moment, free entrance), Krizanke,...
Enjoy

Janez