Avalanche upconversion in Tm3+-doped BIGaZYTZr glass

Intense blue fluorescence is observed in a Tm3+-doped BIGaZYTZr fluoride glass after single wavelength red or infrared CW pumping. Dynamics and power dependences of both1G4 and1D2 fluorescences under 648.7 nm excitation reveal a photon avalanche mechanism in the 3 mol% doped sample. Selective pulsed excitation indicate an almost purely radiative relaxation at low concentration in agreement with Judd-Ofelt calculations. At higher concentration, cross-relaxation energy transfer and excited state absorption mechanism compete to feed the1G4 and1D2 levels. The concentration, temperature and time dependences of these fluorescences are investigated.