Near-infrared quantum cutting in Pr3+/Yb3+NaYF4 nanocrystals for luminescent solar converter

Pr3+ and Yb3+ co-doped NaYF4 nanocrystals (NCs) were synthetized via a simple coprecipitation method and investigated their efficiency of near-infrared quantum cutting (down-converter) with possible application for photovoltaic solar cells. The effect of the Yb3+ concentration on the down-conversion and quantum cutting emissions was evaluated under ultraviolet/visible excitation. The Pr3+ emissions under excitation at 442 nm were observed in the range from 450 to 1550 nm. It was obtained that increasing the Yb3+ concentration all the Pr3+ emissions decrease, and it was associated to an efficient energy transfer process between Pr3+ and Yb3+ ions. In addition, the Yb3+ emission at 974 nm decreases with the Yb3+ concentration increasing, being the highest emission observed for the NC doped with 2 mol.% of Yb3+. The lifetime of the P-3(0) state were measured and increasing the Yb3+ concentration the decay becomes faster leading to strong reduction of the lifetime from 18.6 (0 mol.% of Yb3+) to 2.2 mu s (10 mol%Yb3+). A quantum cutting efficiency of 188% in NaYF4 co-doped with 0.5 mol.% of Pr3+ and 10 mol.% of Yb3+ was obtained, which is a relatively high value, close to the limit of 200%. Therefore, these investigated NCs, synthetized via a very simple and cheap coprecipitation route, have great potential for solar cells applications of silicon-based materials by down-converting the ultraviolet/visible part of the solar spectrum to similar to 1000 nm photons.