Making Eu<sup>2+</sup>- and Sm<sup>2+</sup>-Doped Borates Fit for Solar Energy Applications
L.J.B. Erasmus, Philippe F. Smet, R.E. Kroon, Dirk Poelman, J.J. Terblans, Jonas Joos, David Van der Heggen, H.C. Swart
Abstract
Despite the development of many luminescent materials for various applications, only a few of these phosphors are applicable for solar energy generation applications. This study used the conventional solid-state reaction method to synthesize different strontium borate compounds codoped with divalent europium and samarium ions. The material was optimized by varying the experimental procedure, the molar ratio of the boron, and the molar ratios of both codopants. Strontium hexaborate doped with a relatively high europium concentration and a low samarium concentration (Sr 0.89 B 6 O 10:Eu 0.1, Sm 0.01 ) gave the optimum optical properties. These properties included a broad excitation range from 220 to 600 nm containing contributions from divalent europium and samarium ions. The material exhibited strong and narrow emission in the region from 650 to 850 nm following radiative transitions within the divalent samarium ions. The internal luminescence quantum efficiency of the optimized material was 79% (λ ex = 508.5 nm). There was no spectral overlap between the excitation and emission spectra, thereby reducing the reabsorption probability. These marked characteristics make this phosphor material appropriate for use as a solar radiation converter or for use in luminescent solar concentrators.