Examples of a monolithic phosphor composite for measuring a parameter of an object are disclosed. The composite comprises a thermographic phosphor and a metal oxide material that are dried and calcinated at high temperatures to form a ceramic metal oxide phosphor composite. The ceramic metal oxide phosphor composite is used in an optical device for measuring the parameter of the measuring object. The device comprises a fiber optic probe with a light guide, a light source operatively coupled to the fiber optic probe to provide excitation light into the light guide, a monolithic ceramic metal oxide phosphor composite functionally coupled to a tip of the fiber optic probe, a sensor operatively coupled to the fiber optic probe to detect the emitted light and a processing unit functionally coupled to the sensor to process the emitted light. When the monolithic ceramic metal oxide phosphor composite is illuminated with the excitation light it emits light in a wavelength different from the excitation light and a change in emission intensity at a single wavelength or the change in intensity ratio of two or more wavelengths, a shift in emission wavelength peak or a decay time of the phosphor luminescence is a function of the measuring parameter.