Re-absorption process in the upconversion green emission of the erbium ion-doped fluorozirconate glass system

In this paper we report the upconversion emission for the ⁴S_3/2→⁴I_15/2 Stark components of Er³⁺ ion-doped fluorozirconate glass at T=2 K. The spectrum shows only seven peaks, one less than expected theoretically, being missing the peak at the wave number 17,996 cm⁻¹ (λ=555 nm). This result is compared with the luminescence for the same transition at the same conditions which exhibits the eight expected lines. Such a discrepancy is attributed to a re-absorption process (ESRA) between the energy levels ⁴I_13/2 and ²H_9/2.