Tailoring the 4I9/2→4I13/2 emission in Er3+ ions in different hosts media

The 4I9/2 -> 4I13/2 emission band of Er3+ is potentially interesting for CH4 detection because it can overlap with the optical absorption band of CH4. GaLaS and GeGaS glasses doped with Er3+ ions show the desirable emission under 808 nm excitation. An attempt of spectrally shifting 4I9/2 -> 4I13/2 emission band by substituting S by O or Se to obtain a perfect match to the absorption band of CH4 leads to the weakening and disappearance of the 4I9/2 -> 4I13/2 band. This phenomenon is tentatively related to the acceleration of non-radiative relaxation in the case of oxygen addition and to the suppression of up-conversion in the selenium substitution case. The relative intensity of the 4I9/2 -> 4I13/2 band (with respect to the 4I13/2 -> 4I15/2 band) varies significantly in powdered and bulk materials. This effect is discussed in terms of the radiation diffusion (i.e. radiation trapping) model and is confirmed by Monte-Carlo simulations.