Ramzi Maalej | University of Sfax (original) (raw)
Papers by Ramzi Maalej
Applied Surface Science, 2021
© 2021 Elsevier B.V.The choice of substrate is crucial for device applications, in particular for... more © 2021 Elsevier B.V.The choice of substrate is crucial for device applications, in particular for atomically thin materials such as monolayer transition metal dichalcogenides. The interaction between the active material and the substrate could be exploited to improve the device performance. In this work, we used a Sm-doped aluminosilicate glass (Sm-ASG) as a substrate for monolayer MoS2 based photodetector. Due to the strong high-energy emission lines of Sm, Sm-ASG substrate absorbs the incident light and acts as second excitation source compensating the low absorption of the MoS2 monolayer. On Sm-ASG substrate, the MoS2 photoresponsivity was increased up to 13,157 AW−1 as compared to 5,740 AW−1 on undoped ASG substrate, under illumination of a monochromatic laser with 520 nm wavelength at a power of 0.2 µW. The significantly enhanced photoresponse, which is amongst the highest reported values for unbiased photoconductors, is attributed to the dual function of Sm-ASG substrate, consisting of a surface charge transfer and an enhanced photoexcitation via a photon recycling effect. Our new approach, based on the simple use of substrate, paves the way for achieving high performance optoelectronic devices.11Nsciescopu
Journal of Rare Earths, 2015
Abstract Ho3+ ions doped tellurite-borate glass samples with varying compositions were prepared. ... more Abstract Ho3+ ions doped tellurite-borate glass samples with varying compositions were prepared. The compositional dependence on phenomenological Judd-Ofelt parameters was compared in different kinds of rare earth ions doped tellurite-borate glasses. Two methods were used to obtain radiative transition probability of 5I7 level with the aim of assuring the fitting quality. The integral absorption cross-sections and line shapes corresponding to 5I8→5G6 and 5I8→5I7 transition of Ho3+ ions were investigated in tellurite-borate glasses. The obtained data indicated that the integral absorption cross-sections corresponding to 5I8→5G6 transition of Ho3+ ions mainly depended on phenomenological Judd-Ofelt parameter, Ω2, because 5I8→5G6 transition belonged to hypersensitive transitions, which led to a larger Ω2 value. The change of line shapes of absorption spectra corresponding to 5I8→5G6 and 5I8→5I7 transitions of Ho3+ ions came from the lower energy regions, which could be attributed to the changed distribution of Stark levels and thermal population.
Methods and Applications in Fluorescence
A series of green emitting Gd2O3:Tb3+ (Tb: 0%–10% mol) nanoparticles (NP) were synthesized using ... more A series of green emitting Gd2O3:Tb3+ (Tb: 0%–10% mol) nanoparticles (NP) were synthesized using the hydrothermal method, then characterized and evaluated for latent fingerprint visualization. X-ray diffraction study (XRD) revealed a cubic structure of the nanoparticles and the total incorporation of the terbium in the Gd2O3 matrix. Field Emission-Scanning Electron Microscopy (FESEM), Energy Dispersive x-ray Spectrometry (EDX) and Transmission Electron Microscopy (TEM) were used to study the morphology and the elementary composition of the NP. Photoluminescence (PL) studies showed strong green emission around 540 nm due to the transition 5D4 → 7F5. The luminescence color of the synthesized NP was characterized by the CIE 1931 chromaticity diagram. The potential use of the NP powders for the visualization of latent fingerprint under UV irradiation was assessed on various substrates. The latent fingerprint images revealed by the Gd2O3:Tb3+ NP powders are clear enough to extract and analyze reliable fingerprint features. The fingerprint quality was evaluated using three fingerprint quality assessment metrics and by extracting and measuring the visibility of the minutiae. The experimental results show very good quality images of the latent fingerprint acquired using the Gd2O3:Tb3+ NP and yield good minutiae extraction.
Optical Materials Express
Fitting optical properties of metals is of great interest for numerical methods in electromagneti... more Fitting optical properties of metals is of great interest for numerical methods in electromagnetism, especially finite difference time domain (FDTD). However, this is a tedious task given that theoretical models used usually fail to interlink perfectly with the experimental data. However, in this paper, we propose a method for fitting the relative permittivity of metals by a sum of Drude-Lorentz or a sum of partial-fraction models. We use the particle swarm optimization (PSO) hybridized either with Nelder-Mead downhill simplex, or with gradient method. The main electronic transitions in metals help to guide the fitting process toward the solution. The method is automatic and applied blindly to silver, gold, copper, aluminum, chromium, platinum, and titanium.
Physica B: Condensed Matter
Abstract Er3+ doped, Yb3+ doped, and Er3+/Yb3+ co-doped Y2Ti2O7 phosphors with various concentrat... more Abstract Er3+ doped, Yb3+ doped, and Er3+/Yb3+ co-doped Y2Ti2O7 phosphors with various concentrations of Er3+ (12–20%), Yb3+ (1-10 at%), and Er3+Yb3+ (1%, and 1,2,3%, respectively) were prepared by solid-state reaction. The phase structure and purity of all prepared phosphors were studied by X-ray diffraction analysis followed by measurement of the hydrodynamic diameter of each sample by Dynamic light scattering. The formation of the pyrochlore structure was confirmed by the observation of relative vibrations by Fourier Transform Infrared Spectroscopy. Moreover, photoluminescence spectra of different co-doped Y2Ti2O7 compounds are presented to check the energy transfer processes of Er3+ and Yb3+ ions. Finally, phosphors were used for the detection of latent fingermarks on various surfaces and a fingerprint minutia extraction algorithm was used for the analysis of extracted minutiae. The analyses confirm that the co-doped phosphors can be useful for the visualization of latent fingerprints once a good detection of their minutiae is obtained.
Sensors and Actuators B: Chemical, 2017
The luminescence characteristics of GaN films implanted with Erbium at low doses were evaluated. ... more The luminescence characteristics of GaN films implanted with Erbium at low doses were evaluated. The temperature dependence of the YL band allowed us to identify the nitrogenvacancy as the main responsible defect for this emission. The color coordinates analysis indicates that Er 3+ /Yb 3+ co-doped GaN semiconductor emits at room temperature a blended light with color in the white-light region. The significant temperature sensitivity obtained indicates its potential as optical temperature sensing probe in the temperature range 200-300K. The maximum sensitivity reached was 15x10-4 K-1 at 200 K.
ABSTRACT ESBM 2013-CONFERENCE PROGRAM
Journal of Luminescence, 2015
ABSTRACT Abstract In this paper, a new tellurite glass (85TeO2·5.0Nb2O5· 5.0ZnO·5.0LiF) doped wit... more ABSTRACT Abstract In this paper, a new tellurite glass (85TeO2·5.0Nb2O5· 5.0ZnO·5.0LiF) doped with 1 mol% Tm2O3 was prepared by melt-quenching technique. Differential scanning calorimetry (DSC) measurements indicate a good thermal stability, X-ray diffraction patterns show no sign of crystallization. Precise refractive index measurements were performed on five different wavelengths by a prism spectrometer. The optical energy gap, the Sellmeier energy gap and the dispersion energy were estimated. Judd–Ofelt intensity parameters were evaluated in order to obtain electric and magnetic-dipole transition probabilities, branching ratios and radiative lifetimes of several excited states of Tm3+. The classical McCumber theory was used to evaluate the emission cross-sections for the 3F4→3H6 transition at a wavelength of around 1.8 µm. The characteristics of down-conversion luminescence in the visible range were studied by exciting Tm3+ ions into the 1G4 level. Furthermore the structure of this glass was analyzed by Raman spectroscopy.
IEEE Transactions on Nanobioscience, 2017
Engineering Sciences for Biology and Medicine (ESBM) is an exciting platform for researchers to d... more Engineering Sciences for Biology and Medicine (ESBM) is an exciting platform for researchers to discuss a wide range of modern biology and medicine goals. The third edition ESBM 2017 conference was organized by the Tunisian Association of Academic Researchers ATCU, in collaboration with the Technopark of Sfax and the Digital Research Centre of Sfax from May 4–7’ 2017 in Sfax, Tunisia. This conference encourages the scientific interactions among researchers to share their ideas and approaches on all aspects of glitches in biology and medicine. Editors thank all the participants for their contributions, that are greatly appreciated. This special section consists of selected peer-reviewed papers on 1) Nanobiotechnology and Nanomedicine, 2) Systems Biology and Forensics, 3) Health Data & Models, 4) Health Data Processing, 5) Devices, Infrastructure & Communication, and 6) e-Health Services and Applications that highlight current developments. The ESBM 2017 conference received a total of...
IEEE Transactions on NanoBioscience, 2015
Submission Deadline 30/01/2015 Call for papers ESBM 2015 The international conference " Engi... more Submission Deadline 30/01/2015 Call for papers ESBM 2015 The international conference " Engineering Sciences in Biology and Medicine" ESBM'2015 will be organized in Monastir- Tunisia from 01 to 03 Mai 2015. You are invited to submit your abstract by 30 January 2015. Selected high quality research papers will be considered for publication after peer review in a special issue of the following journals: Advanced Science Letters (IF= 1.253) IEEE Transactions on NanoBioscience (IF= 1.768) For more details visit the conference website: http://www.esbm2015.com/
Journal of Photochemistry and Photobiology A Chemistry
New photoluminescent, non-toxic europium doped yttrium titanate phosphors (x mol% Eu3+/Y2Ti2O7 wh... more New photoluminescent, non-toxic europium doped yttrium titanate phosphors (x mol% Eu3+/Y2Ti2O7 where x = 1.0, 2.0, 4.0 6.0, 10, 15 and 30 mol%) with high crystalline structure were synthesized by sol–gel followed by heat treatment at 1000 °C for 5 h. Eu3+/Y2Ti2O7 phosphors were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), FT-IR and photoluminescence (PL) spectroscopy. The effects of heat treatment and europium metal ion concentration on the structure and PL properties were investigated. Eu3+/Y2Ti2O7 phosphors exhibited micro spherical shape with average crystal size from 90 to 144 nm. The PL spectra showed the orange red emission bands of Eu3+ in highly symmetrical host. The longest PL lifetime was detected at 4 mol% Eu3+/Y2Ti2O7 phosphor. The toxicity of 15 mol% Eu3+:Y2Ti2O7 was tested. The obtained result showed LD50 is 3.2 g/kg. The PL and toxicity properties of the prepared phosphors make them promising m...
Journal of Applied Physics, 2015
RSC Adv., 2015
ZnO:Er 3+ ,Yb 3+ thin films with a hexagonal wurtzite structure were successfully deposited on Si... more ZnO:Er 3+ ,Yb 3+ thin films with a hexagonal wurtzite structure were successfully deposited on Si (111) substrates at 430 C by an aerosol-assisted chemical vapor deposition (AACVD) atmospheric pressure process. The films were deposited with fixed 3 mol% erbium concentration and various ytterbium concentrations of 6, 8, 9 and 10 mol%. The annealing treatment at 1000 C was found to enhance the crystallinity and the upconversion (UC) emission of the films. UC emissions were investigated under 980 nm excitation, and the ZnO:Er 3+ ,Yb 3+ films exhibited the intense red 665 nm upconverted emissions of Er 3+ ions originating from an efficient Yb-Er energy transfer process. The absolute upconversion Quantum Yield (UC-QY) of each film was measured for the UC emissions centered at 410, 540 and 665 nm at varying excitation power densities. UC-QY analysis has revealed that the ZnO:3 mol% Er,9 mol% Yb thin film possesses the highest total quantum yield of 5.59 AE 0.1% with a power density of 19.3 AE 3 W cm À2 . These results show that this film is promising as an efficient upconversion layer suitable for many photonic applications.
Journal of Alloys and Compounds
This research work is a detailed study of the effect of deposition conditions on the combined lig... more This research work is a detailed study of the effect of deposition conditions on the combined light trapping and photon conversion properties of Nd 3þ ions doped ZnO nanodisk thin films. Hexagonal wurtzite phased ZnO:Nd films were deposited at the temperature range of [370e500 C] by aerosol assisted chemical vapor deposition (AACVD) process at atmospheric pressure. Actually, annealing treatment at 1000 C in air atmosphere led to the increase of crystallinity, decrease of the porosity of the films and enhancement of their optical properties. Moreover, this work has demonstrated that annealing strongly modifies the local structure and the crystal field of the Nd 3þ ions embedded in ZnO, leading to a high efficiency of visible-to-infrared downconversion (DC) emissions. The optimized 2.805 at.% Nd embedded in ZnO shaped nanodisk thin film exhibits a strong and resolved 920 and 1060 nm DC emissions. In addition, this film presents a low reflectance percentage of 17.1% with average external quantum efficiency (EQE) of 51.0% in the [400e800 nm] range, leading to an improvement of quantum efficiency of 12.5%. These findings show that the combined photon conversion and light trapping properties in semiconducting ZnO:Nd nanodisk shaped thin film is a well known passive approach that can boost c-Si solar cells efficiency.
Nanoscale Research Letters, 2015
We synthesized Gd 2 O 3 and Gd 2 O 3 doped by europium (Eu) (2% to 10%) nanoplatelets using the p... more We synthesized Gd 2 O 3 and Gd 2 O 3 doped by europium (Eu) (2% to 10%) nanoplatelets using the polyol chemical method. The synthesized nanoplatelets were characterized by X-ray diffraction (XRD), FESEM, TEM, and EDX techniques. The optical properties of the synthesized nanoplatelets were investigated by photoluminescence spectroscopy. We also studied the magnetic resonance imaging (MRI) contrast enhancement of T1 relaxivity using 3 T MRI. The XRD for Gd 2 O 3 revealed a cubic crystalline structure. The XRD of Gd 2 O 3 :Eu 3+ nanoplatelets were highly consistent with Gd 2 O 3 indicating the total incorporation of the Eu 3+ ions in the Gd 2 O 3 matrix. The Eu doping of Gd 2 O 3 produced red luminescence around 612 nm corresponding to the radiative transitions from the Eu-excited state 5 D 0 to the 7 F 2 . The photoluminescence was maximal at 5% Eu doping concentration. The stimulated CIE chromaticity coordinates were also calculated. Judd-Ofelt analysis was used to obtain the radiative properties of the sample from the emission spectra. The MRI contrast enhancement due to Gd 2 O 3 was compared to DOTAREM commercial contrast agent at similar concentration of gadolinium oxide and provided similar contrast enhancement. The incorporation of Eu, however, decreased the MRI contrast due to replacement of gadolinium by Eu.
Applied Surface Science, 2021
© 2021 Elsevier B.V.The choice of substrate is crucial for device applications, in particular for... more © 2021 Elsevier B.V.The choice of substrate is crucial for device applications, in particular for atomically thin materials such as monolayer transition metal dichalcogenides. The interaction between the active material and the substrate could be exploited to improve the device performance. In this work, we used a Sm-doped aluminosilicate glass (Sm-ASG) as a substrate for monolayer MoS2 based photodetector. Due to the strong high-energy emission lines of Sm, Sm-ASG substrate absorbs the incident light and acts as second excitation source compensating the low absorption of the MoS2 monolayer. On Sm-ASG substrate, the MoS2 photoresponsivity was increased up to 13,157 AW−1 as compared to 5,740 AW−1 on undoped ASG substrate, under illumination of a monochromatic laser with 520 nm wavelength at a power of 0.2 µW. The significantly enhanced photoresponse, which is amongst the highest reported values for unbiased photoconductors, is attributed to the dual function of Sm-ASG substrate, consisting of a surface charge transfer and an enhanced photoexcitation via a photon recycling effect. Our new approach, based on the simple use of substrate, paves the way for achieving high performance optoelectronic devices.11Nsciescopu
Journal of Rare Earths, 2015
Abstract Ho3+ ions doped tellurite-borate glass samples with varying compositions were prepared. ... more Abstract Ho3+ ions doped tellurite-borate glass samples with varying compositions were prepared. The compositional dependence on phenomenological Judd-Ofelt parameters was compared in different kinds of rare earth ions doped tellurite-borate glasses. Two methods were used to obtain radiative transition probability of 5I7 level with the aim of assuring the fitting quality. The integral absorption cross-sections and line shapes corresponding to 5I8→5G6 and 5I8→5I7 transition of Ho3+ ions were investigated in tellurite-borate glasses. The obtained data indicated that the integral absorption cross-sections corresponding to 5I8→5G6 transition of Ho3+ ions mainly depended on phenomenological Judd-Ofelt parameter, Ω2, because 5I8→5G6 transition belonged to hypersensitive transitions, which led to a larger Ω2 value. The change of line shapes of absorption spectra corresponding to 5I8→5G6 and 5I8→5I7 transitions of Ho3+ ions came from the lower energy regions, which could be attributed to the changed distribution of Stark levels and thermal population.
Methods and Applications in Fluorescence
A series of green emitting Gd2O3:Tb3+ (Tb: 0%–10% mol) nanoparticles (NP) were synthesized using ... more A series of green emitting Gd2O3:Tb3+ (Tb: 0%–10% mol) nanoparticles (NP) were synthesized using the hydrothermal method, then characterized and evaluated for latent fingerprint visualization. X-ray diffraction study (XRD) revealed a cubic structure of the nanoparticles and the total incorporation of the terbium in the Gd2O3 matrix. Field Emission-Scanning Electron Microscopy (FESEM), Energy Dispersive x-ray Spectrometry (EDX) and Transmission Electron Microscopy (TEM) were used to study the morphology and the elementary composition of the NP. Photoluminescence (PL) studies showed strong green emission around 540 nm due to the transition 5D4 → 7F5. The luminescence color of the synthesized NP was characterized by the CIE 1931 chromaticity diagram. The potential use of the NP powders for the visualization of latent fingerprint under UV irradiation was assessed on various substrates. The latent fingerprint images revealed by the Gd2O3:Tb3+ NP powders are clear enough to extract and analyze reliable fingerprint features. The fingerprint quality was evaluated using three fingerprint quality assessment metrics and by extracting and measuring the visibility of the minutiae. The experimental results show very good quality images of the latent fingerprint acquired using the Gd2O3:Tb3+ NP and yield good minutiae extraction.
Optical Materials Express
Fitting optical properties of metals is of great interest for numerical methods in electromagneti... more Fitting optical properties of metals is of great interest for numerical methods in electromagnetism, especially finite difference time domain (FDTD). However, this is a tedious task given that theoretical models used usually fail to interlink perfectly with the experimental data. However, in this paper, we propose a method for fitting the relative permittivity of metals by a sum of Drude-Lorentz or a sum of partial-fraction models. We use the particle swarm optimization (PSO) hybridized either with Nelder-Mead downhill simplex, or with gradient method. The main electronic transitions in metals help to guide the fitting process toward the solution. The method is automatic and applied blindly to silver, gold, copper, aluminum, chromium, platinum, and titanium.
Physica B: Condensed Matter
Abstract Er3+ doped, Yb3+ doped, and Er3+/Yb3+ co-doped Y2Ti2O7 phosphors with various concentrat... more Abstract Er3+ doped, Yb3+ doped, and Er3+/Yb3+ co-doped Y2Ti2O7 phosphors with various concentrations of Er3+ (12–20%), Yb3+ (1-10 at%), and Er3+Yb3+ (1%, and 1,2,3%, respectively) were prepared by solid-state reaction. The phase structure and purity of all prepared phosphors were studied by X-ray diffraction analysis followed by measurement of the hydrodynamic diameter of each sample by Dynamic light scattering. The formation of the pyrochlore structure was confirmed by the observation of relative vibrations by Fourier Transform Infrared Spectroscopy. Moreover, photoluminescence spectra of different co-doped Y2Ti2O7 compounds are presented to check the energy transfer processes of Er3+ and Yb3+ ions. Finally, phosphors were used for the detection of latent fingermarks on various surfaces and a fingerprint minutia extraction algorithm was used for the analysis of extracted minutiae. The analyses confirm that the co-doped phosphors can be useful for the visualization of latent fingerprints once a good detection of their minutiae is obtained.
Sensors and Actuators B: Chemical, 2017
The luminescence characteristics of GaN films implanted with Erbium at low doses were evaluated. ... more The luminescence characteristics of GaN films implanted with Erbium at low doses were evaluated. The temperature dependence of the YL band allowed us to identify the nitrogenvacancy as the main responsible defect for this emission. The color coordinates analysis indicates that Er 3+ /Yb 3+ co-doped GaN semiconductor emits at room temperature a blended light with color in the white-light region. The significant temperature sensitivity obtained indicates its potential as optical temperature sensing probe in the temperature range 200-300K. The maximum sensitivity reached was 15x10-4 K-1 at 200 K.
ABSTRACT ESBM 2013-CONFERENCE PROGRAM
Journal of Luminescence, 2015
ABSTRACT Abstract In this paper, a new tellurite glass (85TeO2·5.0Nb2O5· 5.0ZnO·5.0LiF) doped wit... more ABSTRACT Abstract In this paper, a new tellurite glass (85TeO2·5.0Nb2O5· 5.0ZnO·5.0LiF) doped with 1 mol% Tm2O3 was prepared by melt-quenching technique. Differential scanning calorimetry (DSC) measurements indicate a good thermal stability, X-ray diffraction patterns show no sign of crystallization. Precise refractive index measurements were performed on five different wavelengths by a prism spectrometer. The optical energy gap, the Sellmeier energy gap and the dispersion energy were estimated. Judd–Ofelt intensity parameters were evaluated in order to obtain electric and magnetic-dipole transition probabilities, branching ratios and radiative lifetimes of several excited states of Tm3+. The classical McCumber theory was used to evaluate the emission cross-sections for the 3F4→3H6 transition at a wavelength of around 1.8 µm. The characteristics of down-conversion luminescence in the visible range were studied by exciting Tm3+ ions into the 1G4 level. Furthermore the structure of this glass was analyzed by Raman spectroscopy.
IEEE Transactions on Nanobioscience, 2017
Engineering Sciences for Biology and Medicine (ESBM) is an exciting platform for researchers to d... more Engineering Sciences for Biology and Medicine (ESBM) is an exciting platform for researchers to discuss a wide range of modern biology and medicine goals. The third edition ESBM 2017 conference was organized by the Tunisian Association of Academic Researchers ATCU, in collaboration with the Technopark of Sfax and the Digital Research Centre of Sfax from May 4–7’ 2017 in Sfax, Tunisia. This conference encourages the scientific interactions among researchers to share their ideas and approaches on all aspects of glitches in biology and medicine. Editors thank all the participants for their contributions, that are greatly appreciated. This special section consists of selected peer-reviewed papers on 1) Nanobiotechnology and Nanomedicine, 2) Systems Biology and Forensics, 3) Health Data & Models, 4) Health Data Processing, 5) Devices, Infrastructure & Communication, and 6) e-Health Services and Applications that highlight current developments. The ESBM 2017 conference received a total of...
IEEE Transactions on NanoBioscience, 2015
Submission Deadline 30/01/2015 Call for papers ESBM 2015 The international conference " Engi... more Submission Deadline 30/01/2015 Call for papers ESBM 2015 The international conference " Engineering Sciences in Biology and Medicine" ESBM'2015 will be organized in Monastir- Tunisia from 01 to 03 Mai 2015. You are invited to submit your abstract by 30 January 2015. Selected high quality research papers will be considered for publication after peer review in a special issue of the following journals: Advanced Science Letters (IF= 1.253) IEEE Transactions on NanoBioscience (IF= 1.768) For more details visit the conference website: http://www.esbm2015.com/
Journal of Photochemistry and Photobiology A Chemistry
New photoluminescent, non-toxic europium doped yttrium titanate phosphors (x mol% Eu3+/Y2Ti2O7 wh... more New photoluminescent, non-toxic europium doped yttrium titanate phosphors (x mol% Eu3+/Y2Ti2O7 where x = 1.0, 2.0, 4.0 6.0, 10, 15 and 30 mol%) with high crystalline structure were synthesized by sol–gel followed by heat treatment at 1000 °C for 5 h. Eu3+/Y2Ti2O7 phosphors were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), FT-IR and photoluminescence (PL) spectroscopy. The effects of heat treatment and europium metal ion concentration on the structure and PL properties were investigated. Eu3+/Y2Ti2O7 phosphors exhibited micro spherical shape with average crystal size from 90 to 144 nm. The PL spectra showed the orange red emission bands of Eu3+ in highly symmetrical host. The longest PL lifetime was detected at 4 mol% Eu3+/Y2Ti2O7 phosphor. The toxicity of 15 mol% Eu3+:Y2Ti2O7 was tested. The obtained result showed LD50 is 3.2 g/kg. The PL and toxicity properties of the prepared phosphors make them promising m...
Journal of Applied Physics, 2015
RSC Adv., 2015
ZnO:Er 3+ ,Yb 3+ thin films with a hexagonal wurtzite structure were successfully deposited on Si... more ZnO:Er 3+ ,Yb 3+ thin films with a hexagonal wurtzite structure were successfully deposited on Si (111) substrates at 430 C by an aerosol-assisted chemical vapor deposition (AACVD) atmospheric pressure process. The films were deposited with fixed 3 mol% erbium concentration and various ytterbium concentrations of 6, 8, 9 and 10 mol%. The annealing treatment at 1000 C was found to enhance the crystallinity and the upconversion (UC) emission of the films. UC emissions were investigated under 980 nm excitation, and the ZnO:Er 3+ ,Yb 3+ films exhibited the intense red 665 nm upconverted emissions of Er 3+ ions originating from an efficient Yb-Er energy transfer process. The absolute upconversion Quantum Yield (UC-QY) of each film was measured for the UC emissions centered at 410, 540 and 665 nm at varying excitation power densities. UC-QY analysis has revealed that the ZnO:3 mol% Er,9 mol% Yb thin film possesses the highest total quantum yield of 5.59 AE 0.1% with a power density of 19.3 AE 3 W cm À2 . These results show that this film is promising as an efficient upconversion layer suitable for many photonic applications.
Journal of Alloys and Compounds
This research work is a detailed study of the effect of deposition conditions on the combined lig... more This research work is a detailed study of the effect of deposition conditions on the combined light trapping and photon conversion properties of Nd 3þ ions doped ZnO nanodisk thin films. Hexagonal wurtzite phased ZnO:Nd films were deposited at the temperature range of [370e500 C] by aerosol assisted chemical vapor deposition (AACVD) process at atmospheric pressure. Actually, annealing treatment at 1000 C in air atmosphere led to the increase of crystallinity, decrease of the porosity of the films and enhancement of their optical properties. Moreover, this work has demonstrated that annealing strongly modifies the local structure and the crystal field of the Nd 3þ ions embedded in ZnO, leading to a high efficiency of visible-to-infrared downconversion (DC) emissions. The optimized 2.805 at.% Nd embedded in ZnO shaped nanodisk thin film exhibits a strong and resolved 920 and 1060 nm DC emissions. In addition, this film presents a low reflectance percentage of 17.1% with average external quantum efficiency (EQE) of 51.0% in the [400e800 nm] range, leading to an improvement of quantum efficiency of 12.5%. These findings show that the combined photon conversion and light trapping properties in semiconducting ZnO:Nd nanodisk shaped thin film is a well known passive approach that can boost c-Si solar cells efficiency.
Nanoscale Research Letters, 2015
We synthesized Gd 2 O 3 and Gd 2 O 3 doped by europium (Eu) (2% to 10%) nanoplatelets using the p... more We synthesized Gd 2 O 3 and Gd 2 O 3 doped by europium (Eu) (2% to 10%) nanoplatelets using the polyol chemical method. The synthesized nanoplatelets were characterized by X-ray diffraction (XRD), FESEM, TEM, and EDX techniques. The optical properties of the synthesized nanoplatelets were investigated by photoluminescence spectroscopy. We also studied the magnetic resonance imaging (MRI) contrast enhancement of T1 relaxivity using 3 T MRI. The XRD for Gd 2 O 3 revealed a cubic crystalline structure. The XRD of Gd 2 O 3 :Eu 3+ nanoplatelets were highly consistent with Gd 2 O 3 indicating the total incorporation of the Eu 3+ ions in the Gd 2 O 3 matrix. The Eu doping of Gd 2 O 3 produced red luminescence around 612 nm corresponding to the radiative transitions from the Eu-excited state 5 D 0 to the 7 F 2 . The photoluminescence was maximal at 5% Eu doping concentration. The stimulated CIE chromaticity coordinates were also calculated. Judd-Ofelt analysis was used to obtain the radiative properties of the sample from the emission spectra. The MRI contrast enhancement due to Gd 2 O 3 was compared to DOTAREM commercial contrast agent at similar concentration of gadolinium oxide and provided similar contrast enhancement. The incorporation of Eu, however, decreased the MRI contrast due to replacement of gadolinium by Eu.