In the 13th century, the Mongols conquered Persia to become the ruling class. From the 13th through the 16th century, thier influence in both clothing and culture is very evident in Persian art.
Most images of Mongols are actually from Persian art.
Several others far more knowledgeable than I have done extensive research in this area. The following are links to some of this research.
Basic information on Mongol Dress
The Red Kaganate: Information on Mongol Clothing and Culture --this site has several extent garments as well as patterns and instructions
Making a Mongal Del --great research and pattern to make a Mongol Del (caftan)
LACMA Exhibition on Genghis Khan