Solar spectral conversion for improving the photosynthetic activity in algae reactors

Sustainable biomass production is expected to be one of the major supporting pillars for future energy supply, as well as for renewable material provision. Algal beds represent an exciting resource for biomass/biofuel, fine chemicals and CO2 storage. Similar to other solar energy harvesting techniques, the efficiency of algal photosynthesis depends on the spectral overlap between solar irradiation and chloroplast absorption. Here we demonstrate that spectral conversion can be employed to significantly improve biomass growth and oxygen production rate in closed-cycle algae reactors. For this purpose, we adapt a photoluminescent phosphor of the type Ca 0.59Sr0.40Eu0.01S, which enables efficient conversion of the green part of the incoming spectrum into red light to better match the Qy peak of chlorophyll b. Integration of a Ca 0.59Sr0.40Eu0.01S backlight converter into a flat panel algae reactor filled with Haematococcus pluvialis as a model species results in significantly increased photosynthetic activity and algae reproduction rate

Luminescence of Ce3+ multicenters in Ca2+ -Mg2+ -Si4+ based garnet phosphors

Comparison of the luminescent properties of Ca3Sc2Si3O12: Ce and Ca2YMgScSi3O12: Ce single crystalline films (SCF) phosphors, grown by the liquid phase epitaxy method, was performed in this work. We have observed formation of the Ce3+ multicenters in Ca3Sc2Si3O12: Ce and Ca2YMgScSi3O12: Ce in the emission and excitation spectra as well as in the decay kinetics of the Ce3+ luminescence in SCFs of these garnets. Such Ce3+ multicenters possess different crystal field strength due to the inhomogeneous local surroundings of the dodecahedral positions of garnet host at the substitution of the octahedral positions by hetero-valence Mg2+ and Sc3+ ions and the tetrahedral positions by Si4+ ions. We confirm the presence of an effective energy transfer between different Ce3+ multicenters in Ce3+ doped Ca3Sc2Si3O12 and Ca2YMgScSi3O12 garnets. The positive trends in variations of the spectroscopic properties of the Ca2YMgScSi3O12: Ce garnet with respect to Ca3Sc2Si3O12: Ce garnet were observed also due to substitution of the dodecahedral sites of the garnet host by Y3+ ions and the octahedral sites by Mg2+ ions, which can be suitable for the development of new converters of white LEDs. Namely, due to the Y3+-Mg2+ doping, the luminescence spectrum of Ce3+ ions in Ca2YMgScSi3O12: Ce SCFs significantly extends in the red range in comparison with the Ca3Sc2Si3O12: Ce SCF counterpart

Luminescent and scintillation properties of Ce3+ doped Ca2RMgScSi3O12 (R = Y, Lu) single crystalline films

The work is dedicated to the growth and investigation of the luminescent and scintillation properties of single crystalline films (SCFs) of Ca2-xR1+xMg1+xSc1-xSi3O12:Ce (R = Y, Lu) mixed garnets with x = 0-0.25, grown using the liquid phase epitaxy method onto Y3Al5O12 substrates from PbO-B2O3 based flux. The absorption, luminescent and scintillation properties of Ca2-xY1+xMg1+xSc1-xSi3O12:Ce and Ca2-xLu1+xMg1+xSc1-xSi3O12:Ce SCFs with x = 0 and 0.25 were investigated and compared with the reference YAG:Ce and LuAG:Ce SCFs. Using the Ca2+, Mg2+ and Si4+ alloying, the Ce3+ emission spectra in Ca2-xR1+xMg1+xSc1-xSi3O12:Ce (R = Y, Lu; x = 0-0.25) SCFs can be notably extended in the red range in comparison with YAG: Ce and LuAG: Ce SCFs due to the increase of crystal field strength and Ce3+ multicenter creation in the dodecahedral positions of the lattices of these mixed garnet compounds. Due to the formation of Ce4+ ions, the as-grown Ca2-xR1+xMg1+xSc1-xSi3O12:Ce (R = Y, Lu) SCFs at x = 0 and 0.25 show relatively low light yield. However, after annealing in reducing atmosphere (95% N-2 + 5% H-2) at T > 1000 degrees C, a recharging Ce4+ -> Ce3+ takes place. After that, these SCFs possess the light yield about of 30% and 31% in comparison with the reference YAG: Ce and LuAG: Ce SCFs, respectively, and a fast scintillation response with the decay times in the ns range under a-particles excitation by Pu-239 (5.15 MeV) source

Industrially scalable and cost-effective Mn2+ doped ZnxCd1−xS/ZnS nanocrystals with 70% photoluminescence quantum yield, as efficient down-shifting materials in photovoltaics

We present colloidally stable and highly luminescent ZnxCd1−xS:Mn/ZnS core–shell nanocrystals (NCs) synthesized via a simple non-injection one-pot, two-step synthetic route, which can be easily upscaled. A systematic variation of the reaction component, parameters and thickness of the ZnS shell yielded doped nanocrystals with a very high photoluminescence quantum yield (Φpl) of 70%, which is the highest value yet reported for these Mn-doped sulfide-semiconductor NCs. These materials can be synthesized with high reproducibility in large quantities of the same high quality, i.e., the same Φpl using accordingly optimized reaction conditions. The application of these zero-reabsorption high quality NCs in the light conversion layers, deposited on top of a commercial monocrystalline silicon (mono-Si) solar cell, led to a significant enhancement of the external quantum efficiency (EQE) of this device in the ultraviolet spectral region between 300 and 400 nm up to ca. 12%. EQE enhancement is reflected by an increase in the power conversion efficiency (PCE) by nearly 0.5 percentage points and approached the theoretical limit (0.6%) expected from down-shifting for this Si solar cell. The resulting PCE may result in a BoM (bill of materials) cost reduction of app. 3% for mono-Si photovoltaic modules. Such small but distinct improvements are expected to pave the road for an industrial application of doped semiconductor NCs as cost-effective light converters for silicon photovoltaic (PV) and other optoelectronic applications

Application of scintillators based on single-crystalline Lu₃Al₅O₁₂:Ce³⁺ films for radiation monitoring in biology and medicine

Possibility of producing screens of X-ray detectors using liquid phase epitaxy on Y₃Al₅O₁₂ substrates covered by Lu₃Al₅O₁₂:Ce single crystalline films (SCF) is studied. Optical, luminescent and luminous characteristics of these SCF doped with isoelectronic La, Y, Sc impurities are analyzed. The possibility of crystallization of Lu₃Al₅O₁₂: Ce SCF on Y₃Al₅O₁₂ substrates by means of matching the lattice parameters of these garnets, when Lu³⁺ ions in Al³⁺ octa-sites, is proved. With the aim of matching the emission spectra of SCF based on Lu₃Al₅O₁₂: Ce, with the spectral sensitivity range of radiation detectors – CCD cameras – we investigated SCF containing Gd³⁺, Tb³⁺, and Eu³⁺ impurities. The maximum light yield, exceeding that of analogs based on Y₃Al₅O₁₂:Ce SCF by the factor of 1.1-1.5, is shown to be intrinsic for Lu₃Al₅O₁₂:Ce³⁺, Lu₃Al₅O₁₂:Ce, Y, La and Lu₃Al₅O₁₂:Ce, Tb SCF. An increase of the effective atomic number Zeff and density r up to the values of 60.6 and 7.35 g/cm³ respectively, enables the efficiency of X-ray absorption in comparison with Y₃Al₅O₁₂:Ce³⁺ SCF by the factor of 2.5–8 higher and to reach spatial resolution not less than 0.75–1.0 µm at the SCF thickness of 1.0–2.0 mm

Luminescence of F+F^+ and F centers in Al2O3−Y2O3Al_2O_3-Y_2O_3 oxide compounds

We summarize the results of investigation of spectral-kinetic characteristics of the luminescence of F+ and F-centers in Al2O3, YAlO3 (YAP) and Y3Al5O12 (YAG) crystals under excitation by synchrotron radiation in the transmittance and fundamental absorption ranges of these oxides. We show that the luminescence of F+ and F centers in the mentioned crystals can be excited via the corresponding intrinsic 1A?2A, 2B and 3P (F+) and 1S?3P, 1P (F) transitions of these centers, as well as via the radiative relaxation of excitons localized around F+ and F centers. In YAG crystal fast (2.3 ns) emission in the 400 nm band, excited at 3.33, 5.37 and 6.56 eV, arises from the F+-type centers, localized around YAl antisite defects (ADs). In Al2O3 and YAP crystals, the luminescence of excitons localized around F+ centers (LE(F+) centers) is revealed and the energies of formation of such excitons are determined as well. In YAG crystal the observation of the luminescence of LE(F+) centers is obscured due to presence of the large content (~0.2 at.%) of YAl ADs and formation of an excitons localized around YAl ADs and dimer F+-ADs centers

Luminescent properties of Ce3+\mathrm{Ce^{3+}} doped LiLuP4O12\mathrm{LiLuP_4O_{12}} tetraphosphate under synchrotron radiation excitation

The work is dedicated to the investigation of the luminescent and scintillation properties of the LiLuP$_4$O$_{12}$:Ce tetraphosphate, as a new scintillation material. The LiLuP$_4$O$_{12}$:Ce polycrystalline samples were grown by the Micropulling down (MPD) method. Under e-beam excitation and excitation with energy above the band gap of host, the LiLuP$_4$O$_{12}$:Ce crystals possess very strong Ce$^{3+}$ luminescence in the UV range in the bands peaked at 334 and 355 nm with a lifetime of 23 ns at room temperature. We have found that the scintillation light yield (LY) of polished plates prepared from MPD grown LiLuP$_4$O$_{12}$:Ce samples is relatively high and comparable with the LY of reference BGO crystal. Future improvement of the scintillation LY is expected at the optimization of the growth conditions of this compound. The energy structure of Ce$^{3+}$ ions, related to the 4f-5d transitions of Ce$^{3+}$ ions in the 3.7–25 eV range, was determined from the excitation and emission spectra of LiLuP$_4$O$_{12}$:Ce crystal under excitation by synchrotron radiation. We have also determined the energy of creation of excitons bound with Ce$^{3+}$ ions and estimated the energy gap in LiLuP$_4$O$_{12}$ host, which is equal to 8.5 and > 9.0 eV, respectively