Photoluminescence of Eu2+ in SrGa2S4

Chartier, C.; Barthou, Carlos; Bénalloul, P.; Frigerio, Jean Marc

doi:10.1016/j.jlumin.2004.07.006

Cited by 111 publications

(83 citation statements)

References 25 publications

(42 reference statements)

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“…Clearly, the model of persistent luminescence has to be reconsidered and one should be open to alternative mechanisms and charge carriers. The same applies to the model proposed by Najafov et al 34 and Chartier et al 35 to explain thermal quenching of Eu 2+ 5d-4f emission in SrGa 2 S 4 and CaGa 2 S 4 . The level schemes suggest an alternative mechanism.…”

Section: H108supporting

confidence: 74%

Mechanism of Persistent Luminescence in Eu[sup 2+] and Dy[sup 3+] Codoped Aluminate and Silicate Compounds

Dorenbos

2005

J. Electrochem. Soc.

381

265

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A mechanism of persistent luminescence that was proposed in 1996 for SrAl 2 O 4 :Eu 2+ ;Dy 3+ has been widely adopted to explain afterglow in many Eu 2+ and Dy 3+ codoped aluminates and silicates. The mechanism involves the thermally activated release of a hole from Eu 2+ in its excited 5d state to the valence band which is subsequently trapped by Dy 3+ . In this work the location of the lanthanide energy levels relative to the valence and conduction band of various compounds is presented. It is shown that the mechanism of persistent luminescence cannot be correct. An alternative model that involves the ionization of the 5d electron to conduction band states and subsequent trapping by Dy 3+ is proposed. The level schemes are consistent, both qualitatively and quantitatively, with many observations regarding persistent luminescence. They also provide insight into the mechanism of thermal quenching of Eu 2+ 5d-4f emission. proposed the same mechanism for CaGa 2 S 4 :Eu 2+ . In mechanisms of persistent luminescence, luminescence quenching, and electroluminescence, the thermally activated ionization or field ionization of either electrons to the conduction band or holes to the valence band is an important aspect. To understand these mechanisms it is necessary to accurately know the location of the impurity states relative to the conduction band and the valence band. The problem is that hitherto this information has not been available, leading to mechanisms that rely on speculative ideas.Recently new methods have become available that make it possible to determine the absolute location of the lanthanide impurity levels. In this work we apply these methods to reconsider the mechanism of persistent luminescence and luminescence quenching. It is shown that the mechanism proposed by Matsuzawa et al. Results and DiscussionLevel schemes for CaGa 2 S 4 and SrAl 2 O 4 .-The method to determine the absolute location of the lowest 4f state and the lowest 5d state of divalent and trivalent lanthanide ions in compounds was presented in detail in previous papers and is not repeated here. 36,37Instead only the information used to construct the level schemes in the electroluminescence phosphor CaGa 2 S 4 and the persistent luminescence phosphor SrAl 2 O 4 is presented. Recently Bessiere et al. 38 determined the level scheme for CaGa 2 S 4 . The result is reproduced in Fig. 1 where zero energy is at the top of the valence band. E ex = 4.35 eV is the energy of exciton creation, i.e., a bound electron-hole pair. The energy E VC needed to create a free electron in the conduction band is at 4.9 eV. The lowest 4f and lowest 4f5d levels of the divalent and the trivalent lanthanides are drawn in the scheme as function of the number n in the 4f n state of the trivalent lanthanide. SrGa 2 S 4 has the same crystal structure as CaGa 2 S 4 and also approximately the same bandgap value. We therefore regard the level scheme for CaGa 2 S 4 also as representative for that of SrGa 2 S 4 .Ultraviolet and vacuum ultraviolet ͑VUV͒ studies by Kamada ...

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Section: H108supporting

confidence: 74%

Mechanism of Persistent Luminescence in Eu[sup 2+] and Dy[sup 3+] Codoped Aluminate and Silicate Compounds

Dorenbos

2005

J. Electrochem. Soc.

381

265

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“…Several ternary sulfide compounds have also been proposed as LED phosphor, with especially the thiogallates receiving some attention due to much better stability than for instance the thioaluminates (in casu green-emitting SrGa 2 S 4 :Eu 2+ [37,38,71] choosing the alkaline earth ion (Ca, Sr, Ba) and the dopant ion (Ce, Eu) [144]. A drawback is the relatively low thermal quenching temperature, typically in the 400 to 450K range.…”

Section: Sulfides and Oxysulfidesmentioning

confidence: 99%

Selecting Conversion Phosphors for White Light-Emitting Diodes

Smet

Parmentier

Poelman

2011

J. Electrochem. Soc.

694

501

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Light emitting diodes (LEDs) are on the verge of a breakthrough in general lighting, due to their rapidly improving efficiency. Currently, white LEDs with high color rendering are mainly based on wavelength conversion by one or more phosphor materials. This Review first describes how to quantify the quality of a light source, discussing the color rendering index (CRI) and alternative color quality indices. Then, six main criteria are identified and discussed, which should be fulfilled by a phosphor candidate to be considered for actual application in LEDs. These criteria deal with the shape and position of the emission and the excitation spectra, the thermal quenching behavior, the quantum efficiency, the chemical and thermal stability and finally with the occurrence of saturation effects. Based on these criteria, the most common dopant ions (broad-band emitting Eu AbstractLight emitting diodes (LEDs) are on the verge of a breakthrough in general lighting, due to their rapidly improving efficiency. Currently, white LEDs with high color rendering are mainly based on wavelength conversion by one or more phosphor materials. This Review first describes how to quantify the quality of a light source, discussing the color rendering index (CRI) and alternative color quality indices. Then, six main criteria are identified and discussed, which should be fulfilled by a phosphor candidate to be considered for actual application in LEDs. These criteria deal with the shape and position of the emission and the excitation spectra, the thermal quenching behavior, the quantum efficiency, the chemical and thermal stability and finally with the occurrence of saturation effects. Based on these criteria, the most common dopant ions (broad-band emitting Eu

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“…The value of 0.61 eV obtained in this work for SrGa 2 S 4 :Eu 2+ is close to the value of 0.6 eV that was obtained from bulk measurements by Chartier et al, which is not surprising given the low doping concentration of 0.1% that was used. 29 The proposed microscopic technique allows to extract the thermal quenching energy barrier for an ideally incorporated dopant ion instead of an average value obtained from a bulk measurement, unavoidably having contributions from non-ideal luminescent centers. The optimal E T value is hence well suited for direct comparison with electronic structures determined empirically or from first principles.…”

Section: Results For Srgamentioning

confidence: 99%

Microscopic Study of Dopant Distribution in Europium Doped SrGa₂S₄: Impact on Thermal Quenching and Phosphor Performance

Martin¹,

Poelman²,

Smet³

et al. 2017

ECS J. Solid State Sci. Technol.

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White light emitting diodes start to dominate lighting and display applications. However, the properties of the phosphors used in these devices strongly depend on synthesis conditions. A better understanding of how performance-determining mechanisms such as thermal quenching are influenced by synthesis conditions and sample composition is necessary to achieve the required standards in a goal-oriented strategy. In this paper, a microscopic thermal quenching study on green-emitting SrGa 2 S 4 :Eu 2+ phosphors by means of cathodoluminescence spectroscopy and energy dispersive X-ray analysis in a scanning electron microscope is used to extend our knowledge beyond averaged information obtained on bulk material. Elemental and cathodoluminescence mapping at different temperatures made it possible to determine thermal quenching profiles for sub-micrometer sized areas. These revealed a broad range of local quenching temperatures for samples with ill-distributed dopant ions. For the associated activation energy an upper limit of 0.61 eV was identified, corresponding to the intrinsic thermal quenching of isolated europium ions. Furthermore, the results confirm a previously suggested thermal quenching model which involves the presence of both isolated and clustered dopant ions. Inorganic luminescent materials or phosphors are currently applied on a large scale in various novel technologies. Most notably, white light-emitting diodes (LEDs), which are applied in lighting and display technologies, rely on high-performance phosphors. [1][2][3] Here, the emission of a blue light source, based on a Ga 1-x In x N LED chip is partly absorbed by the phosphor blend that is applied on top of this chip or in a remote fashion. [4][5][6] The phosphor re-emits the absorbed energy as green, yellow and red light, which is mixed with the remaining blue LED emission as to get an overall white emission. This requires subtle fine-tuning, both in terms of material composition, 7,8 as well as device manufacturing 5,9 to achieve white LED devices with the desired properties.From the materials point of view, phosphor properties are highly dependent on synthesis conditions, often in an unpredictable and hardto-control way. This can be attributed to an incomplete understanding of the underlying physical mechanisms for various macroscopic properties. 10 As an example, thermal quenching (TQ), i.e. the decreased internal quantum efficiency of luminescent materials at elevated temperatures, has been attributed to various causes, either intrinsic to the luminescent center itself or due to external influences such as the presence of defects or the local clustering of luminescent ions. 10,11 The undetermined nature of TQ makes it difficult to engineer synthesis routines to yield phosphors with a minimized TQ and an optimized performance.Phosphors are generally studied at the macroscopic level, i.e measurements are typically performed on milligram quantities, a scale which is of relevance for applications. Nonetheless, if materials are inhomogeneous in terms...

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Photoluminescence of Eu2+ in SrGa2S4

Cited by 111 publications

References 25 publications

Mechanism of Persistent Luminescence in Eu[sup 2+] and Dy[sup 3+] Codoped Aluminate and Silicate Compounds

Mechanism of Persistent Luminescence in Eu[sup 2+] and Dy[sup 3+] Codoped Aluminate and Silicate Compounds

Selecting Conversion Phosphors for White Light-Emitting Diodes

Microscopic Study of Dopant Distribution in Europium Doped SrGa₂S₄: Impact on Thermal Quenching and Phosphor Performance

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Photoluminescence of Eu2+ in SrGa2S4

Cited by 111 publications

References 25 publications

Mechanism of Persistent Luminescence in Eu[sup 2+] and Dy[sup 3+] Codoped Aluminate and Silicate Compounds

Mechanism of Persistent Luminescence in Eu[sup 2+] and Dy[sup 3+] Codoped Aluminate and Silicate Compounds

Selecting Conversion Phosphors for White Light-Emitting Diodes

Microscopic Study of Dopant Distribution in Europium Doped SrGa2S4: Impact on Thermal Quenching and Phosphor Performance

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Product

Resources

About

Microscopic Study of Dopant Distribution in Europium Doped SrGa₂S₄: Impact on Thermal Quenching and Phosphor Performance