Absolute Upconversion Quantum Yield of ß-NaYF4 Doped with Er³+ and External Quantum Efficiency of Solar Cell Upconverter Devices under Broad-Band Excitation considering Spectral Mismatch Corrections

We investigate the upconversion quantum yield of v-NaYF4:Er3+ under broadband excitation both experimentally and theoretically. The upconversion quantum yield strongly depends on the erbium concentration, and shows a maximum for an erbium concentration of 25%.