Impact of Er³⁺ Concentration on Luminescence in NaLaF₄

In this work, NaLaF₄ doped with Er³⁺ of different concentrations was synthesized. The luminescence spectrum for NaLaF₄:Er³⁺ (0.2 mol%) at 489 nm excitation reveals characteristic Er³⁺ luminescence bands in the green (540 nm), red (660 nm) and infrared (980 nm) spectral regions. The green luminescence band originated from the ⁴S_3/2 → ⁴I_15/2 transition is the most intensive one in the luminescence spectrum. As the concentration of the activator is increasing, the intensity of all luminescence bands changes significantly. The super-linear increase of the infrared luminescence intensity with increasing Er³⁺ concentration as well as the quenching of green luminescence at the concentrations exceeding 2 mol% can be attributed to the cross-relaxation process between the activator ions.