Highly efficient all‐nitride phosphor‐converted white light emitting diode

Mueller‐Mach, Regina; Mueller, Gerd; Krames, Michael R.; Höppe, Henning A.; Stadler, Florian; Schnick, Wolfgang; Juestel, Thomas; Schmidt, Peter J.

doi:10.1002/pssa.200520045

Cited by 584 publications

(477 citation statements)

References 18 publications

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“…This observation indicates to a relatively large covalency of the metal-oxygen bond in Li 2 SrSiO 4 . It is interesting to compare the results with the literature data for lanthanide (Ln¼Ce 3 + , Eu 2 + )-doped alkalineearth silicon nitrides of the composition M 2 Si 5 N 8 (M ¼Ca, Sr), since these materials were found to have a high potential for white LED's applications [25,26]. It is seen that the values of E cfs for Ce 3 + in M 2 Si 5 N 8 (13,000-15,000 cm À 1 [27]) are essentially smaller than that for Li 2 SrSiO 4 :Ce 3 + .…”

Section: What Factors Cause the Long-wavelength Position Of The Eu 2 mentioning

confidence: 95%

Luminescent properties of Eu2+ and Ce3+ ions in strontium litho-silicate Li2SrSiO4

Dotsenko¹,

Levshov²,

Berezovskaya³

et al. 2011

Journal of Luminescence

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a b s t r a c tThe luminescent properties of Eu 2 + and Ce 3 + ions in Li 2 SrSiO 4 have been studied upon excitation in the 2-20 eV region. Based on the results of luminescent measurements, values of the crystal field splitting and the centroid shift of the Ce 3 + 5d configuration in Li 2 SrSiO 4 were found and compared with those of Ce 3 + ions in some other inorganic compounds. The Eu 2 + ions in Li 2 SrSiO 4 exhibit a broad band emission with a maximum at 576 nm, which is due to the 4f 6 5d-4f 7 transition. It was shown that the long-wavelength position of the Eu 2 + emission in Li 2 SrSiO 4 is caused by the large crystal-field splitting of the Eu 2 + 4f 6 5d configuration and relatively high degree of covalency of the Eu-O bond. The stabilization of Eu 2 + ions in Li 2 SrSiO 4 during the synthesis process requires a strong reducing agent. Two phenomenological approaches to explain the low stability of Eu 2 + in Li 2 SrSiO 4 are also discussed.

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Section: What Factors Cause the Long-wavelength Position Of The Eu 2 mentioning

confidence: 95%

Luminescent properties of Eu2+ and Ce3+ ions in strontium litho-silicate Li2SrSiO4

Dotsenko¹,

Levshov²,

Berezovskaya³

et al. 2011

Journal of Luminescence

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“…Recently, the family of alkaline earth nitrido-silicates, M 2 Si 5 N 8 :Eu (M = Ca, Sr, Ba) and their Tm-codoped variants were studied [10]. These materials are much more stable than the aforementioned sulfides and show a high quantum efficiency, which has led to extensive research into their use as conversion phosphors in white LEDs [11,12,[18][19][20][21][22][23][24][25][26][27][28]. Recently, orange and reddish persistent luminescence was reported in these compounds, most notably in Ca 2 Si 5 N 8 :Eu,Tm [10,13,14,18,29,30].…”

Section: Introductionmentioning

confidence: 99%

Temperature and wavelength dependent trap filling in M2Si5N8:Eu (M=Ca, Sr, Ba) persistent phosphors

Smet¹,

Eeckhout²,

Bos³

et al. 2012

Journal of Luminescence

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The evaluation of persistent phosphors is often focused on the processes right after the excitation, namely on the shape of the afterglow decay curve and the duration of the afterglow, in combination with thermoluminescence glow curve analysis. In this paper we study in detail the trap filling process in europium-doped alkaline earth silicon nitrides (Ca 2 Si 5 N 8 :Eu, Sr 2 Si 5 N 8 :Eu and Ba 2 Si 5 N 8 :Eu), i.e., how the persistent luminescence can be induced. Both the temperature at which the phosphors are excited and the spectral distribution of the excitation light on the ability to store energy in the phosphors' lattices are investigated. We show that for these phosphors this storage process is thermally activated upon excitation in the lower 5d excited states of Eu 2+ , with the lowest thermal barrier for europium doped Ca 2 Si 5 N 8 . Also, the influence of co-doping with thulium on the trap filling and afterglow behavior is studied. Finally there exists a clear relation between the luminescence quenching temperature and the trap filling efficiency. The latter relation can be utilized to select new efficient 5d-4f based afterglow phosphors. 2 Center for Nano-and Biophotonics (NB-Photonics), Ghent University, Belgium.

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“…Both metals dissolve under formation of ammonia complexes and electride solutions, so that perfect mixing on the atomic level is achieved. 18 19 Emission derives from transitions between the 5d energy levels and the 4f 8 S 7/2 levels. Different from 4f-4f transitions of Eu 3+ these transitions are parity allowed, therefore strong in intensity, and influenced by the chemical surrounding by inclusion of the Eu 5d levels into the process.…”

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confidence: 99%

Homoleptic imidazolate frameworks 3∞[Sr_1−xEu_x(Im)₂]—hybrid materials with efficient and tuneable luminescence

et al. 2011

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Homoleptic frameworks of the formula 3 N [Sr 1Àx Eu x (Im) 2 ] (1) (x = 0.01-1.0; Im À = imidazolate anion, C 3 H 3 N 2 À ) are hybrid materials that exhibit an intensive green luminescence. Tuning of both emission wavelength and quantum yield is achieved by europium/strontium substitution so that a QE of 80% is reached at a Eu content of 5%. Even 100% pure europium imidazolate still shows 60% absolute quantum efficiency. Substitution of Sr/Eu shows that doping with metal cations can also be utilized for coordination compounds to optimize materials properties. The emission is finely tuneable in the region 495-508 nm via variation of the europium content. The series of frameworks 3 N [Sr 1Àx Eu x (Im) 2 ] presents dense MOFs with the highest quantum yields reported for MOFs so far.Framework and MOF chemistry 1 have attracted attention, as interesting properties were reported like conductivity, 2 catalytic effects, 3 luminescence 4 and porosity. 5 They are mainly known for oxygen coordinating ligands, mostly metal carboxylates 6 which include the alkaline earth and 4f elements. 7 Because of the oxophilicity of lanthanides oxygen-free multi-dimensional coordination networks are rarely found except for a few rare earth imidazolates and triazolates. 8 Among transition metals the imidazole ring system is of exceptional interest together with several 3d metals as they adopt zeolite structures (ZIFs) 9 that can be used for sorption and gas separation. Different from many solid state phosphors, coordination compounds can exhibit luminescence by metal ions although they contain 100% luminescence centres. 10 An expected quenching by concentration is suppressed by ligand shielding. They are furthermore interesting luminescent hybrid materials, as emission can be achieved either via a fluorescence of the ligand system 11 or the metal centres, mainly by the use of lanthanides. 4 The excitation can benefit from antenna effects, viz. the ligand system is excited primarily followed by a transfer of the energy to the luminescence centres. 12 However there are only little coordination compounds for which effective emission characterized by high quantum efficiencies has been reported. 4,11,13 Mostly, no quantum yields were determined, although luminescence becomes important for MOFs concerning sensoring and lighting from UV to near IR. 14,15 We now report a series of homoleptic imidazolate frameworks containing divalent strontium and europium that shows an exceptional combination of properties: an effective luminescence with the highest quantum yield reported for coordination polymers today, together with multiple excitation options including excitation maxima at the applicationally important wavelengths 370 and 460 nm (for Hg and blue LED excitation). The emission can be finely tuned in the region 495-508 nm (blue-green to green) via variation of the Eu content (Fig. 1). Furthermore a low quenching by concentration is observed, combined to a high thermal stability of the frameworks up to 530 1C. (1) are obtained by reactions of t...

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Highly efficient all‐nitride phosphor‐converted white light emitting diode

Cited by 584 publications

References 18 publications

Luminescent properties of Eu2+ and Ce3+ ions in strontium litho-silicate Li2SrSiO4

Luminescent properties of Eu2+ and Ce3+ ions in strontium litho-silicate Li2SrSiO4

Temperature and wavelength dependent trap filling in M2Si5N8:Eu (M=Ca, Sr, Ba) persistent phosphors

Homoleptic imidazolate frameworks 3∞[Sr_1−xEu_x(Im)₂]—hybrid materials with efficient and tuneable luminescence

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Highly efficient all‐nitride phosphor‐converted white light emitting diode

Cited by 584 publications

References 18 publications

Luminescent properties of Eu2+ and Ce3+ ions in strontium litho-silicate Li2SrSiO4

Luminescent properties of Eu2+ and Ce3+ ions in strontium litho-silicate Li2SrSiO4

Temperature and wavelength dependent trap filling in M2Si5N8:Eu (M=Ca, Sr, Ba) persistent phosphors

Homoleptic imidazolate frameworks 3∞[Sr1−xEux(Im)2]—hybrid materials with efficient and tuneable luminescence

Contact Info

Product

Resources

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Homoleptic imidazolate frameworks 3∞[Sr_1−xEu_x(Im)₂]—hybrid materials with efficient and tuneable luminescence