This SBIR project is aimed at developing a novel thermometry technology with upconverting phosphors for temperature measurement in NASA's high-enthalpy wind tunnels. Conventional thermographic phosphors require illumination by ultraviolet (UV) light and emit light at visible wavelengths. However, UV excitation is problematic in many large-scale facilities because it demands very expensive UV-quality windows and the UV light can be absorbed and scattered by gas species and particles in the flow path. Upconversion phosphors have been previously developed in our company and the temperature-sensing effect up to around 1000ºC with excellent sensitivity was demonstrated. A major part of this Phase I efforts will be directed towards applying these thermographic phosphors to a surface coating on a model and tested in a wind tunnel environment. The objective is to develop new surface coatings that are aerodynamically smooth, very durable, require near IR excitation and enable surface temperatures in the range of 300 K to 1500 K to be measured.