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

Increased thermal stabilization of polymer photovoltaic cells with oligomeric PCBM

The first oligomerisation of phenyl-C61-butyric acid methyl ester (PCBM) using a facile atom transfer radical addition polymerization (ATRAP) and its exploitation for organic photovoltaic devices is described. Oligo{(phenyl-C61-butyric acid methyl ester)-alt-[1,4-bis(bromomethyl)-2,5-bis(octyloxy)benzene]} (OPCBMMB) shows opto-electronic properties equivalent to those of PCBM but has a higher glass transition temperature. When mixed with various band gap semiconducting polymers, OPCBMMB delivers performances similar to PCBM but with an enhanced stabilization of the bulk heterojunction in photovoltaic devices on plastic substrates under thermal stress, regardless of the degree of crystallinity of the polymer and without changing opto-electronic properties

Luminescent properties and energy transfer processes in YAG:Er single crystalline films

The paper is dedicated to studying the optical properties of YAG:Er single crystalline films (SCF) grown by liquid phase epitaxy. The absorption, cathodoluminescence and photoluminescence spectra were measured for the YAG:Er SCFs with different doping levels of Er3+ from 0.735 to 6.6 at%. The luminescence spectra and luminescence excitation spectra under synchrotron radiation excitation in the fundamental absorption range of the YAG and in the intrinsic f–d absorption bands of Er3+ ions reveal the peculiarities of energy transfer from the YAG host to the Er3+ ions

Effect of HPHT annealing on the photoluminescence of synthetic diamonds grown in the Fe-Ni-C system

The photoluminescence (PL) spectra of synthetic diamonds (SD) containing high concentrations of nitrogen and nickel impurities have been examined in both as-grown samples and the ones annealed at 1950 or 2200 K. A large number of zero-phonon lines (ZPLs), including two tens of vibronic PL systems, have been identified and their behaviour on annealing has been studied, one-third of documented lines have also been observed in natural diamonds. An analysis of their behaviour on annealing allows their division into three main groups, namely: (I) The systems present in as-grown SD, but which disappear after annealing at 1950 K; (II) The systems, which appear after annealing at approximately 1950 K, but their intensity is lower or they disappear completely after annealing at 2200 K; (III) The system, whose intensity increases after annealing at 1950 K and does not decrease after further annealing at 2200 K. A combined optical and ESR study allowed one to identify the systems of group I with individual impurities, whereas the items within group III were associated with nickel-nitrogen complexes containing a single nickel ion in the divacancy position surrounded by a few (n≥2) nitrogen atoms. The systems within group II are related to a relaxed single nickel defect (nickel ion in divacancy position) and simple nickel-nitrogen complexes, containing a single nitrogen atom. The PL excitation spectra were measured for 15 most intense PL systems. A broad absorption band in the annealed SD, with a peak approximately 450 nm and a superimposed fine structure, was decomposed into individual components, related to the NE1, NE2 and NE3 paramagnetic centres. The lower excited states of these three centres are split with Δ E=125 meV, 62 meV and 221 meV, respectively, while the spin-allowed electronic transitions take place only to the upper sublevel. © 2003 Elsevier Science B.V. All rights reserved

Synthesis and luminescent properties of prospective Ce3+ doped silicate garnet phosphors for white LED converters

The results on crystallization and investigation of the luminescent properties of prospective ceramic phosphors based on the Ce3+ doped {Ca2R}[ScB](CSi2)O12 (R = Lu, Y, Gd; B = Sc, Ga, C = Ga, Al) silicate garnets are presented for the first time in this work. We have observed the variations of the spectroscopic properties of Ce3+ ions in the mentioned Ca2+-Si4+ garnet hosts depending on the cation content at the dodecahedral {}, octahedral [] and tetrahedral () sites of garnet lattice. These results can be useful for the development of new generation of ceramic phosphor converters for white LEDs based on the garnet compounds under study