Anthony Parmentier - Academia.edu (original) (raw)
Papers by Anthony Parmentier
Optical Materials, Sep 1, 2013
Optical Materials, Sep 1, 2012
Due to the lack of efficient green emitting solid state light sources, conversion phosphors emitt... more Due to the lack of efficient green emitting solid state light sources, conversion phosphors emitting saturated green emission are highly interesting, both for display and signalling applications. In this work, we study the luminescence properties of Sr 1Àx Eu x Ga 2 S 4 phosphors over a wide dopant concentration range (x = 0.01-0.3), as function of temperature. The phosphors show a saturated green emission over the entire studied range, with a typical peak wavelength around 536 nm and a FWHM of 50 nm. The internal quantum efficiency is 71% for x = 0.04. For this concentration, the emission intensity at 400 K is still 90% of the intensity at room temperature. By measuring both decay and thermal quenching profiles as a function of europium concentration, we were able to explain the emission properties on the basis of the local environment of the europium ions in the lattice.
Eu 2+ is considered the doping element of choice in colour conversion phosphors for pcLED (phosph... more Eu 2+ is considered the doping element of choice in colour conversion phosphors for pcLED (phosphor converted LED) applications. This is because its 5d-4f transition is highly sensitive to the surrounding host, yielding the interesting possibility to tune the emission wavelength by changing the host material. This characteristic can also be used the other way around: the emission spectrum can be used as a probe for structural investigation.
Alkaline earth thiosilicates are interesting materials for luminescent applications. They can be ... more Alkaline earth thiosilicates are interesting materials for luminescent applications. They can be doped with several rare earth ions, leading to visible light emission (1). Many different phases can be synthesized, often with several different crystallographic sites for the alkaline earth ion (2). Since doping elements such as Eu 2 + and Ce 3+ show an emission spectrum which is strongly dependent on the local environment, they can be used as probes for the alkaline earth site symmetry sites in thiosilicate hosts.
![Research paper thumbnail of Corrigendum to “Luminescence of ytterbium in CaS and SrS” [J. Lumin. 154 (2014) 445–451]](https://attachments.academia-assets.com/111624520/thumbnails/1.jpg)
](Journal of Luminescence, Nov 1, 2014
The authors wish to point out that, in Fig. 6 of their paper on CaS:Yb 2 þ and SrS:Yb 2 þ , the 4... more The authors wish to point out that, in Fig. 6 of their paper on CaS:Yb 2 þ and SrS:Yb 2 þ , the 4f 13 core of the divalent ytterbium ion is systematically written as 2 S 5/2 and 2 S 7/2 , instead of 2 F 5/2 and 2 F 7/2 [1]. Therefore, in this corrigendum the correct figure is provided. The assignments mentioned in the main text are not affected. Contents lists available at ScienceDirect
Optical Materials, Dec 1, 2010
Eu-doped thiosilicate phosphors are promising materials to be used as wavelength convertors in LE... more Eu-doped thiosilicate phosphors are promising materials to be used as wavelength convertors in LEDs. They generally furnish a broad excitation spectrum which overlaps with the emission of many commercially available UV and blue LEDs. Moreover, their emission colour can be tuned from blue to red by changing the alkaline earth metal on the one side (Fig. 1), and by choosing Eu 2+ or Ce 3+ as an activator on the other side. Also, the quantum efficiency of the thiosilicates is acceptable (e.g. 30% for Sr 2 SiS 4 , 35% for Ca 2 SiS 4) and open to further improvement, e.g. by finetuning the synthesis conditions [1]. The thermal quenching temperature T 0.5 (defined as the temperature for which the emission intensity is half of the intensity at low temperature) in Ca 2 SiS 4 :Eu is sufficiently high (470K), but lower for Sr 2 SiS 4 :Eu (380K) [2,3]. From an application point of view, the stability against moisture of the alkaline earth thiosilicates is a matter of concern, but techniques to improve this have been proposed [4]. The luminescent characteristics of the Euions in the thiosilicates are linked to the structural characteristics. This was demonstrated with the study of (Ca,Sr) 2 SiS 4 [3], where the two emission bands of these thiosilicates originate from the two inequivalent sites of the europium ions. Due to the different crystallographic structures of Ca 2 SiS 4 and Sr 2 SiS 4 , phase segregation occurs in Ca 2x Sr 2-2x SiS 4 when 0.5 < x < 0.9. This was observed by x-ray diffraction analysis and cathodoluminescence studies at the microscopic level [3]. Here we also report on the (Ca,Mg) 2 SiS 4system. In the orthorhombic Ca 2 SiS 4-phase, a substitution of a small percentage of Ca 2+ by Mg 2+ shifts the emission spectrum to longer wavelengths. Similarly, in the Mg 2 SiS 4-phase a small percentage of Mg 2+ can be substituted by Ca 2+ , shifting the emission peaks. Intermediate multiphase compositions exhibit more complex PL spectra.
Luminescence quenching when going from Eu-doped alkaline earth thiosilicates to the isocationic t... more Luminescence quenching when going from Eu-doped alkaline earth thiosilicates to the isocationic thiogermanates Europium-doped thiosilicate phosphors M 2 SiS 4 , (M = Ca, Sr, Ba) are promising materials to be used in phosphor-converted LEDs. The efficiency of these phosphors could still be improved by increasing the thermal quenching temperature. This requires a deeper understanding of the position of the 5d and 4f levels of the Eu 2+-ion relative to the bandgap of this class of materials. In pursuit of this understanding, a study of the transition from the M 2 SiS 4 to the isocationic M 2 GeS 4 is performed. These materials are prepared by sintering a mixture of stoichiometric amounts of MS, Si, Ge in a flow of H 2 S. Identification of the resulting materials is done using XRD. The structure of the thiogermanates is found to be very similar to the structure of the thiosilicates, but quite different in luminescent behavior. In contrast with the thiosilicates, the thiogermanates cannot generally be excited efficiently with UV light at room temperature. (In agreement with the results of Olivier-Fourcade, Mat. Res. Bull. Vol. 10, 975-982) Diffuse reflectance spectra of the thiosilicates and the thiogermanates are recorded and linked with the PL measurements.
The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spec... more The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spectra are presented and related to an energy level scheme. A comparison with divalent europium in the same host is carried out.
Journal of Luminescence, Oct 1, 2014
The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spec... more The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spectra are presented and related to an energy level scheme. A comparison with divalent europium in the same host is carried out.
Alkaline earth thiosilicates are interesting materials for luminescent applications. They can be ... more Alkaline earth thiosilicates are interesting materials for luminescent applications. They can be doped with several rare earth ions, leading to visible light emission (1). Many different phases can be synthesized, often with several different crystallographic sites for the alkaline earth ion (2). Since doping elements such as Eu 2 + and Ce 3+ show an emission spectrum which is strongly dependent on the local environment, they can be used as probes for the alkaline earth site symmetry sites in thiosilicate hosts. In strontiumthiodisilicate (SrSi 2 S 5), in contrast to many other thiosilicates, there is only one site to be occupied by a luminescent ion, such as cerium or europium. As a result, we can use the excitation spectra of cerium in this host to extract information on the coordination and local symmetry of this site. Two different crystallographic models can be found in literature, one cubic model (Ribes (3) analogous to BaGe 2 S 5) and one monoclinic model (Nakamura (4), space group C 2). Therefore, we compare both models and we investigate if both models are in accordance with the x-ray diffraction measurements and with the luminescence properties. The typical spin-orbit split cerium emission of 465 nm and 515 nm is discussed. References (1) P.
Journal of Luminescence, 2014
The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spec... more The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spectra are presented and related to an energy level scheme. A comparison with divalent europium in the same host is carried out.
![Research paper thumbnail of Corrigendum to “Luminescence of ytterbium in CaS and SrS” [J. Lumin. 154 (2014) 445–451]](https://attachments.academia-assets.com/98096073/thumbnails/1.jpg)
](Journal of Luminescence, 2014
The authors wish to point out that, in Fig. 6 of their paper on CaS:Yb 2 þ and SrS:Yb 2 þ , the 4... more The authors wish to point out that, in Fig. 6 of their paper on CaS:Yb 2 þ and SrS:Yb 2 þ , the 4f 13 core of the divalent ytterbium ion is systematically written as 2 S 5/2 and 2 S 7/2 , instead of 2 F 5/2 and 2 F 7/2 [1]. Therefore, in this corrigendum the correct figure is provided. The assignments mentioned in the main text are not affected. Contents lists available at ScienceDirect
Physical Chemistry Chemical Physics, 2013
Due to its bright yellow-to-red emission, europium doped Ca2SiS4 is a very interesting material f... more Due to its bright yellow-to-red emission, europium doped Ca2SiS4 is a very interesting material for phosphor converted light emitting diodes. The emission spectrum is highly dependent on the Eu concentration and can consist of more than one emission band. We combined X-ray absorption fine structure and photoluminescence measurements to analyze the structure of europium centers in (Ca,Eu)2SiS4 luminescent powders. This paper provides an explanation for the concentration dependency of the emission spectra. We find that at low dopant concentrations a large fraction of trivalent europium ions is unexpectedly present in the powders. These trivalent europium ions tend to form defect clusters in the luminescent powders. Furthermore we observe a preferential substitution of the europium ions over the two different substitutional Ca sites, which changes upon increasing the dopant concentration. At high dopant concentration, the powder crystallizes in the monoclinic Eu2SiS4 structure. Once more a preferential substitution of the europium ions is observed. Summarizing, the influence of the concentration on the emission spectrum is explained by a difference in preferential occupation of the Eu ions in the lattice.
Optical Materials, 2010
Divalent europium is notorious for the tunability of its emission, depending on the host material... more Divalent europium is notorious for the tunability of its emission, depending on the host material in which it is used as a dopant. In europium-doped alkaline earth thiosilicates, two distinct emission bands can be observed for the alkaline earth metals Mg, Ca and Sr while only a single band is found for barium thiosilicate. In this work, we first complete the data with europiumdoped magnesiumthiosilicate. Then, the solid solution of calcium and magnesium thiosilicate is presented. To conclude, the presence of multiple emission peaks in some compounds is explained on a structural basis, by analysing the possibilities for preferential orientation of the europium d-orbitals.
Optical Materials, 2012
ABSTRACT Due to the lack of efficient green emitting solid state light sources, conversion phosph... more ABSTRACT Due to the lack of efficient green emitting solid state light sources, conversion phosphors emitting saturated green emission are highly interesting, both for display and signalling applications. In this work, we study the luminescence properties of Sr1−xEuxGa2S4 phosphors over a wide dopant concentration range (x = 0.01–0.3), as function of temperature. The phosphors show a saturated green emission over the entire studied range, with a typical peak wavelength around 536 nm and a FWHM of 50 nm. The internal quantum efficiency is 71% for x = 0.04. For this concentration, the emission intensity at 400 K is still 90% of the intensity at room temperature. By measuring both decay and thermal quenching profiles as a function of europium concentration, we were able to explain the emission properties on the basis of the local environment of the europium ions in the lattice.
Materials, 2013
Sr 2 SiS 4 :Ce 3+ is an efficient blue-emitting (460 nm) phosphor, excitable with light of wavele... more Sr 2 SiS 4 :Ce 3+ is an efficient blue-emitting (460 nm) phosphor, excitable with light of wavelengths up to 420 nm. From the excitation spectrum, we construct the energy level scheme and use it to check the predictive power of the Dorenbos model, relating the positions of the Ce 3+ energy levels with those of Eu 2+ in the same host. For strontium thiosilicate, this method gives excellent results and allows us to determine which of two available crystallographic sites is occupied by cerium. We use the Dorenbos method for extracting information on the coordination of Ce 3+ from the observed crystal field splitting.
Journal of Physics D: Applied Physics, 2010
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Optical Materials, Sep 1, 2013
Optical Materials, Sep 1, 2012
Due to the lack of efficient green emitting solid state light sources, conversion phosphors emitt... more Due to the lack of efficient green emitting solid state light sources, conversion phosphors emitting saturated green emission are highly interesting, both for display and signalling applications. In this work, we study the luminescence properties of Sr 1Àx Eu x Ga 2 S 4 phosphors over a wide dopant concentration range (x = 0.01-0.3), as function of temperature. The phosphors show a saturated green emission over the entire studied range, with a typical peak wavelength around 536 nm and a FWHM of 50 nm. The internal quantum efficiency is 71% for x = 0.04. For this concentration, the emission intensity at 400 K is still 90% of the intensity at room temperature. By measuring both decay and thermal quenching profiles as a function of europium concentration, we were able to explain the emission properties on the basis of the local environment of the europium ions in the lattice.
Eu 2+ is considered the doping element of choice in colour conversion phosphors for pcLED (phosph... more Eu 2+ is considered the doping element of choice in colour conversion phosphors for pcLED (phosphor converted LED) applications. This is because its 5d-4f transition is highly sensitive to the surrounding host, yielding the interesting possibility to tune the emission wavelength by changing the host material. This characteristic can also be used the other way around: the emission spectrum can be used as a probe for structural investigation.
Alkaline earth thiosilicates are interesting materials for luminescent applications. They can be ... more Alkaline earth thiosilicates are interesting materials for luminescent applications. They can be doped with several rare earth ions, leading to visible light emission (1). Many different phases can be synthesized, often with several different crystallographic sites for the alkaline earth ion (2). Since doping elements such as Eu 2 + and Ce 3+ show an emission spectrum which is strongly dependent on the local environment, they can be used as probes for the alkaline earth site symmetry sites in thiosilicate hosts.
Journal of Luminescence, Nov 1, 2014
The authors wish to point out that, in Fig. 6 of their paper on CaS:Yb 2 þ and SrS:Yb 2 þ , the 4... more The authors wish to point out that, in Fig. 6 of their paper on CaS:Yb 2 þ and SrS:Yb 2 þ , the 4f 13 core of the divalent ytterbium ion is systematically written as 2 S 5/2 and 2 S 7/2 , instead of 2 F 5/2 and 2 F 7/2 [1]. Therefore, in this corrigendum the correct figure is provided. The assignments mentioned in the main text are not affected. Contents lists available at ScienceDirect
Optical Materials, Dec 1, 2010
Eu-doped thiosilicate phosphors are promising materials to be used as wavelength convertors in LE... more Eu-doped thiosilicate phosphors are promising materials to be used as wavelength convertors in LEDs. They generally furnish a broad excitation spectrum which overlaps with the emission of many commercially available UV and blue LEDs. Moreover, their emission colour can be tuned from blue to red by changing the alkaline earth metal on the one side (Fig. 1), and by choosing Eu 2+ or Ce 3+ as an activator on the other side. Also, the quantum efficiency of the thiosilicates is acceptable (e.g. 30% for Sr 2 SiS 4 , 35% for Ca 2 SiS 4) and open to further improvement, e.g. by finetuning the synthesis conditions [1]. The thermal quenching temperature T 0.5 (defined as the temperature for which the emission intensity is half of the intensity at low temperature) in Ca 2 SiS 4 :Eu is sufficiently high (470K), but lower for Sr 2 SiS 4 :Eu (380K) [2,3]. From an application point of view, the stability against moisture of the alkaline earth thiosilicates is a matter of concern, but techniques to improve this have been proposed [4]. The luminescent characteristics of the Euions in the thiosilicates are linked to the structural characteristics. This was demonstrated with the study of (Ca,Sr) 2 SiS 4 [3], where the two emission bands of these thiosilicates originate from the two inequivalent sites of the europium ions. Due to the different crystallographic structures of Ca 2 SiS 4 and Sr 2 SiS 4 , phase segregation occurs in Ca 2x Sr 2-2x SiS 4 when 0.5 < x < 0.9. This was observed by x-ray diffraction analysis and cathodoluminescence studies at the microscopic level [3]. Here we also report on the (Ca,Mg) 2 SiS 4system. In the orthorhombic Ca 2 SiS 4-phase, a substitution of a small percentage of Ca 2+ by Mg 2+ shifts the emission spectrum to longer wavelengths. Similarly, in the Mg 2 SiS 4-phase a small percentage of Mg 2+ can be substituted by Ca 2+ , shifting the emission peaks. Intermediate multiphase compositions exhibit more complex PL spectra.
Luminescence quenching when going from Eu-doped alkaline earth thiosilicates to the isocationic t... more Luminescence quenching when going from Eu-doped alkaline earth thiosilicates to the isocationic thiogermanates Europium-doped thiosilicate phosphors M 2 SiS 4 , (M = Ca, Sr, Ba) are promising materials to be used in phosphor-converted LEDs. The efficiency of these phosphors could still be improved by increasing the thermal quenching temperature. This requires a deeper understanding of the position of the 5d and 4f levels of the Eu 2+-ion relative to the bandgap of this class of materials. In pursuit of this understanding, a study of the transition from the M 2 SiS 4 to the isocationic M 2 GeS 4 is performed. These materials are prepared by sintering a mixture of stoichiometric amounts of MS, Si, Ge in a flow of H 2 S. Identification of the resulting materials is done using XRD. The structure of the thiogermanates is found to be very similar to the structure of the thiosilicates, but quite different in luminescent behavior. In contrast with the thiosilicates, the thiogermanates cannot generally be excited efficiently with UV light at room temperature. (In agreement with the results of Olivier-Fourcade, Mat. Res. Bull. Vol. 10, 975-982) Diffuse reflectance spectra of the thiosilicates and the thiogermanates are recorded and linked with the PL measurements.
The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spec... more The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spectra are presented and related to an energy level scheme. A comparison with divalent europium in the same host is carried out.
Journal of Luminescence, Oct 1, 2014
The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spec... more The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spectra are presented and related to an energy level scheme. A comparison with divalent europium in the same host is carried out.
Alkaline earth thiosilicates are interesting materials for luminescent applications. They can be ... more Alkaline earth thiosilicates are interesting materials for luminescent applications. They can be doped with several rare earth ions, leading to visible light emission (1). Many different phases can be synthesized, often with several different crystallographic sites for the alkaline earth ion (2). Since doping elements such as Eu 2 + and Ce 3+ show an emission spectrum which is strongly dependent on the local environment, they can be used as probes for the alkaline earth site symmetry sites in thiosilicate hosts. In strontiumthiodisilicate (SrSi 2 S 5), in contrast to many other thiosilicates, there is only one site to be occupied by a luminescent ion, such as cerium or europium. As a result, we can use the excitation spectra of cerium in this host to extract information on the coordination and local symmetry of this site. Two different crystallographic models can be found in literature, one cubic model (Ribes (3) analogous to BaGe 2 S 5) and one monoclinic model (Nakamura (4), space group C 2). Therefore, we compare both models and we investigate if both models are in accordance with the x-ray diffraction measurements and with the luminescence properties. The typical spin-orbit split cerium emission of 465 nm and 515 nm is discussed. References (1) P.
Journal of Luminescence, 2014
The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spec... more The luminescence of ytterbium doped calcium thiosilicate is studied. Excitation and emission spectra are presented and related to an energy level scheme. A comparison with divalent europium in the same host is carried out.
Journal of Luminescence, 2014
The authors wish to point out that, in Fig. 6 of their paper on CaS:Yb 2 þ and SrS:Yb 2 þ , the 4... more The authors wish to point out that, in Fig. 6 of their paper on CaS:Yb 2 þ and SrS:Yb 2 þ , the 4f 13 core of the divalent ytterbium ion is systematically written as 2 S 5/2 and 2 S 7/2 , instead of 2 F 5/2 and 2 F 7/2 [1]. Therefore, in this corrigendum the correct figure is provided. The assignments mentioned in the main text are not affected. Contents lists available at ScienceDirect
Physical Chemistry Chemical Physics, 2013
Due to its bright yellow-to-red emission, europium doped Ca2SiS4 is a very interesting material f... more Due to its bright yellow-to-red emission, europium doped Ca2SiS4 is a very interesting material for phosphor converted light emitting diodes. The emission spectrum is highly dependent on the Eu concentration and can consist of more than one emission band. We combined X-ray absorption fine structure and photoluminescence measurements to analyze the structure of europium centers in (Ca,Eu)2SiS4 luminescent powders. This paper provides an explanation for the concentration dependency of the emission spectra. We find that at low dopant concentrations a large fraction of trivalent europium ions is unexpectedly present in the powders. These trivalent europium ions tend to form defect clusters in the luminescent powders. Furthermore we observe a preferential substitution of the europium ions over the two different substitutional Ca sites, which changes upon increasing the dopant concentration. At high dopant concentration, the powder crystallizes in the monoclinic Eu2SiS4 structure. Once more a preferential substitution of the europium ions is observed. Summarizing, the influence of the concentration on the emission spectrum is explained by a difference in preferential occupation of the Eu ions in the lattice.
Optical Materials, 2010
Divalent europium is notorious for the tunability of its emission, depending on the host material... more Divalent europium is notorious for the tunability of its emission, depending on the host material in which it is used as a dopant. In europium-doped alkaline earth thiosilicates, two distinct emission bands can be observed for the alkaline earth metals Mg, Ca and Sr while only a single band is found for barium thiosilicate. In this work, we first complete the data with europiumdoped magnesiumthiosilicate. Then, the solid solution of calcium and magnesium thiosilicate is presented. To conclude, the presence of multiple emission peaks in some compounds is explained on a structural basis, by analysing the possibilities for preferential orientation of the europium d-orbitals.
Optical Materials, 2012
ABSTRACT Due to the lack of efficient green emitting solid state light sources, conversion phosph... more ABSTRACT Due to the lack of efficient green emitting solid state light sources, conversion phosphors emitting saturated green emission are highly interesting, both for display and signalling applications. In this work, we study the luminescence properties of Sr1−xEuxGa2S4 phosphors over a wide dopant concentration range (x = 0.01–0.3), as function of temperature. The phosphors show a saturated green emission over the entire studied range, with a typical peak wavelength around 536 nm and a FWHM of 50 nm. The internal quantum efficiency is 71% for x = 0.04. For this concentration, the emission intensity at 400 K is still 90% of the intensity at room temperature. By measuring both decay and thermal quenching profiles as a function of europium concentration, we were able to explain the emission properties on the basis of the local environment of the europium ions in the lattice.
Materials, 2013
Sr 2 SiS 4 :Ce 3+ is an efficient blue-emitting (460 nm) phosphor, excitable with light of wavele... more Sr 2 SiS 4 :Ce 3+ is an efficient blue-emitting (460 nm) phosphor, excitable with light of wavelengths up to 420 nm. From the excitation spectrum, we construct the energy level scheme and use it to check the predictive power of the Dorenbos model, relating the positions of the Ce 3+ energy levels with those of Eu 2+ in the same host. For strontium thiosilicate, this method gives excellent results and allows us to determine which of two available crystallographic sites is occupied by cerium. We use the Dorenbos method for extracting information on the coordination of Ce 3+ from the observed crystal field splitting.
Journal of Physics D: Applied Physics, 2010
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.