Abstract: A method of measuring temperature includes positioning an optical fiber in contact with an object or in an environment having a temperature to be determined, where the optical fiber comprises a core surrounded by a cladding; the core comprises an alkaline-earth fluorosilicate glass including defects, and the cladding comprises a silica glass. Infrared light is supplied to the optical fiber, thereby electronically exciting the defects. Green light emitted from the defects is detected, and an intensity value of the green light is obtained and converted to a temperature value for the optical fiber, whereby the temperature of the object or environment is determined. The green light may be detected along a length of the optical fiber, and a plurality of intensity values may be converted to a plurality of temperature values along the fiber length, thereby obtaining a distributed measurement of the temperature of the object or environment.