Upconversion luminescence of Er3+ in chloride glasses based on ZnCl2 or CdCl2

Upconversion luminescence of Er3+ in the chloride glass system has been investigated in ZnCl2-BaCl2-KCl-ErCl3 and CdCl2-BaCl2-KCl-ErCl3 glasses. Under 800 nm excitation, the glasses gave upconversion luminescence with barely detectable red (around 660 nm), very intense green (around 525–560 nm), and considerably intense blue (around 410 nm) emissions. The intensity of blue emissions was far stronger than that observed for any of other Er3+-doped glass systems, revealing that Er3+-doped chloride glasses can efficiently convert the infrared light into much shorter wavelengths. The green emission is attributed not only to the thermally coupled 2H11/2 and 4S3/2→4I15/2 transition but also to the 2H9/2→4I13/2 transition. The blue emission is due to the 2H9/2→4I15/2 transition. The blue and green upconversion luminescence results from a two-photon process.