Luminescence decay-based Y2O3:Er phosphor thermometry: Temperature sensitivity governed by multiphonon emission with an effective phonon energy transition

To shift the onset of thermal quenching by multiphonon emission to higher temperatures, thermographic phosphors for high-temperature applications are usually selected with a large energy gap between the radiatively emitting energy level and the next lowest energy level. An alternate approach is presented where Y2O3:Er, with a relatively small energy gap of 2795 cm(-1) between the S-4(3/2) emitting level and the F-4(9/2) level below it, provides effective temperature measurements from room temperature to 1200 degrees C. The smaller energy gap results in an expanded temperature measurement range because (1) it results in a lower temperature onset of thermal quenching by multiphonon emission and (2) the smaller number of phonons required to bridge the energy gap produces a weaker temperature-dependent increase in multiphonon emission rates with temperature. Utilizing the intense hypersensitive I-4(15/2) -> H-2(11/12) Er3+ excitation at 522 nm offsets the temperature precision reduction due to the decreased decay time temperature sensitivity. Two distinct temperature sensitivity ranges are observed due to a crossover in multiphonon emission relaxation from high to low effective phonon energies at about 950 degrees C. The implications of this transition from high to low effective phonon energies for selection of dopant hosts for high-temperature thermographic phosphor applications are discussed.