Luminescent Materials

Blasse, G.; Grabmaier, B. C.

doi:10.1007/978-3-642-79017-1

Cited by 4,100 publications

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“…On the other hand, the lowest multiplet term 3 F of the free Ni +2 ion in split into 1 T 2g ( 1 D), 3 T 2g ( 3 F) and 3 A 2g ( 3 F) through the anisotropic hybridization [29,30]. Three luminescence bands in the near IR, red and green parts of the spectrum characterize Ni +2 in many synthetic luminofors [31]. For example, a broad IR band peaking at 1520 nm and connected with electron transition from the lowest excited state 3 T 2g has been found in enstatite artificially activated by Ni +2 [32].…”

Section: Resultsmentioning

confidence: 99%

Tuning luminescence of 3d transition- metal doped quantum particles: Ni+2: CdS and Fe+3: CdS

Taheri¹,

Yousefi²,

Khosravi³

2010

Braz. J. Phys.

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The room-temperature photoluminescence of Cd 1−x M x S (M=Ni, Fe) nanoparticles were investigated. Compared with the photoluminescence of CdS which peaks at 475 nm, the photoemission of CdS:Fe nanoparticles was peaking at 537 nm because of Fe acting as luminescent centers. On the other hand, the green emission (503 nm) of CdS:Ni attributed to the 1 T 2g (D)→ 3 A 2g (F) raditive transition. With the increase of the Ni +2 concentration, photoluminescence intensity is increased while by Fe replacement with Cd ions, PL intensity is decreased. Relative to bulk crystals, due to the quantum confinement effect the band gap of CdS clusters is significantly blue-shifted with decreasing cluster size. CdS nanoclusters present a mixed hexagonal/cubic structure and with increasing doping concentration the peaks position of doped CdS shifts to higher angle.

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Section: Resultsmentioning

confidence: 99%

Tuning luminescence of 3d transition- metal doped quantum particles: Ni+2: CdS and Fe+3: CdS

Taheri¹,

Yousefi²,

Khosravi³

2010

Braz. J. Phys.

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“…The applications of lanthanide ions in the field of optical materials is related to the unique energy level diagrams of the lanthanides which are known as the Dieke diagram. The rich energy level structure make that lanthanide ions are perfect ''photon managers'' that can be used to efficiently convert radiation into light of any desired wavelength [1]. In the past four decades the use of lanthanide ions as photon managers has rapidly increased.…”

Section: Introductionmentioning

confidence: 99%

Photon management with lanthanides

et al. 2006

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Efficient conversion of photons from high energy radiation (e.g. ultraviolet or X-rays) to lower energies (visible) has been optimized by using luminescent materials based on the optical properties of lanthanide ions. Presently, luminescent materials with efficiencies close to the theoretical maximum are applied in e.g. fluorescent tubes, X-ray imaging and color television. Contrary to the mature status of luminescent materials in these fields, areas requiring new luminescent materials are emerging. There is great challenge in research on upand downconversion materials and lanthanide ions are the prime candidates to achieve efficient materials. Here downconversion processes will be discussed for VUV phosphors with Pr 3+ . The efficiency of resonant energy transfer of the 1 S 0 -1 I 6 energy from Pr 3+ to Eu 3+ and Mn 2+ is investigated. The aim is to convert the 405 nm photon of the first step of the well-known cascade emission of Pr 3+ into a more useful visible photon. For co-doping with Eu 3+ it is observed that the Pr 3+ emission is quenched, most probably through a metal-to-metal charge-transfer state. The energy transfer from Pr 3+ to Mn 2+ is found to be inefficient.An alternative for downconversion through resonant energy transfer is the non-resonant process of cooperative sensitization. For the Tb-Yb couple efficient cooperative energy transfer from the 5 D 4 level of Tb 3+ to two Yb 3+ neighbors is observed with a transfer rate of 0.26 ms À1 . This corresponds to an upper limit of 188% for the conversion efficiency of visible (490 nm) photons to infrared ($1000 nm) photons.

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“…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. 20 For imidazolate this results in an emission of 1 in the green region. Participation of Eu 3+ in the emission can be excluded as the typical line emission 5 D 4 to the 7 F J states is not observed.…”

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confidence: 99%

“…Participation of Eu 3+ in the emission can be excluded as the typical line emission 5 D 4 to the 7 F J states is not observed. 20 The emission maximum can be finely tuned by the content of europium over 14 nm and range from 495 nm for 1% Eu to 508 nm for 100% Eu and results in a pronounced shift of the colour points and thereby of the emission colour from blue green to bright green according to CIE (Commission Internationale de l'Eclairage). 21 Most efficient emission is observed for Sr : Eu = 95 : 5 with a quantum yield of about 80% (l exc = 366 nm, see Table 1 6 polyhedron is edge connected to two other polyhedra.…”

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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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Luminescent Materials

Cited by 4,100 publications

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Tuning luminescence of 3d transition- metal doped quantum particles: Ni+2: CdS and Fe+3: CdS

Tuning luminescence of 3d transition- metal doped quantum particles: Ni+2: CdS and Fe+3: CdS

Photon management with lanthanides

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

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Luminescent Materials

Cited by 4,100 publications

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Tuning luminescence of 3d transition- metal doped quantum particles: Ni+2: CdS and Fe+3: CdS

Tuning luminescence of 3d transition- metal doped quantum particles: Ni+2: CdS and Fe+3: CdS

Photon management with lanthanides

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

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Product

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