In at least one embodiment, the invention is a temperature sensor having a temperature sensitive material positioned within a shell. The shell has a first section and a second section, which are attached together by a non-adhesive bond. The non-adhesive bond being an atomic bond, such as a diffusion bond. The temperature sensitive material is capable of emitting a radiation signal which varies in its magnitude and character as the material's temperature changes. The shell allows transmission of the radiation signal through the shell to an external processor. Analysis of the emitted radiation signal by the processor can provide a temperature measurement. The temperature sensitive material is a phosphorescent, such as a phosphor. The shell may be made of a material which can be diffusion bonded, such materials include a silicon comprising material, a glass, a plastic, a sapphire and a quartz. The diffusion bond seals the shell, thus preventing the temperature sensitive material from being exposed to the surrounding environment. The sensor can include a stem attached to the shell. The stem is capable of transmitting and receiving radiation signals to and from the sensor by either positioning an optical fiber adjacent the sensor or by containing one or more waveguides.