Lanthanide-based luminescent hybrid materials.

Interpretation of europium(III) spectra

Photovoltaic (PV) technologies for solar energy conversion represent promising routes to green and renewable energy generation. Despite relevant PV technologies being available for more than half a century, the production of solar energy remains costly, largely owing to low power conversion efficiencies of solar cells. The main difficulty in improving the efficiency of PV energy conversion lies in the spectral mismatch between the energy distribution of photons in the incident solar spectrum and the bandgap of a semiconductor material. In recent years, luminescent materials, which are capable of converting a broad spectrum of light into photons of a particular wavelength, have been synthesized and used to minimize the losses in the solar-cell-based energy conversion process. In this review, we will survey recent progress in the development of spectral converters, with a particular emphasis on lanthanide-based upconversion, quantum-cutting and down-shifting materials, for PV applications. In addition, we will also present technical challenges that arise in developing cost-effective high-performance solar cells based on these luminescent materials.

Enhancing solar cell efficiency: the search for luminescent materials as spectral converters

Photochemical splitting of water for hydrogen production by photocatalysis: A review

Recent progress in quantum cutting phosphors

Towards broad range and highly efficient down-conversion of solar spectrum by Er3+–Yb3+ co-doped nano-structured glass-ceramics

Glass ceramics of composition 95SiO2-5SnO2 doped with 0.4mol% Eu3+ have been prepared by thermal treatment of sol-gel glasses. The segregated SnO2 nanocrystals present a mean size comparable to the bulk exciton Bohr radius (about 2.4nm), corresponding to a wide band-gap quantum-dot system in an insulator SiO2 glass. A fraction of the Eu3+ ions is incorporated to the SnO2 nanocrystals in the process. In these strong confinement conditions, the energy gap presents a high dependence on the nanocrystal size. Taking advantage of this effect, it has been possible to excite selectively the Eu3+ ions located in the SnO2 nanocrystals, by energy transfer from the host, obtaining emission spectra that depend on the nanocrystal size. The Eu3+ ions environment in small nanocrystals (radius under 2nm) are very distorted, meanwhile they are like crystalline for nanocrystals with a radius of some nanometers.

Nanocrystal-size selective spectroscopy in SnO2:Eu3+ semiconductor quantum dots

Optical properties of Yb3+–Tb3+ codoped silica sol-gel samples have been studied after the gel to glass transition. Different upconversion emissions have been observed under near infrared excitation at about 1 μm. The Tb3+ ions are excited by means of energy transfer processes from Yb3+ ions. The temporal evolution of the blue-green upconversion emissions coming from Tb3+ ions and their dependence on the excitation intensity at about 1 μm has been studied. The experimental results are in good agreement with a cooperative resonant energy transfer mechanism from Yb3+ ions. An efficient backtransfer process is observed from Tb3+ ions towards Yb3+ ions. The upconversion efficiency, which is limited by this backtransfer process, has been obtained and compared with other upconversion results in similar matrix.

Cooperative energy transfer in Yb3+–Tb3+ codoped silica sol-gel glasses

Nanostructured silica based ceramic samples of composition (100− x)SiO2–xSnO2, doped with 0.4 mol% of Eu3+ and with x from 1 to 10, have been developed after a thermal treatment of precursor sol–gel glasses. A structural analysis has been performed by x-ray diffraction and high resolution transmission electron microscopy. The mean radius of the obtained SnO2 nanocrystals, ranging from 2 to 5 nm, is comparable to the exciton Bohr radius, corresponding to wide bandgap semiconductor quantum dots in an insulator SiO2 glass. A spectroscopy study in terms of emission and excitation spectra has been carried out as a function of SnO2 concentration. Moreover, time-resolved fluorescence measurements have also been performed in order to discern the emission of ions in glassy and nanocrystalline environments. The nanocrystal sizes have been obtained and compared by using the Brus and Scherrer equations.

https://iopscience.iop.org/article/10.1088/0957-4484/16/5/031/pdf

A.C. Yanes

Papers

Towards broad range and highly efficient down-conversion of solar spectrum by Er3+–Yb3+ co-doped nano-structured glass-ceramics

Nanocrystal-size selective spectroscopy in SnO2:Eu3+ semiconductor quantum dots

Cooperative energy transfer in Yb3+–Tb3+ codoped silica sol-gel glasses

Luminescent properties of transparent nanostructured Eu3+ doped SnO2?SiO2 glass-ceramics prepared by the sol?gel method

Luminescence and structural characterization of transparent nanostructured Eu3+-doped LaF3–SiO2 glass–ceramics prepared by sol–gel method