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Transparent NaLuF4 glass-ceramics (GCs) doped with Tm3+ and Tm3+/Yb3+ have been prepared by melting-quenching followed by thermal treatment at temperatures near the glass transition temperature. The crystallization process has been studied using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). NaLuF4 nanocrystals (NCs) ranging 9–30 nm in size are the only crystalline phase, the crystal size increasing with the dopant concentration. Energy dispersive X-ray (EDX) measurements confirm the Tm3+ and Yb3+ incorporation in the NCs. Optical characterization included the analysis of up-conversion (UC) as well as the Near-infrared (NIR) luminescence. NIR emission spectra of Tm3+ and Yb3+ in co-doped samples confirmed an efficient energy transfer between both ions. No UC emissions are observed in Tm3+ single-doped glass and GCs. Yb3+ incorporation favors the Tm3+-Tm3+ UC processes resulting in Tm3+ blue, yellowish-red and NIR UC emissions after excitation at 975 nm. Blue UC emission is also observed in the codoped samples after Tm3+ excitation at 791 nm. These effects were more evident for the GCs compared to the base glasses, confirming the RE ions incorporation in the NCs. As a result, these GCs can be used to tune the UC emission from NIR to blue by selective excitation., This work was supported by MINECO under Projects MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE), Basque Country Government PIBA2018-24 and Basque Country University GIU17/014. This article is part of the dissemination activities of project FunGlass. This project has received funding from the European Union´s Horizon 2020 research and innovation programme under grant agreement No 739566. This article was also created in the frame of the project Centre for Functional and Surface Functionalized Glass (CEGLASS), ITMS code is 313011R453, operational program Research and innovation, co-funded from European Regional Development Fund. This research work has been supported by the Research Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic, by the project: Advancement and support of R&D for "Centre for diagnostics and quality testing of materials" in the domains of the RIS3 SK specialization, Acronym: CEDITEK II., ITMS2014+ code 313011W442.

Transparent oxyfluoride glass-ceramics (GCs) with embedded β-Na1.5Y1.5F6 crystals doped with Er3+ ions were fabricated by a melt-quenching method with subsequent heat-treatment. The structural characterizations and spectroscopic techniques were performed to verify the precipitation of β-Na1.5Y1.5F6 crystals and partition of the Er3+ dopant into the crystals. Bright green up-conversion (UC) emission was achieved in Er3+-doped glass-ceramic (Er-GC). Furthermore, the temperature-dependent visible UC behavior based on thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs) was also examined in the temperature range 298 k to 823 K with maximum relative sensitivity (Sr) of 1.1% K−1 at 298 K for TCLs in Er-G and Er-GC samples.

Transparent oxyfluoride glass&ndash, ceramics containing NaGdF4 nanocrystals were prepared by melt-quenching and doped with Er3+ (0.5 mol%) and different amounts of Yb3+ (0 mol%&ndash, 2 mol%). The selected dopant concentration the crystallization thermal treatments were chosen to obtain the most efficient visible up-conversion emissions, together with near infrared emissions. The crystal size increased with dopant content and treatment time. NaGdF4 NCs with a size ranging 9&ndash, 30 nm were obtained after heat treatments at Tg + 20&ndash, 80 &deg, C as confirmed by X-ray diffraction and high-resolution transmission electron microscopy. Energy dispersive X-ray analysis shows the incorporation of rare earth ions into the NaGdF4 nanocrystals. Near-infrared emission spectra, together with the up-conversion emissions were measured. The optical characterization of the glass&ndash, ceramics clearly shows that Er3+ and Yb3+ ions are incorporated in the crystalline phase. Moreover, visible up-conversion emissions could be tuned by controlling the nanocrystals size through appropriated heat treatment, making possible a correlation between structural and optical properties.

Transparent oxyfluoride glass-ceramics (GCs) were prepared starting from the glass composition 70SiO2–7Al2O3–16K2O–7LaF3 (mol%) doped with four different Nd3+ concentrations (0.1–2 mol%). The glass-ceramics were prepared by heat treatment above the corresponding glass transition temperatures (Tg + 10–100 °C). Depending on the Nd3+ concentration, cubic (α-phase) and hexagonal (β-phase) KLaF4 nanocrystals (NCs) precipitated from the starting glass. By X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM), the crystallization of the cubic structure was observed for all compositions, while β-KLaF4 nanocrystals were mostly detected for the glass-ceramic samples doped with 0.5 mol% NdF3. This noteworthy result is confirmed by site-selective laser spectroscopy. The presence of α-KLaF4 and β-KLaF4 crystalline phases is unambiguously identified from the emission and excitation spectra and lifetime measurements of the 4F3/2 state of Nd3+ ions. The spectroscopic results confirm those obtained with XRD and HR-TEM techniques: α-KLaF4 NCs are found to be present for all NdF3 concentrations whereas β-KLaF4 NCs are predominant in the glass-ceramic samples doped with 0.5 mol%., This work was supported by MINECO under projects MAT2013-48246-C2-1-P/-2-P and MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE) and Basque Country University PPG17/07 and GIU17/014. We acknowledge the European Syncrothron Radiation Facility for the provision of synchrotron radiation facilities in using the beamline BM25-SpLine to perform the experiments MA-3350 and 25-01-1014. Aluisio A. Cabral and Jose Joaquín Velázquez also acknowledge CAPES (#BEX 2598/15-9) and MINECO for Grant FPDI-2013-16895, respectively.

Novel transparent oxyfluoride nano-glass-ceramics containing undoped and 0.5 Eu (mol%) doped NaGdF nanocrystals (NCs), were obtained by sol-gel for the first time. X-ray diffraction (XRD) confirms the precipitation of α- and β-NaGdF NCs with a size ranging between 5 and 24 nm. When the Na:Gd ratio, temperature and heating time are fixed to 0.95:1, 550–600 °C and 1–8 h, respectively, only the β-NaGdF phase precipitates. These results are confirmed by high-resolution transmission electron microscopy (HRTEM). The decomposition of trifluoroacetic acid (TFA) and the formation of fluoride lattice bonds were studied by Fourier transform infrared spectroscopy (FTIR). Thus, the sol-gel route permits NaGdF glass-ceramics to be obtained through the control of Na:Gd ratio, temperature and heating time. The incorporation of dopant ions in the NaGdF NCs was confirmed by photoluminescence measurements which show narrow and well-resolved Eu emission and excitation spectra in GCs. Moreover, the low asymmetry ratio values between the electric dipole (D → F) to the magnetic dipole (D → F) transitions indicate that Eu ions are incorporated in the NaGdF NCs. Furthermore, efficient Gd→ Eu energy transfer results in an enhancement of the reddish Eu emissions, further supported by fluorescence decay lifetimes., This work was supported by MINECO under Projects N° MAT2013-48246-C2-1-P/2-P and MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE),and Basque Country University PPG17/07 and GIU17/014. This paperis a part of dissemination activities of the project FunGlass. This projecthas received funding from the European Union's Horizon 2020 researchand innovation programme under grant agreement No 739566

Trabajo presentado en SPIE OPTO, celebrado en San Francisco (Estados Unidos), del 2 al 7 de febrero 2019, Transparent oxyfluoride glass-ceramics obtained by the adequate heat treatment of Nd3+-doped glass with composition 70SiO2–7Al2O3–16K2O–7LaF3 (mol%) are investigated. Site-selective laser spectroscopy demonstrates that depending on the Nd3+ concentration, cubic (α-phase) and hexagonal (β-phase) KLaF4 nanocrystals precipitate from the starting glass. The presence of both crystalline phases are unambiguously identified from the emission and excitation spectra and lifetime measurements of the 4F3/2 state of Nd3+ ions. The spectroscopic results are in agreement with those obtained with XRD and HR-TEM techniques: α-KLaF4 nanocrystals are found to be present for all NdF3 concentrations whereas β-KLaF4 nanocrystals are predominant in the GC samples doped with 0.5 mol%.

[EN] Novel glass-ceramic optical fibers containing NaLuF nanocrystals doped with 0.5ErF and 2YbF (mol%) have been prepared by the rod-in-tube method and controlled crystallization. NaLuF nanocrystals with a size around 20 nm are obtained after heat treatment at 600 °C. Intense upconverted green and red emissions due to (H, S) → I and F → I transitions, respectively, together with a blue emission due to H → I transition have been observed under excitation at 980 nm. The intensity of the green and red upconversion bands shows a nearly linear dependence on the excitation power which can be explained by saturation effects in the intermediate energy states and proves that a sensitized energy transfer upconversion process is responsible for the population of the emitting levels of Er ions. The upconversion emission color changes from yellow to green by increasing the excitation power density which allows to manipulate the color output of the Er emission in the glass-ceramic fibers. The tunable emission color is easily detected with the naked eye. This interesting characteristic makes these glass-ceramic fibers promising materials for photonic applications., This work was supported by MINECO under the project MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE) and Basque Country University PPG17/07 and GIU17/014, and Basque Government PIBA2018-24. Funding from MPNS Cost Action MP1401 is also acknowledged. This paper is a part of dissemination activities of project FunGlass. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 739566.

We present research on Ca3Sc2Si3O12 garnets doped with Ce3+ and Er3+ ions that were synthesized by the freeze-drying precursor method. The structural characterization was performed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) images of the calcined material were studied. Nanocrystals of Ca3Sc2Si3O12 were obtained by calcining the precursor at 1200 degrees C for 4 h with a mean size of about 100 nm. The luminescence features of Ce3+ and Er3+ doped samples indicated that these ions are effectively incorporated into the crystalline phase. In addition, codoping with Ce3+-Er3+ ions results in energy transfer processes from Ce3+ to Er3+ ions which led to the enhancement of near-infrared luminescence at 1.5 mu m. The efficiency of this non-radiative energy transfer process has been studied by means of excited state dynamics as a function of the doping concentration. From these results we have found that near-infrared Er3+ luminescence efficiency under VIS Ce3+ excitation is at maximal for 1Ce(3+)-1Er(3+) codoped Ca3Sc2Si3O12 garnets (in mol%). Luminescence quenching at higher Er3+ ion concentrations is observed.

Transparent oxyfluoride nano-glass-ceramics (GCs) containing NaGdF4 nanocrystals doped with 0.1Pr3+and 0.5Pr3+, and co-doped with 0.5Pr3+-2Yb3+ ions (mol%) were obtained by melting-quenching followed by heat treatments at temperatures near Tg. The addition of rare-earths (RE) ions affects the crystallization kinetics due to the progressive increase of Tg as RE concentration increases. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) show the precipitation of NaGdF4 nanocrystals with sizes between 9 and 30 nm. The crystal size increases with the increasing amount of dopant. Energy dispersive X-ray (EDX) analysis confirms the incorporation of the RE ions in the fluoride nanocrystals in the glass-ceramics. This incorporation is also supported by optical characterization. Photoluminescence measurements shows a better resolved structure together with a narrowing of the Pr3+ emission and excitation spectra in the glass–ceramics compared to the precursor glass. The emission spectra and fluorescence decay curves from the 3P0 level of Pr3+ in the codoped samples support the existence of a Pr3+ → Yb3+ energy transfer with slight enhancement of the energy transfer efficiency in the GC sample., This work was supported by MINECO under Projects MAT2013-48246-C2-1-P and MAT2013-48246-C2-2-P and Basque Country UniversityPPG17/07. J.J. Velázquez also acknowledges MINECO under Grant FPDI-2013-16895. Gang Chen acknowledges the U.S. National Science Foundation for partial support under Grant #DMR-1507670.

Trabajo presentado al SPIE Photonic West: Optical Components and Materials XV, celebrado en San Francisco, California (USA) del 29 al 31 de enero de 2018., Transparent oxyfluoride glass-ceramics obtained by the adequate heat treatment of Nd3+-doped glass with composition SiO2-Al2O3-Na2O-LaF3 are investigated. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) show that the precipitated nanocrystals are LaF3 with a crystal size between 9-12 nm. Furthermore, energy dispersive X-ray (EDX) analysis shows the incorporation of Nd3+ ions into the LaF3 nanocrystals. Site-selective and time-resolved emission and excitation spectra of the 4F3/2 and 4F5/2 states, allows to unambiguously isolate the emission of Nd3+ ions in LaF3 nanocrystals which shows well defined spectra, similar to those obtained for pure LaF3 crystal., This work was supported by the Spanish Government MEC under Projects No. MAT2013-48246-C2-1-P, MAT2013-48246-C2-2-P, and MAT2017-87035-C2-2-P and the University of the Basque Country PPG17/07.

Transparent glass ceramic (GC) films and self-supported layers of composition 80SiO-20LaF doped with Nd were prepared by sol-gel method for the first time. GC films were deposited by dip coating on different substrates and heat-treated between 350°C and 850°C for 1, 3, and 80 hours. The structural analysis of thin films was performed by GI-XRD and HR-TEM to check the LaF nanocrystals precipitation in the SiO matrix, revealing a crystal size lower than 5 nm. The emission and excitation spectra and lifetimes of the films have been obtained for different thermal treatments and Nd contents. The luminescence intensity of the F →I laser transition increases with the treatment temperature and Nd content, whereas a reduction for the luminescence lifetime is observed compared to those observed in bulk samples prepared by melting quenching., This work was supported by MINECO sunder Projects No. MAT2013‐48246‐C2‐1‐P and MAT2013‐48246‐C2‐2‐P and Basque Country University PPG17/07. J.J. Velázquez also acknowledges MINECO under Grant FPDI‐2013‐16895.

Visible-to-UV/violet upconversion luminescence is found and studied in oxyfl uoride glass ceramics with Er 3+ dopant concentrations of 3.5, 6.0, or 12.0 mol%, covering a broad pump-power range. The glass ceramics with doping levels of 3.5 and 6.0 mol% show the strongest upconversion luminescence intensity when compared to both higher doping levels and the respective precursor glasses. A comprehensive analysis of the involved upconversion mechanisms is presented. These materials could be useful to enhance the effi ciency of the water-splitting systems by using UV/violet light upconverted from the green and red parts of the solar spectrum, which are an alternative to photovoltaic solar cells.

Lithium luminescent ZnO:Li nanocrystals have been synthesized. Atomic absorption and optical spectroscopy confirm the high doping level of Li up to 5 at% can be achieved and indicate that the dopants may form neutral Li–Li dimers. The 100 nm width and several milliseconds lifetime long luminescence of the proposed Li–Li dimers occurs around 770 nm and is excited by energy transfer from the ZnO host when pumped in the range between 250 and 420 nm. These parameters of Li-related luminescence have been explained in terms of the energy level diagram of Li–Li dimers, where the Li luminescence is excited by spin-allowed singlet–singlet transitions and occurs due to spin-forbidden triplet–singlet transitions of Li–Li dimers. The milliseconds lifetime of the emitting level of Li dimers and nanosecond lifetime of the feeding state of the ZnO point out a 3-level lasing system. This Li luminescence may be used for the broad spectral range down-conversion of solar spectrum for enhanced efficiency solar cells. The sites for the Li–Li dimers have been proposed, where Li atoms locate in octahedral voids of Zn and O sub-lattices.

95SiO 2 –5LaF 3 sol–gel derived nano-glass–ceramics single doped with Ce 3+ or Tb 3+ and co-doped with Ce 3+ –Tb 3+ were synthesized by thermal treatment of precursor glasses. Precipitation of LaF 3 nanocrystals during ceramming process was confirmed by X-ray diffraction with mean size ranging from 12 to 15 nm. An exhaustive spectroscopic analysis has been carried out. As a result, it was found that the green emission of Tb 3+ ions was greatly enhanced through down shifting process, due to efficient energy transfer from Ce 3+ to Tb 3+ ions in the glass–ceramics, which is favored by the reduction of the interionic distances when the dopant ions are partitioned into LaF 3 nanocrystals. These results suggest the use of these materials to improve the efficiency of solar cells.

95SiO2–5LaF3 sol-gel derived nano-glass-ceramics single doped with Eu3+ or Sm3+ and codoped with both of them were successfully obtained. XRD measurements confirm the precipitation of LaF3 nanocrystals after the ceramming process, with mean size ranging from 10 to 20 nm which increases with the thermal treatment temperature. The incorporation of rare-earth ions into precipitated LaF3 nanocrystals was confirmed from luminescence spectra. Intense yellow-red emissions were detected under UV and blue light excitation in single and codoped samples. The effect of codoping with Eu3+ and Sm3+ ions and the energy transfer mechanism between them have been analyzed in order to increase the yellow-red emissions.

Sol–gel derived glass–ceramics containing CeF3 nanocrystals have been developed for the first time, to the best of our knowledge, by adequate heat treatments of precursor bulk glasses with composition 95SiO2–5CeF3 doped with 0.1 Eu3+ or 0.1 Sm3+ and co-doped with 0.3 Yb3+ and 0.1 Er3+ ions (in mol%). X-Ray Diffraction and High Resolution Transmission Electron Microscopy confirm the precipitation of CeF3 nanocrystals. Moreover, this structural analysis is completed using Eu3+ and Sm3+ as probe ions of the different local environments for rare-earth ions in the nano-structured glass–ceramics. Luminescence measurements led us to discern the final environments for the ions, revealing the partition of a large fraction of these ions into like-crystalline environment of the precipitated CeF3 nanocrystals. Near infrared emission at 1.5 μm was observed after excitation at 980 nm in Yb3+–Er3+ co-doped samples for potential applications in telecommunications.

In this work, erbium and ytterbium have been incorporated into luminescent porous silicon (PS) layers by simple impregnation of the PS substrate with a saturated nitrate solution of erbium and ytterbium. The photoluminescence of the co-doped rare earth layers have been evaluated. The doping process has been designed for its potential in silicon-based solar cell production, with the aim to improve the Shockley–Queisser limit with a reasonable cost effective method for the industry, which implies a significant enhancement of the efficiency under non-concentrated sunlight irradiation. The temperature and annealing time of the doping process were selected according to industry standards in order to ease a trial adoption. The composition was analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy in order to characterize the doping profile. Different up-conversion and down-conversion contributions from the rare earths in the visible and IR were detected, together with the down shifting effect of the stain etched PS. There is no evidence of energy transference between the PS matrix and the rare earths.

Sol-gel glasses with composition (100−x)SiO2–xSnO2 doped with 0.4 mol% of Sm3+, with x ranging from 1 to 10, have been successfully synthesized. Transparent doped nano-glass-ceramics were prepared by thermal treatment of the precursor glasses at 900°C during 4 hours, leading to nanocomposites comprising SnO2 nanocrystals embedded into an amorphous SiO2 phase. A structural analysis in terms of X-ray Diffraction and High Resolution Transmission Electron Microscopy confirms the precipitation of SnO2 nanocrystals within the glassy matrix. The mean radius of the obtained SnO2 nanocrystals, ranging from 2.1 to 4.7 nm calculated by the Scherrer and Brus equations, similar to the Bohr’s exciton radius, constitutes a wide band-gap semiconductor quantum-dot system. Energy transfer from SnO2 nanocrystal host to Sm3+ ions is confirmed by luminescence spectra and analyzed as a function of SnO2 concentration, showing an evolution that could be ascribed to selective excitation of nanocrystal sets with predetermined size. Besides, a study of the luminescence as a function of temperature helps to clarify the involved energy transfer mechanisms.

Transparent nano-glass–ceramics of composition 95SiO 2 –5SnO 2 mol%, single doped with 0.4 mol% of Tb 3+ and co-doped with 0.4 mol% of Eu 3+ and Tb 3+ have been obtained by thermal treatment of precursor sol–gel glasses. The segregated SnO 2 nanocrystals, precipitated in the insulator SiO 2 glass matrix during heat treatment, constitute a wide band gap quantum-dot system with mean radius of nanocrystals around 2.2–2.8 nm, comparable to the bulk exciton Bohr radius. A fraction of the rare earth ions is incorporated to the SnO 2 nanocrystals and can be excited by energy transfer from the semiconductor host. The efficiency of this energy transfer process is strongly dependent on the nanocrystal radius in the case of the Tb 3+ ions, whereas the dependence is not appreciable in the case of Eu 3+ ions. These results can be explained taking into account the variations of the overlap of the SnO 2 broad visible emission due to oxygen vacancies with the rare earth excitation spectra.

Nanostructured transparent glass-ceramics with composition of 95SiO2–5LaF3 doped with 0.1 mol% of Tm3+ or co-doped with 0.1 mol% of Tm3+ and 0.3 mol% of Yb3+ were synthesized by thermal treatment of precursor sol–gel derived glasses. A comparative luminescence analysis in terms of different temperatures of thermal treatments has been carried out. Segregation of LaF3 nanocrystals in the matrix was con- firmed by X-ray diffraction. Blue and red efficient up-conversion emissions were observed under 980 nm excitation at room temperature. These results indicate partition of a significant fraction of co-dopants into the precipitated LaF3 nanocrystals. The mechanisms involved in the up-conversion emissions have been analyzed and can be ascribed to processes with two, three and four photons. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Transparent glass-ceramics with composition of 95SiO 2 -5LaF 3 doped with 0.1 mol% of Ho 3+ or co-doped with 0.1 mol% of Ho 3+ and 0.3 mol% of Yb 3+ were synthesized by thermal treatment of precursor sol-gel glasses. Segregation of LaF 3 nanocrystals in the matrix was confirmed from a structural analysis by means of X-ray diffraction. Blue, green and red efficient up-conversion emissions were observed under 980 nm excitation at room temperature. These results could be attributed to the partition of a fraction of Ho 3+ ions into the precipitated LaF 3 nanocrystals. Moreover, near infrared down-conversion at 1.2 μm is also observed. The mechanisms involved in the up-conversion emissions could be ascribed to a two- and three-photon process.

Ca3Sc2Si3O12 garnets doped with Ce3+ and Tb3+ ions were synthesized by a freeze-drying precursor method. The structural characterization was performed by X-ray diffraction (XRD) and Raman spectroscopy. Scanning Electron Microscopy (SEM) images of the calcined material were studied. High temperature treatments and doping with RE3+ ions resulted in a reduction of the secondary phases (Sc2O3) and an increase of the mean size of the nanocrystals, from 75 to 149 nm. These effects were confirmed by means of Raman spectra. Moreover, luminescence features of Ce3+ and Tb3+ doped samples indicated that these ions are effectively incorporated into the crystalline phase. In addition, the energy transfer processes between Ce3+ and Tb3+ ions in codoped garnets have been studied. (C) 2015 Elsevier B.V. All rights reserved.

Bulk oxyfluoride glasses co-doped with Ag nanoclusters and Yb3+ ions have been prepared by a melt quenching technique. When excited in the absorption band of the Ag nanoclusters between 300 to 500 nm, these glasses emit a broad band characteristic of the Ag nanoclusters between 400 to 750 nm as well as an emission band between 900 to 1100 nm, originating from Yb3+ ions. The intensity ratio of the Yb3+/Ag emission bands increases with the Ag doping level at a fixed concentration of Yb3+, indicating the presence of energy transfer mechanism from the Ag nanoclusters to the Yb3+ ions. Comparison of time-resolved decay kinetics of the luminescence in the respectively Ag nanocluster-Yb3+ co-doped and single Ag nanocluster doped glasses, hints towards an energy transfer from the red and infrared emitting Ag nanoclusters to the Yb3+ ions.

The effect of heat treatment on the structure and luminescence of Ag nanoclusters doped oxyfluoride glasses was studied and the implication for drawing the corresponding fibers doped with luminescent Ag nanoclusters has been proposed. The heat treatment results, first, in condensation of the Ag nanoclusters into larger Ag nanoparticles and loss of Ag luminescence, and further heat treatment results in precipitation of a luminescent-loss nano- and microcrystalline Ag phases onto the surface of the glass. Thus, the oxyfluoride fiber doped with luminescent Ag nanoclusters was pulled from the viscous glass melt and its attenuation loss was 0.19 dB/cm in the red part of the spectrum; i.e. near to the maximum of Ag nanoclusters luminescence band. The nucleation centers for the Ag nanoclusters in oxyfluoride glasses have been suggested to be the fluorine vacancies and their nanoclusters. ispartof: Optical Materials vol:34 issue:4 pages:616-621 status: published

In this work, for the first time, the photoluminescent emission and excitation spectra of non-textured layers and stain-etched porous silicon layers (PSLs) doped with high temperature annealed europium (Eu) are evaluated. The PSLs are evaluated as a host for rare earth ions and as an antireflection coating. The applied doping process, which consists in a simple impregnation method followed by a high-temperature annealing step, is compatible with the standard processes in the fabrication of solar cells. The results show down-shifting processes with a maximum photoluminescent intensity at 615 nm, related to the transition 5D0 → 7F2. Different initial concentrations of Eu(NO3)3 are evaluated to study the influence of the rare earth concentration on the photoluminescent intensity. The chemical composition and the morphology of Eu-doped PSLs are examined by means of x-ray dispersion spectroscopy, Fourier-transform infrared spectroscopy and scanning electron microscopy. These Eu-doped layers are considered to be applied as energy converters in silicon-based third generation solar cells.

Nano-glass-ceramics of composition 95SiO(2)-5SnO(2) doped with 0.4 Sm(3+) (mol%) were synthesized by the thermal treatment of precursor sol-gel glasses. Structural and luminescence measurements were carried out. The precipitated SnO(2) nanocrystals in the glass matrix constitute a wide bandgap quantum-dot system with size comparable to the bulk exciton Bohr radius. A site-selective excitation, by energy transfer from the semiconductor host, reveals that a fraction of the Sm(3+) ions are incorporated in the SnO(2) nanocrystals, whereas the rest remains in the silica glassy phase. An evolution in the Sm(3+) emission spectra has been observed when the SnO(2) nanocrystals are excited with different UV wavelengths, which has been ascribed to selective excitation of nanocrystal sets with predetermined size.