Excited-State Upconversion of Pr(0.5)Yb(1.5):ZBLAN under Two-Colour Excitation

We report the excited-state upconversion in Pr(0.5)Yb(1.5):ZBLAN under two-colour excitation of 960nm laser and xenon lamp light. Three obvious upconversion excitation peaks around 856.0, 804.2 and 787.1nm were observed and the involved mechanism has been explained. The measured upconversion excitation peak 856.0nm corresponds to the sum of theoretical values 852nm and 866nm owing to the ¹G₄(Pr³⁺)→ ¹I₆(Pr³⁺) and ¹G₄(Pr³⁺)→ ³ P₁(Pr³⁺) excited state absorption transitions. The measured 804.2 and 787.1nm upconversion excitation peaks originate from the excited state absorption transitions ³⁺H₆(Pr³⁺)→ ¹D₂(Pr³⁺) and ¹G₄(Pr³⁺)→ ³⁺P₂(Pr³⁺), respectively. The excited state absorption upconversion ¹G₄(Pr³⁺)→ ¹I₆(Pr³⁺) is strong because of its large oscillator strength f=23.040×10^-6.