Introduction and Purpose of Yttrium

Yttrium is almost always found combined with the lanthanides in rare earth minerals and is never found in nature as a free element.
The most important use of yttrium is in making phosphors, such as the red ones used in television set cathode ray tube (CRT) displays and in LEDs. It is also used in the production of electrodes, electrolytes, electronic filters, lasers and superconductors; various medical applications; and the tracing of various materials to enhance their properties. Yttrium has no known biological role, and exposure to yttrium compounds can cause lung disease in humans.
Although metallic yttrium is not widely used, several of its compounds are. Yttrium oxide (Y2O3) and yttrium orthovanadate (YVO4) are both combined with europium to produce the red phosphor used in color televisions. Garnets made from yttrium and iron (Y3Fe5O12) are used as microwave filters in microwave communications equipment. Garnets made from yttrium and aluminum (Y3Al5O12) are used in jewelry as simulated diamond.

from:Rare Metals