Quantum tripling in Tm3+ doped La2BaZnO5 phosphors for efficiency enhancement of small band gap solar cells

The emission of three infrared photons at 1700 nm by Tm3+ for each absorbed photon at 465 nm is reported as a function of the Tm3+ concentration in La2-2xTm2xBaZnO5 phosphors. It was observed that the intensity of the Tm3+ F-3(4)-> H-3(6) emission with respect to emissions from the (1)G(4) state after (1)G(4) excitation at 465 nm increases when the Tm3+ concentration is raised from x=0.001 to x=0.032. This increase is the accumulated effect of four different possibilities for cross-relaxation that can take place between neighboring Tm3+ ions, which explains the efficiency of the quantum tripling process. An optimum in the cross-relaxation efficiency was found for the La1.936Tm0.064BaZnO5 phosphor. At higher Tm3+ concentrations the F-3(4)-> H-3(6) emission decreases as a result of concentration quenching. Quantum tripling can be used in high power IR phosphor converted LEDs or to increase the efficiency of small band gap solar cells like germanium. (C) 2014 Elsevier B.V. All rights reserved.