Spectral variations and energy transfer processes on both Er³⁺ ion concentration and excitation densities in Yb³⁺-Er³⁺ codoped LaF₃ materials

In comparison with the up-conversion spectra of Yb³⁺-Er³⁺ codopded systems reported previously, the interesting intensity changes of up-conversion luminescence between the violet, the blue, the green and the red on the both Er³⁺ ion concentration and excitation density with 978 nm laser diodes as an excitation source were observed in Yb³⁺-Er³⁺ codopded LaF₃ powders. In order to clarify the change mechanisms, the up-conversion spectra of LaF₃: 10 mol% Yb³⁺, 0.5 mol% Er³⁺ and LaF₃: 10 mol% Yb³⁺, 1 mol% Er³⁺ were investigated and the results indicated that the cross-relaxation processes between Er³⁺ ions and the thermal population of the ²H_11/2 level play significant roles.