Greetings!
I actually first became acquainted with "fin de siecle" as a phrase from watching "Antiques Roadshow"! (Then I checked Wikipedia, to nail it down. They have a good article on it.) But yes, it is a recognized name amongst historians for a specific time period. Note that "fin de siecle"
means "end of the century" so that term will always refer to the close of the century. My understanding of "turn of the century" has always been that we were turning into a new century, so at the end of 1899/beginning of 1900 it was the "turn of the 20th century." I think you'll find that's the case, once you start your research. Try doing internet searches on both phrases, in quotation marks, to get yourself started. Always look for bibliography or source information on websites, even ones that you know your instructor won't allow you to cite as a source (like Wiki, probably) because often their references section leads to sources that you can use.
I hope this helps clear it up a bit!
Thanks,
Sarah, EssayForum.com
Sarah, EssayForum.com