Cooperative downconversion of Er3+/Yb3+ co-doped α-NaYF4 single crystals

The emission spectra from 500 nm to 1150 nm and decay curves at 542 nm under 487 nm excitation were tested for Er3+/Yb3+ co-doped α-NaYF4 single crystals grown with an improved Bridgman method. Cooperative downconversion (DC) with emission of two near-infrared photons about 1000 nm for each blue photon absorbed was observed in Yb3+ and Er3+ co-doped α-NaYF4 single crystals. The energy transfer process and quantum cutting mechanisms were presented through the analysis of the spectra. When the Er3+ concentration is fixed at about 0.4 mol%, the optimal concentration for ∼1000 nm emission is 9.98 mol% Yb3+ in the current research. The emission spectra dependence of the excited wavelength was also studied by exciting the samples with 379, 450 and 487 nm lights. The maximum quantum cutting efficiency approaches to 164.6% in α-NaYF4 single crystal of 0.42 mol% Er3+ and 9.98 mol% Yb3+.