A temperature sensor based on direct decay time measurement has been shown to reach a temperature as high as 1,600 °C. In that work, a doped YAG phosphor was grown onto an undoped YAG fiber to form a monolithic structure for the probe, and a laser was used as the excitation source. Subsequently, other versions using LEDs as the excitation source were realized. These devices can measure temperature up to 1,000 °C, and are used in microwave and plasma processing applications.