Abstract
Silicon-aluminum-oxigen (SiAlO) coatings doped with Sm2+ and prepared by reactive magnetron co-sputtering of Si, Al, and Sm targets, are attractive for luminescence solar concentrator applications but suffer from the low absorption between 300 and 600 nm. This article reports that the main cause of low absorption is a high concentration of undesired Sm3+. This finding is supported by optical transmittance, photoluminescence emission and excitation characterization, and X-ray photoelectron spectroscopy data of the Sm's 3d5/2 edge. We present an alternative deposition process for obtaining Sm doped SiAlO layers with enhanced Sm2+ absorption by incorporating Sm through the use of multilayer thin-film precursors composed of metallic Sm and SiAlO layers. After thermal post-deposition treatments, diffusion and reaction of the metallic Sm layers with the SiAlO host results in coatings showing the characteristic 5d → 4f transitions of Sm2+ in the region between 250 and 600 nm which were not detectable in Sm-doped single layers. This same deposition strategy produces Tm doped SiAlO coatings with Tm2+‘s characteristic luminescence at 1132 nm when the SiAlO host is in the mullite composition region. The photoluminescence excitation spectrum of Tm2+ is compared to phosphor with similar composition and covers the range between 300 and 700 nm.
Highlights
Luminescent Solar Concentrators (LSCs) have strong potential to be part of future net-zero-energy buildings if applied as electricitygenerating windows [1]
To identify each sample while discriminating the synthesis method used for each we have opted for adding a prefix to the sample name: “SL” indicates the films grown using the conventional single-layered coatings by reactive magnetron cosputtering; “ML” indicates the films prepared by using multilayered thinfilm precursors (MTFP) - method described in this work; and “SG” the phosphors prepared by sol-gel sintering
As reported earlier [5], in thin-films prepared by reactive magnetron co-sputtering of the Al, Si, and Sm targets, the observed absorption in this spectral range was estimated to be only of the order of 1% despite considering thick (3–4 μm) heavily Sm-doped (2–8 at.%) samples
Summary
Luminescent Solar Concentrators (LSCs) have strong potential to be part of future net-zero-energy buildings if applied as electricitygenerating windows [1]. The 4f6 → 4f6 emission transitions of Sm2+ do not suffer from self-absorption due to inter-configurational and non-radiative relaxation via 4f55d1 → 4f6 transitions (see Fig. 1A) This results in a wider absorption range up to 600 nm in the visible spectrum. The absorption spectra showed absorp tion intensity of the order of 1%, or even lower at specific wavelengths, despite relatively thick (3–4 μm) and highly Sm-doped (2–8 at.%) films. It contrasts with the work on Eu2+ doped SiAlON thin films [6]. One hypothesis raised to explain the low Sm2+ absorption was that, when Sm was inserted in sputtered SiAlO coatings, metallic Sm or Sm2O3 nano-inclusion could be present. We show that the main cause for the reported low absorption of Sm2+ in Sm doped SiAlO (SiAlO:Sm), in contrast to Eu2+, is that Sm is present as Sm3+
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