MECHANISMS OF UP-CONVERSION FLUORESCENCES IN ER3+, TM3+ CODOPED FLUOROZIRCOALUMINATE GLASSES

The upconversion of infrared radiation into green and red fluorescences has been investigated for Er3+ and Tm3+ codoped fluorozircoaluminate glasses under 790 nm excitation. Introduction of Tm3+ into Er3+ doped system preferentially quences the green upconversion fluorescence from the 4S3/2 level of Er3+ due to the efficient cross-relaxation of H-3(6) --> I-4(15/2)(Er):H-3(6) --> H-3(4)(Tm) which can significantly reduce the upconversion efficiency from the I-4(13/2) level to the emitting S-4(3/2) level. However, the Tm3+ behaves as a good sensitizer of the red upconversion fluorescence from the F-4(9/2) level of Er3+ which is mainly populated by the cross-relaxation of H-3(4) --> H-3(6) (Tm):I-4(11/2) --> F-4(9/2)(Er). The excitation energy stored in the I-4(11/2) level of Er3+ migrates through the glass with a diffusion-limited regime. Through this regime, only Er3+ ions which have diffused their energy into the vicinity of Tm3+ ions can transfer the energy to the H-3(5) level of Tm3+. At lower Er3+ concentrations(less than or equal to 3 mol%), this diffusion-limited energy energy transfer upconversion from the I-4(11/2) level to the F-4(9/2) level of Er3+.