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Hybrid materials consisting of SiO2/CdS particles dispersed in poly(styrene-co-maleic anhydride) and poly(styrene-co-maleimide) have been synthesized and characterized. The polymer nanocomposites were synthesised in situ in the presence of previously prepared inorganic fillers (SiO2/CdS). The nanocomposites were synthesized with the use of as-prepared or surface-modified SiO2/CdS fillers. For both types of nanocomposites, the optical properties were evaluated and the observation of size quantization effects in the optical spectra is discussed. In this context, the influence of the inorganic fillers and polymer matrices on the optical properties of the final nanocomposites was investigated.

In situ ion-beam-induced luminescence measurements reveal a strong enhancement of the Cr3+ emission yield in electrically conductive chromium doped β-Ga2O3 single crystals upon proton irradiation. The observed effect can be explained based on the Fermi-level pinning caused by radiation defects. This pinning of the Fermi level activates deep carrier traps that can act as sensitizers of the Cr3+ emission. In agreement with this model, in semi-insulating samples, where the Fermi level lies deep in the bandgap, the Cr3+ emission is present already in as-grown samples, and no enhancement of its intensity is observed upon proton irradiation. The boost of the Cr3+ emission yield by irradiation, observed in conductive samples, is reversed by thermal annealing in argon at temperatures above 550 °C for 30 s. The results reveal a high potential of Cr-doped β-Ga2O3 for in situ and ex situ optical radiation detection and dosimetry. [ABSTRACT FROM AUTHOR]

We report the observation of slow emission bands overlapped with the near-band-edge steady-state luminescence of nominally undoped ZnO crystals. At low temperatures the time-resolved spectra are dominated by the emission of several high-energy bound exciton lines and the two-electron satellite spectral region. Furthermore, two donor-acceptor pair transitions at 3.22 and 3.238 eV are clearly identified in temperature-dependent time-resolved spectroscopy. These donor-acceptor pairs involve a common shallow donor at 67 meV and deep acceptor levels at 250 and 232 meV. [ABSTRACT FROM AUTHOR]

Er-related luminescence near 1.54 μm (∼805 meV) is observed under below band gap excitation at 4.2 K in GaN:Er and GaN:Er,O implanted samples. The spectrum of the recovered damage samples is a multiline structure. So far, these lines are the sharpest ones reported for GaN. Well-resolved green and red luminescences are observed in implanted samples. The dependence of luminescence on the excitation energy as well as the influence of different nominal fluence and annealing conditions is discussed. Combining the results obtained from photoluminescence and Rutherford backscattering spectrometry, different lattice sites for the optical active Er-related centers are identified. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Resonance Raman spectroscopy has been used to study multiphonon scattering on the overtones of fully symmetric LO phonons in the crystal lattice of Mn-doped ZnO nanorods. A relationship between the scattering intensity and defectness of nanorods is established, which is manifested by the presence of green luminescence. [ABSTRACT FROM AUTHOR]

Pulsed laser deposition without a catalyst is used to grow ZnO nanorods less than 10 nm in diameter. The structure of the rods is studied by Raman scattering during excitation in the visible and UV regions. The temperature dependences of exciton spectra and the behavior of green luminescence are investigated in the temperature range 10–280 K. At room temperature, the luminescence intensity of the ZnO nanorods in the exciton region is higher than the green luminescence intensity by a factor of 7.8. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, there has been a resurgence in the interest in the use of ZnO (E g ∼3.37eV) as a material for a wide range of opto-emitter applications spanning visible and short wavelengths. Bulk, thin films and nanomaterials obtained using different synthesis methods have been investigated for optoelectronic and biotechnological device applications. Nominally undoped bulk samples typically present a myriad-structured near-band-edge recombination, mainly due to free/bound excitons and donor–acceptor pair transitions. Furthermore, deep level emission due to intrinsic defects and extrinsic impurities, such as transition metal ions, are commonly observed in different grades of bulk ZnO samples. Undoped thin film and ZnO nanocrystal samples also present optically-active centres due to the presence of native and extrinsic defects. Continuing improvement in device performance hinges on improved understanding of the role of these defects present in ZnO samples. In this work a correlation between the optical centres was observed between nominally-undoped bulk, thin films and nanocrystal ZnO. We also observed a correlation between the structural properties and ion optical activation for single crystal samples which were intentionally-doped with rare earth ions (Tm, Er, Eu and Tb) either (a) by ion-implantation or (b) during synthesis. For the doped ZnO nanocrystals, intra-ionic recombination and XRD data suggest that the ions are in a crystalline environment. [Copyright &y& Elsevier]

Sapphire single crystals implanted with different fluences of cobalt and subjected to annealing treatments in vacuum and in air during 1 h at 1000 °C were studied by optical and structural techniques. At room temperature the absorption mainly occurs in the ultraviolet (UV) being the luminescence dominated by a UV/blue broad emission band and a highly structured red emission. Structural analysis indicates that metallic precipitates, CoAl 2 O 4 and CoO phases are present in the implanted and annealed samples depending either on the fluence and on the annealing atmosphere. The observed luminescence cannot be correlated with intra-ionic Co 2+ and Co 3+ in an Al 3+ site in the sapphire lattice and a tentative assignment of the observed emission lines to the presence of aggregates is made. [ABSTRACT FROM AUTHOR]

Single crystalline SrTiO 3 samples were implanted with Er ions of 150 keV at room temperature with fluences of 5×10 14 and 5×10 15 . Annealing treatments were carried out both in reducing and oxidising atmospheres to recover the implantation damage. Infrared 1.54 µm Er 3+ luminescence between the two lowest spin-orbit levels 4 I 13/2 → 4 I 15/2 as well as emission from higher excited states 4 S 3/2 → 4 I 15/2 , 4 F 9/2 → 4 I 15/2 and 4 S 3/2 → 4 I 13/2 were observed in the implanted samples with highest fluence, annealed either in air or in vacuum. Multiple site location of Er 3+ ion is discussed and compared with RBS/C and emission channelling results that indicate that Er goes to Sr and Ti sites. [ABSTRACT FROM AUTHOR]

Abstract: In the present work we investigate, the role of zinc oxide (ZnO) thin films passivating layer deposited by rf magnetron sputtering at room temperature on low (18%) and high (80%) porosity porous silicon (PS). The micro-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) analysis have been carried out to understand the effect of ZnO films coating on PS. A systematic investigation from Raman spectroscopy suggests the formation of a good quality ZnO wurtzite structure on PS. The photoluminescence (PL) measurements on PS and ZnO coated PS shows a red, blue and UV emission bands at around ∼1.8, ∼2.78 and ∼3.2eV. An enhancement of all PL emission bands have been achieved after ZnO films deposition on high porosity PS. [Copyright &y& Elsevier]

Abstract: We have produced and studied erbium doped nanocrystalline silicon thin films with different oxygen and hydrogen content in order to evaluate the influence of the matrix on the Er3+ emission and on the 0.89eV and 1.17eV bands. Films were grown by reactive magnetron sputtering on glass substrates under several different conditions (RF power, Er content and gas mixture composition) in order to obtain different microstructures. The structural parameters and the chemical composition of the samples were obtained by X-ray in the grazing incidence geometry, Raman spectroscopy and Rutherford back scattering analysis. Using X-ray technique combined with Raman spectroscopy information on the crystalline fraction and the average crystallite size of Si nanocrystals was obtained. Dependence of the 0.89eV and 1.17eV peaks in Si heterogeneous matrixes on the films crystallinity and O/H ratio has been analyzed. [Copyright &y& Elsevier]

Abstract: With two interfering pulses from the fourth harmonic of a Nd–YAG laser we burnt a periodic lattice structure into the surface of GaN thin films. The lattice period of this permanent grating could be controlled between less than one and several tens of microns. Above the decomposition threshold, nitrogen evades from the sample surface, and the residual metallic gallium accumulates in the form of tiny droplets at the surfaces. The patterned structure shows structural similarities with microcavities. The question arises if the residual metallic gallium may act as a partially reflecting mirror. To test this hypothesis, we studied the steady-state and transient photoluminescence through the modulation of light emerging from the ubiquitous broad “yellow” photoluminescence band. The microlattice is evidenced by energy-equidistant spontaneous emission enhancement peaks in the steady-state photoluminescence spectra. We suggest that the partial reflection due to the residual metallic gallium leads to the observed enhancement effect. [Copyright &y& Elsevier]

Abstract Al x Ga 1-x N (x = 0.20) layers grown on (0001) sapphire substrates by metal organic chemical vapour deposition were implanted with terbium (Tb) ions at 150 keV with a fluence of 7 × 1014 Tb cm−2 at different temperatures. After thermal annealing, all layers evidenced the Tb-related 5D 4 -7F J intra-4 f 8 transitions, demonstrating an enhancement of their intensity with increasing implantation temperature. A detailed spectroscopic analysis of the optical properties of these layers was conducted using luminescence techniques. An atypical behaviour for the relative intensity of both the broad visible band and the intraionic lines was found as a function of temperature and its origin is discussed based on potential fluctuation phenomena and energy transfer processes. The 5D 4 -7F J intra-4 f 8 transitions exhibit thermal population with increasing temperature between ∼100 K and ∼200–230 K, with a subsequent decrease up to RT due to further competitive non-radiative recombination paths. The values calculated for the population energies of each sample are in good agreement with the ones obtained for the activation energies of the de-excitation of the yellow broad band also present in the spectra, suggesting a correlation between the host defect de-excitation processes and the population of the ion emitting levels. [ABSTRACT FROM AUTHOR]

Abstract AlGaN/GaN-superlattice based diode structures under study were grown by metal organic chemical vapour deposition, then implanted with two different Eu ion beam fluences, and further submitted to high temperature and high pressure thermal annealing treatments. The effects of Eu implantation and annealing on the diode structure emission characteristics were investigated at 14 K and room temperature. Eu3+ luminescence was observed in both Eu-implanted and annealed samples, being the most intense emission assigned to the 5D 0 → 7F 2 transition in the red spectral region (~621 nm), in line with the main observed behaviour of Eu3+ ions implanted in GaN layers. The combined excitation/emission spectra revealed that the measured intraionic emission corresponds to an overlap of two principal emitting centres which can be excited through above and below GaN bandgap. In addition, a considerable reduction of the non-radiative channels was observed for the diode structure implanted with the highest Eu fluence, inducing a higher thermal stability of the intra-4 f 6 lines intensity. In contrast to GaN layers, the perceived Eu3+ red emission observed at room temperature was found to be strongly sensitive to the GaN above bandgap excitation (out of the resonance conditions) suggesting that additional energy transfer between the AlGaN/GaN superlattice excitons and the Eu3+ ions occurs, therefore widening the excitation pathways for the red luminescence. Highlights • Eu implantation/annealing effects on AlGaN/GaN-superlattice diode optical properties. • Implantation/annealing conditions favour the multiple Eu3+ centre optical activation. • Higher thermal stability of the intra-4 f 6 lines for the highest Eu fluence diode. • Faster decay obtained for the yellow luminescence versus red Eu3+ luminescence. • The 325 nm excitation is the most efficient for providing the perceived red emission. [ABSTRACT FROM AUTHOR]

Rare earth orthosilicates are among the most widely used scintillator materials in the last decades. Particularly, lutetium-yttrium oxyorthosilicate (LYSO) is known to exhibit great potentialities in the field of radiation detectors for medical imaging. Consequently, an in-depth knowledge of the material properties is of utmost interest for the mentioned applications. In this work the spectroscopic properties of commercial cerium doped lutetium-yttrium oxyorthosilicate crystals (LYSO:Ce) were investigated by Raman spectroscopy, steady state photoluminescence, photoluminescence excitation and time resolved photoluminescence. Site selective excitation was used under steady state (325 nm) and pulsed (266 nm) conditions to separately investigate the temperature dependence of the 5d → 4f Ce 1 and Ce 2 luminescence, allowing to establish the thermal quenching dependence of the Ce 2 optical center. In the case of the Ce 1 optical center, a luminescence quantum efficiency of 78% was obtained from 14 K to room temperature with 266 nm photon excitation. [ABSTRACT FROM AUTHOR]

Abstract: With a 4f 6 electronic configuration, europium ions in the trivalent charge state are known to be efficient activators in wide band gap matrices. Embedded in the aluminophosphate (Li2O–BaO–Al2O3–La2O3–P2O5) glasses the optically activated Eu3+ ions lead to intense room temperature orange/red luminescence with 16–23Cd/m2 by using ultraviolet pumping. The as-prepared and heat treated europium doped glasses for temperatures below and above T g were studied by room temperature Raman spectroscopy, absorption, photoluminescence excitation, temperature dependent and time dependent photoluminescence. When the samples are excited by 325nm wavelength photons, an enhancement of the red luminescence intensity by ca. one order of magnitude was found to occur for temperatures between 14K and 350K, for all the doped glasses. On the other hand, by using resonant excitation on the 5L6 Eu3+ excited state (λ exc~390nm) the ion emission intensity was found to be nearly constant for temperatures up to 500K. For higher temperatures a steeper decrease of the luminescence intensity occurs due to non-radiative competitive channels described by activation energies of ca. 235meV and 450meV by using 325 and 390nm wavelength photons as excitation, respectively. The lifetime of the 5D0 level in these glasses is ca. 2.93ms. A discussion of the thermal population and de-excitation mechanisms is performed. [Copyright &y& Elsevier]

Abstract: Lanthanide doped zirconia based materials are promising phosphors for lighting applications. Transparent yttria stabilized zirconia fibres, in situ doped with Pr3+ ions, were grown by the laser floating zone method. The single crystalline doped fibres were found to be homogeneous in composition and provide an intense red luminescence at room temperature. The stability of this luminescence due to transitions between the 1D2 → 3H4 multiplets of the Pr3+ ions (intra-4f 2 configuration) was studied by photo- and iono-luminescence. The evolution of the red integrated photoluminescence intensity with temperature indicates that the overall luminescence decreases to ca. 40% of the initial intensity at 14K when heated to room temperature (RT). RT analysis of the iono-luminescence dependence on irradiation fluence reveals a decrease of the intensity (to slightly more than ∼60% of the initial intensity after 25min of proton irradiation exposure). Nevertheless the luminescence intensity saturates at non-zero values for higher irradiation fluences revealing good potential for the use of this material in radiation environments. [Copyright &y& Elsevier]

Abstract: Samples of Nb2O5 were prepared by laser floating zone (LFZ) technique and by solid-state reaction in order to study some of their physical properties as a function of synthesis conditions. Single crystals fibres were obtained by LFZ, while a structural orthorhombic to monoclinic phase transition was observed in samples sintered at temperature higher than 800°C. Transmission optical spectroscopy and photoconductivity measurements allowed identifying a ∼3.2eV bandgap energy for the H-Nb2O5 monoclinic crystalline phase. Band gap shrinkage of ∼100meV was observed from 14K to RT. For the orthorhombic phase (T-Nb2O5), the photoconductivity measurements evidence a higher energy bandgap. The sintered samples have shown a broad recombination luminescence band at the orange/red spectral region while no luminescence was detected from the LFZ grown fibres. A dielectric constant of ∼40 was found for the 800°C and 1200°C sintered pellets while that of 1000°C reached four times that value. [ABSTRACT FROM AUTHOR]

Abstract: The effects of the AlN molar fraction on structural and optical properties of praseodymium implanted Al x Ga1− x N (0⩽x⩽1) layers were investigated. Using photoluminescence and excitation luminescence techniques we are able to observe the intra-4f2 3P1→3H5 (526nm) and 3P0→3F2 (652nm) transitions of the Pr3+ ion. The red emission peak position shifts to lower energies with increasing Al content in the alloys. The peak full-width at half-maximum increases with the Al content up to x=0.7 due to disorder effects. The implantation damage and Pr-incorporation was investigated by Rutherford backscattering spectrometry doing channelling measurements along the 〈0001〉 direction. X-ray diffraction reciprocal space maps show an expansion of the c lattice parameter in the implanted region which is reversed after thermal annealing at 1300°C. [Copyright &y& Elsevier]

Abstract: This work shows a comparative study of organic light emitting diodes based on four different europium complexes with the general formula, Eu(CLs)3bipyridine, where the central ligands are DBM [tris(dibenzoylmethane)], TTA [tris(1-(2-thieneyl)-4,4,4-trifluoro-1,3-butanedione)], NTA [tris(1-(2-naphthoyl)-3,3,3-trifluoroacetone)] and BTA [tris(1-(2-benzoyl)-3,3,3-trifluoroacetone)]. All devices have a driving voltage of 14–16V, a very low electrical current at normal operation (less than 1mA) and a good Wall Plug Efficiency (up to near 10−3%). The most suitable central ligand was found to be DBM, with an optical power up to 200nW (at 612nm). The BTA exhibits the lowest stability under high applied voltages. The other central ligands have similar results among them. The electroluminescence spectra clearly show the europium ion transitions (with a strong 5D0 → 7F2 line) with a CIE color coordinate around (0.56, 0.34). [Copyright &y& Elsevier]

Abstract: In this work, a ruthenium hexafluorophosphate complex, [Ru(bpy)3](PF6)2 in poly(methylmethacrylate) (PMMA) was employed to build a single layer light electrochemical cell on indium tin oxide polyester flexible substrate. The electroluminescence spectrum features a relatively broad band peaked near 625nm, with CIE (x, y) color coordinates of (0.61,0.39). The driving voltage is only 3V, and for the maximum electrical current of 10mA the brightness reaches 1cd/m2. Regarding the useful application of the device, its opto-electrical behavior under mechanical strain was studied considering the central curvature. In these situations, both electrical characterization in DC mode and luminance were analyzed. [Copyright &y& Elsevier]

Abstract: GaN epilayers grown by MOCVD were implanted with Tm and Eu under different implantation conditions, in order to optimize the implantation parameters of fluence, implantation temperature and energy. Rutherford backscattering spectrometry in the channelling mode (RBS/C), scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-dependent photoluminescence (PL) and room temperature cathodoluminescence (CL) were used to study structural and optical properties of the samples. Different annealing methods are compared. According to RBS/C measurements, Tm at low fluences is found to incorporate entirely on substitutional Ga-sites while for higher fluences the substitutional fraction decreases. Increasing the fluence leads to increasing damage levels and finally to the formation of a partially amorphous, nanocrystalline surface layer. The luminescence intensity increases with fluence at first. However, for fluences in excess of 2×1015 Tm/cm2 it decreases again, showing a strong correlation between structural and optical properties. Implanting at higher temperature inhibits the formation of the nanocrystalline layer and increases both the substitutional fraction and the luminescence intensity. We also found that the presence of a thin AlN cap protects the sample during post-implant high temperature annealing and prevents the formation of a nanocrystalline surface layer during the implantation even for high fluences. The intensity of Eu-related CL near 622nm at room temperature increases by a factor of 40 within the studied annealing range from 1000 to 1300°C. [Copyright &y& Elsevier]

Abstract: Zinc oxide single crystals were implanted with Tm and Er ions in a wide range of fluences. For both types of ions RBS/channeling shows for the as-implanted state the same minimum yield as for the host. Damage recovery becomes significant for annealing above 750°C and is almost complete at 1050°C. Implantation damage decreases for implantations at mild temperatures (450°C) and is also highly reduced for 〈0001〉 aligned implantations: under this condition the measured minimum yield is about one order of magnitude lower compared to the random implantations. The RE ions start to diffuse towards the surface above 900°C and about 80% of them have segregate to the surface after 90min annealing at 1050°C. A small fraction of the ions retained in the implanted region is located in regular lattice sites. In the as-implanted state the optical activity of the RE ions is highly quenched by the implantation defects. For all the RE studied, diffusion to the surface destroys the luminescence. Photoluminescence (PL) studies for Er implantations reveal in the as-implanted and annealed samples the presence of a weak emission near 1.54μm due the 4I13/2 → 4I15/2 transition of the Er3+ ions. [Copyright &y& Elsevier]

Abstract: ZnO single crystals implanted with different fluences of thulium ions and subject to different annealing conditions present multiple-Tm related optical centres. After implantation, the Tm ions are incorporated in a highly damaged region, some of them being placed at Zn sites (SZn). Following annealing, the optical activation of Tm ions is accompanied by a progressive lattice recovery. The main intraionic luminescence, observed with above band gap excitation, is dominated by the near infrared emission due to the transition and can be observed up to near RT. [Copyright &y& Elsevier]

This paper reviews the current knowledge on rare earths (REs) implanted into GaN with a special focus on their lattice location and on the optical activation by means of thermal annealing. While emission channeling experiments have given information on the lattice location of rare earths following low-dose (≈1013 cm−2) implantation, both in the as-implanted state and after annealing up to 900 °C, the lattice location of higher-dose implants (1014–1015 cm−2) and their defect annealing behaviour were studied using the Rutherford backscattering/channeling (RBS/C) method. The available channeling and luminescence results suggest that the optical activation of implanted REs in GaN is related to their incorporation in substitutional Ga sites combined with the effective removal of the implantation damage. [Copyright &y& Elsevier]

Abstract: The room temperature spectroscopic properties of terbium doped zirconia fibres grown by Laser Floating Zone method are reported. The fibres were found to be stabilised in the tetragonal crystalline phase as measured by X-ray diffraction and Raman spectroscopy techniques. The doping with terbium ions was performed during the growth process and their incorporation on the wide band gap oxide host assumes an important role on the stabilisation of the high temperature tetragonal crystalline phase. Under ultraviolet optical pumping a bright green luminescence was observed by naked eye at room temperature, corresponding to the 4f →4f transitions between the crystal-field split energy levels of the 5D4 and 7F5 manifolds of the 4f 8 electronic configuration of the Tb3+ ions. These results suggest that YSZ:Tb3+ could be considered as a promising candidate for applications in green electroluminescent devices. [Copyright &y& Elsevier]

Abstract: Transparent SiO2:Li2O:Nb2O5 glass doped with Tm3+ has been prepared by the sol–gel method, and heat-treated in air (HT) at temperatures between 500 and 800°C. X-ray diffraction (XRD) patterns and Raman spectroscopy show SiO2 and LiNbO3 phases in samples HT above 650°C, and a NbTmO4 phase for T >750°C. The XRD SEM analysis show increasing particle size and number with the increase of HT temperature. Intra-4f12 transitions due to Tm3+ ion dispersed in the matrix are observed in samples with T >650°C. The luminescence is dominated by the 1G4 → 3F4 (∼650nm), 1D2 → 3F3 (∼780nm), 3H4 → 3H6 (∼800nm), 3H5 → 3H6 (∼1200nm) and 3H4 → 3F4 (∼1500nm) transitions under resonant excitation to the ion levels. [Copyright &y& Elsevier]

• A new optical glass, 20B 2 O 3 -50P 2 O 5 -10Li 2 O-9Al 2 O 3 -5ZnO-3Dy 2 O 3 -3Tb 2 O 3 was obtained. • metaphosphate structure - boron oxide [BO 3 ] Q2 units - (P O B) bonds are identified. • SEM/EDS revealed that both dopants Dy 2 O 3 and Tb 2 O 3 are uniformly distributed. • PLE, TRPL and lifetime indicate energy transfer Dy3+ - Tb3+ at significant rate. A new optical glass with the molar composition 20B 2 O 3 -50P 2 O 5 -10Li 2 O-9Al 2 O 3 -5ZnO-3Dy 2 O 3 -3Tb 2 O 3 was obtained by melting-quenching technique comprising wet route raw materials preparation, and the structural and optical characteristics of the glass were investigated by different experimental techniques. The amorphous nature was confirmed by X-ray diffraction (XRD) and the thermal stability was assessed by differential thermal analysis (DTA). Information about the defects of the co-doped glass as well as about the elemental compositional homogeneity was revealed by scanning electron microscopy/energy dispersive spectrometry (SEM/EDS). Structural information provided by Fourier Transform Infrared (FTIR) and Raman spectroscopy indicated metaphosphate structure of the glass together with boron oxide mostly in [BO 3 ] Q2 units and also P O B bonds. Ultraviolet–visible (UV–Vis) absorbance, photoluminescence (PL), photoluminescence excitation (PLE) and time resolved photoluminescence (TRPL) spectra and luminescence decay curve were investigated systematically. Energy transfer process between Dy3+ and Tb3+ ions and its influence on luminescent properties were discussed. Normalized RT PL of the Dy/Tb co-doped glass sample, obtained with 301, 316, 353 and 384 nm wavelength excitation. The transitions involving states which J is integer correspond to Tb3+ and which J is half integer correspond to Dy3+. Image, graphical abstract [ABSTRACT FROM AUTHOR]