Infrared-to-visible photon avalanche upconversion dynamics in Ho3+-doped fluorozirconate glasses at room temperature

Blue, green and red emissions have been generated at room temperature by upconversion processes under infrared laser excitation at 750 and 840 nm in fluorozirconate glasses doped with Ho3+ ions. The intense green emission, associated to the 5S2, 5F4 → 5I8 transitions, has been carefully analysed in order to elucidate the mechanisms involved in the energy conversion process. The temporal dynamics of the emission intensities, the extremely weak ground state absorptions, the strong excited state absorptions and the different cross-relaxation processes indicate that two different photon avalanche mechanisms are responsible of the 750 and 840 nm laser-induced upconversion processes in the Ho3+-doped fluorozirconate glass.