“…The stimulated-emission cross-sections were calculated by the Füchtbauer-Ladenburg (F-L) formula [44], [45],
where A q is the spontaneous emission probability for q polarization, I q ( λ ) is the fluorescence intensity as a function of wavelength. The peak emission cross-sections are about 0.81×10 −20 , 1.23×10 −20 and 0.84×10 −20 cm 2 for E||X , E||Y and E||Z respectively, which are comparable to other co-doped crystals, such as 1.89×10 −20 cm 2 for Er 3+ /Yb 3+ : KY(WO 4 ) 2
[46], 0.71×10 −20 cm 2 for Er 3+ /Yb 3+ : LaPO 4
[47] and 0.95×10 −20 cm 2 for Ce 3+ /Er 3+ NaLa(MoO 4 ) 2
[48].…”