THE COLOR OF MEDICAL-GRADE ZIRCONIA (Y-TZP)

Optical spectroscopy, ESR spectroscopy, and standard and wavelength- a nd-temperature-resolved thermoluminenscence spectroscopy of as-sintere d and gamma-irradiated medical-grade yttrium-stabilized tetragonal zir conia polycrystal (Y-TZP) material showed that the pronounced colour c hange, after irradiation, from off-white to a purplish-grey shade can be related to two electronic transitions at local defects in the cryst al lattice. The first transition could be associated with an electron- hole state characterized by an oxygen ion trapped in the vicinity of a yttrium ion (Y'O-Zr) and can be correlated with an optical absorptio n band at 2.6 eV (480 nm). The second transition is presumably an extr insic defect correlated with an optical absorption band at 3.2 eV (395 nm). From the experimental results it can be concluded that those loc al electronic defects responsible for the colour change on gamma-irrad iation do not influence safety-related mechanical or chemical properti es of the ceramic femoral ball heads of hip endoprostheses produced fr om Y-TZP.