An assembly, for example an electrostatic chuck, is provided including a substrate, an electrostatic chuck, a heating plate, and a bond layer comprising a phosphorescent material. In one form, an optical sensor is disposed proximate the bond layer to detect a temperature of the bond layer in the field of view of the optical sensor. The phosphorescent material is illuminated and the subsequent decay is observed by the optical sensor. From this information, the temperature of the electrostatic chuck and substrate is determined and heating elements may be adjusted by a controller.