Infrared-laser precipitation of Dy3+-Yb3+ codoped SrF2 nanocrystals in glass and upconversion luminescence

Oxyfluoride glass-ceramics containing SrF₂nanocrystals have been prepared by a CO₂ laser treatment on the glass prepared by high temperature melt quenching. The optimized scan speed and laser power produced nanocrystals with sizes of ~10 nm. Energy dispersive spectroscopy mapping analysis showed that Dy³⁺ and Yb³⁺ ions are highly populated inside the SrF₂ nanocrystals. We also report a substantially enhanced down-converted visible emission from the 4F9/2 state of Dy3+ ions, including some violet emissions from the higher energy states under 365 nm excitation in the glass-ceramics, as compared to the as-made glass. Moreover, 980 nm laser diode excitation produced strong green and red emissions from the ⁴I_15/2 state and blue and yellow emissions from the ⁴F_9/2 state. A model has been proposed to interpret the upconversion emissions through the multistep-excitation of Dy³⁺ ions and energy transfers from, efficient sensitizers, Yb³⁺ ions to Dy³⁺ ions.