Publications

Solar energy harvesting is largely limited by the spectral sensitivity of the employed photovoltaic solar cell, since typically the full potential of each photon of the whole solar spectrum is not efficiently used in the generation of electricity. Therefore, increasing the overall solar spectrum utilization is of crucial interest and stands up as a frontier-of-research approach in the photovoltaic sector. Here we present an innovative ultra-broadband absorption and multiple spectral conversion approach, by means of rare-earth doped materials together with organic dyes embedded in a luminescent solar concentrator. The combination of different luminescent materials is a key factor for improving energy harvesting over the whole solar spectrum. At the same time, a simultaneously combined effect of up-conversion and down-shifting of light is aimed to optimal spectral matching with amorphous silicon solar cells response. Thus, UV–visible photons coming from the incoming sunlight, together with UV–visible up-converted photons coming from near-infrared radiation, can be all shifted to the yellow-orange-red part of the spectrum. To the best of our knowledge, this represents the first reported proof-of-concept using LSCs with up-conversion and down-shifting photonic processes working together and sequentially.

Anti-counterfeiting strategies are competitively developed against fast-growing counterfeit markets as a cornerstone for the next generation of luminescent security inks, so it will be more difficult to mimic by ever increasing sophisticated counterfeiters. In particular, rare-earth doped up-conversion luminescent materials present important advantages such as invisibility in ambient light, excitation by low cost NIR irradiation, lack in background noise and negligible auto-fluorescence from the surface. Here we present colour tuneable up-conversion emissions in two families of rare-earth doped photonic materials (sol-gel derived nano-glass-ceramics and glasses prepared by melt quenching technique) for tailoring the overall emitted luminescence, as a sort of “lightkey”. In particular, intensity ratios among UV and VIS up-conversion emission bands can be tuned by modifying doping concentration level and excitation power density, as an additional security feature itself, giving rise to a multi-digit security code based on light-responsive encrypted patterns. 

The present work aims to characterize the ephemeral mineral assemblage related to the fumarolic fields of the Tajogaite volcano, formed in 2021 in La Palma Island (Canary Islands, Spain). A set of 73 samples was obtained after two sampling campaigns in different fumarole sectors of the studied area. Mineralization related to these fumaroles formed efflorescent patches located at variable distance from the main volcanic craters. Distal patches are predominantly whitish, while in the vicinities they typically show yellowish to orange colours. Field observations also revealed that fumaroles usually occur in elevated topographic areas as well as over fractured and porous volcanic pyroclastic materials. The mineralogical and textural characterisation of the Tajogaite fumaroles unfolds a complex mineral assemblage, comprising cryptocrystalline phases related to low (< 200 °C) and medium temperature (200–400 °C) conditions. In Tajogaite, we propose a classification of three different fumarolic mineralization types: (1) fluorides and chlorides located in proximal fumarolic areas (~ 300–180 °C); (2) native sulphur associated with gypsum, mascagnite and salammoniac (~ 120–100 °C) and (3) sulphates and alkaline carbonates typically occurred in distal fumarolic areas (< 100 °C). Finally, we present a schematic model of the formation of Tajogaite fumarolic mineralization and their compositional evolution developed during the cooling of the volcanic system.

We are pleased to have this Special Issue of Optical Materials published following the successful SHIFT 2022 Conference “Spectral sHapIng For biomedical and energy applicaTions” held in Tenerife, Canary Islands (Spain) on October 10–14, 2022. The organizers: Universidad de La Laguna (Tenerife, Spain), with the financial support of the Canary Islands Government “Gobierno de Canarias”, Canary Islands Special low tax Zone (ZEC), City Hall of La Laguna “Ayuntamiento de La Laguna” and “Cabildo de Tenerife”, acknowledge all participants and authors for their valuable contributions to this Special Issue, entitled “Shift: shining a light on biomedical and energy applications”.Here, we present a collection of papers submitted to this Special Issue by some of the colleagues attending SHIFT2022 covering a wide gamut of fields from perovskite solar cells, luminescent solar concentrators, light guides, 3D-printing, photocatalysis, contrast agents for cell imaging among others. We are very much looking forward to shift again in the next edition SHIFT2025 (6–10 October 2025), Tenerife, Spain.

Gran Canaria is a hotspot-derived, intraplate, oceanic island, comprising a variety of alkaline felsic magmatic rocks (i.e. phonolites, trachytes, rhyolites and syenites). These rocks are enriched in rare-earth elements (REE) in relation to the mean concentration in the Earth's crust and they are subsequently mobilised and redistributed in the soil profile. From a set of 57 samples of felsic rocks and 12 samples from three paleosol profiles, we assess the concentration and mobility of REE. In the saprolite that developed over the rhyolites, we identified REE-bearing minerals such as primary monazite-(Ce), as well as secondary phases associated with the edaphic weathering, such as rhabdophane-(Ce) and LREE oxides. The averaged concentration of REE in the alkaline bedrock varies from trachytes (449 mg kg−1), to rhyolites (588 mg kg−1) and to phonolites (1036 mg kg−1). REE are slightly enriched in saprolites developed on trachyte (498 mg kg−1), rhyolite (601 mg kg−1) and phonolite (1171 mg kg−1) bedrocks. However, B-horizons of paleosols from trachytes and phonolites showed REE depletion (436 and 994 mg kg−1, respectively), whereas a marked enrichment was found in soils developed on rhyolites (1584 mg kg−1). According to our results, REE resources on Gran Canaria are significant, especially in Miocene alkaline felsic magmatic rocks (declining stage) and their associated paleosols. We estimate a total material volume of approximately 1000 km3 with REE concentrations of 672 ± 296 mg kg−1, yttrium contents of 57 ± 30 mg kg−1, and light and heavy REE ratios (LREE/HREE) of 17 ± 6. This mineralisation can be considered as bulk tonnage and low-grade ore REE deposits but it remains necessary to develop detailed mineral exploration on selected insular zones in the future, without undermining environmental and socioeconomic interests.