Blue and green upconverted emission in fluoroindate glasses under 808 nm excitation

In this study, the upconversion (UC) luminescence of fluoroindate glasses (InF₃G) co-doped with Yb-Nd-Er (Tm) ions excited in the NIR-I biological window was analyzed. In the first system, UC emission of singly Er³⁺ doped InF₃G under 808 nm excitation occurred to be more efficient than those observed in InF₃G co-doped with Yb–Er and Yb-Nd-Er. The intensity of UC emission (InF₃G-Er) was 22 % higher than InF₃G-Yb-Er, and even more than two times higher than in the InF₃G-Yb-Nd-Er sample. The effective energy transfer (η) between Nd³⁺- Yb³⁺ (η = 45 %) and Yb³⁺-Er³⁺ (η = 68 %), was reflected in the emission observed in the NIR region mainly, ascribed to Yb³⁺:²F_5/2 → ²F_7/2 (978 and 999 nm) and Nd³⁺:⁴F_3/2 → ⁴I_9/2 (1053 nm) transitions. Meanwhile, the samples co-doped with Tm³⁺ exhibited a strong dependence on Yb-Nd-Tm co-doping. Samples without Yb and Nd did not exhibit any UC emission due to the absence of pumping channel. This contrasts with the downshifting NIR emission, which was at least two times higher than those exhibited in samples co-doped Yb-Nd-Er. These results suggest that Tm³⁺ plays a crucial role in populating the lower-lying exited levels of Yb and Nd, influencing the overall emission behavior.