Some aspects of real structure and thermal decomposition of K2SiF6

Stodolski, Roland; Kolditz, Lothar

doi:10.1016/s0022-1139(00)83308-4

Cited by 17 publications

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“…Nevertheless, a weak endothermic process can be observed between 120 and 250 °C. In agreement with Stodolski and Kolditz, this is ascribed to desorption processes and thermal dissociation of the surface layers, which probably also explains the mass loss of the pristine sample in the TGA experiment. As this might lead to a lowered crystallinity at the powder surface (lowering the quantum efficiency), a protective coating of the phosphor is sometimes applied .…”

Section: Resultssupporting

confidence: 87%

“…By heating in air, a partial transformation to K 3 SiF 7 is observed above 450 °C, as can be seen in the in situ XRPD pattern of commercial K 2 SiF 6 (lower part of Figure ). Following Stodolski and Kolditz, , the onset of this transformation is caused by surface hydrolysis of K 2 SiF 6 between 400 and 500 °C As no SiO 2 was detected in XRPD after heating, it is concluded that the amount of SiO 2 stays below the detection limit or that the SiO 2 is mainly amorphous. In addition to surface hydrolysis, Stodolski and Kolditz mentioned the bulk decomposition of K 2 SiF 6 above 520 °C, also resulting in the formation of K 3 SiF 7 .…”

Section: Resultsmentioning

confidence: 92%

“…Following Stodolski and Kolditz, , the onset of this transformation is caused by surface hydrolysis of K 2 SiF 6 between 400 and 500 °C As no SiO 2 was detected in XRPD after heating, it is concluded that the amount of SiO 2 stays below the detection limit or that the SiO 2 is mainly amorphous. In addition to surface hydrolysis, Stodolski and Kolditz mentioned the bulk decomposition of K 2 SiF 6 above 520 °C, also resulting in the formation of K 3 SiF 7 . The bulk decomposition is accompanied by the release of SiF 4 Considering that the above reactions only occur at temperatures well above LED operating temperatures (which are typically below 200 °C), these effects do not put any constraints on the use of K 2 SiF 6 as a host material in LED phosphors.…”

Section: Resultsmentioning

confidence: 92%

See 2 more Smart Citations

Red Mn⁴⁺-Doped Fluoride Phosphors: Why Purity Matters

Verstraete

Sijbom

Joos

et al. 2018

ACS Appl. Mater. Interfaces

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Traditional light sources, e.g., incandescent and fluorescent lamps, are currently being replaced by white light-emitting diodes (wLEDs) because of their improved efficiency, prolonged lifetime, and environmental friendliness. Much effort has recently been spent to the development of Mn-doped fluoride phosphors that can enhance the color gamut in displays and improve the color rendering index, luminous efficacy of the radiation, and correlated color temperature of wLEDs used for lighting. Purity, stability, and degradation of fluoride phosphors are, however, rarely discussed. Nevertheless, the typical wet chemical synthesis routes (involving hydrogen fluoride (HF)) and the large variety of possible Mn valence states often lead to impurities that drastically influence the performance and stability of these phosphors. In this article, the origins and consequences of impurities formed during synthesis and aging of KSiF:Mn are revealed. Both crystalline impurities such as KHF and ionic impurities such as Mn are found to affect the phosphor performance. While Mn mainly influences the optical absorption behavior, KHF can affect both the optical performance and chemical stability of the phosphor. Moisture leads to decomposition of KHF, forming HF and amorphous hydrated potassium fluoride. As a consequence of hydrate formation, significant amounts of water can be absorbed in impure phosphor powders containing KHF, facilitating the hydrolysis of [MnF] complexes and affecting the optical absorption of the phosphors. Strategies are discussed to identify impurities and to achieve pure and stable phosphors with internal quantum efficiencies of more than 90%.

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Section: Resultssupporting

confidence: 87%

Section: Resultsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 92%

See 1 more Smart Citation

Red Mn⁴⁺-Doped Fluoride Phosphors: Why Purity Matters

Verstraete

Sijbom

Joos

et al. 2018

ACS Appl. Mater. Interfaces

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“…According to [29] the thermal dissociation of K 2 SiF 6 (Eq. 6) is observed at 520°C and with rising of potassium excess, K 3 SiF 7 is formed at lower temperatures.…”

Section: Phase Compositionmentioning

confidence: 99%

Alkali silicate binders: effect of SiO2/Na2O ratio and alkali metal ion type on the structure and mechanical properties

Skorina

Тихомирова

2012

J Mater Sci

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The influence of SiO 2 :Na 2 O molar ratio and the nature of an alkali metal (Na vs. K) in commercial aqueous alkali silicate on the microstructure, textural properties, phase composition, and hydrolytic stability of an alkali silicate binder have been investigated using scanning electron microscopy, nitrogen adsorption/desorption technique, X-ray diffractometry, thermal analysis, and dissolution tests. It has been found that microstructure and textural properties of the alkali silicate binder depend both on silica to alkali molar ratio and type of alkali metal (Na vs. K). Sodium silicate binder obtained from commercial silicate solution with lower SiO 2 :Na 2 O molar ratio (2.2) exhibits a globular microstructure of silica xerogel with high content of micropores, whereas the binder formulated with SiO 2 :Na 2 O molar ratio 3.2 is characterized by more open cluster structure with lower content of micropores. It is observed that surface specific area estimated by Brunauer, Emmett, and Teller method and mesopore volume obtained by the Barrett-Joyner-Halenda method for sodium silicate binder are substantially higher than those for potassium silicate binder. The ultimate hydrolytic stability of the sodium silicate binder increases slightly with increase in the silica to alkali molar ratio within the studied range. Decreasing in SiO 2 :Na 2 O molar ratio and replacement of sodium silicate solution by potassium silicate solution in the corresponding filled composition lead to the improvement of mechanical properties and decrease in open porosity.

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“…The K 3 SiF 7 :Mn 4+ phosphor will open a variety of options for industrial applications because it can mitigate the drawbacks of the K 2 SiF 6 :Mn 4+ phosphor. Although the host, K 3 SiF 7 , has been well known for long periods of time, the Mn 4+ doping and the consequent luminescent and structural properties of the K 3 SiF 7 :Mn 4+ phosphor have never been reported in detail, with the exception of being listed as a possible host for Mn 4+ in a patent with no experimental results . It should be noted that this sort of novel phosphor can be categorized into Type III such as CASN and β‐SIALON phosphors by refereeing to our previous classification principle for LED phosphors …”

Section: Introductionmentioning

confidence: 99%

A novel Mn⁴⁺‐activated red phosphor for use in light emitting diodes, K₃SiF₇:Mn⁴⁺

et al. 2016

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Phosphors that exhibit a narrow red emission are particularly interesting due to the advantage of providing a more extensive color gamut and better rendering in LED applications such as displays and solid‐state lighting. Although some Eu2+‐activated nitridosilicates have been discovered in this regard, K2SiF6:Mn4+ phosphors are the only option in actual LED applications thus far. We discovered a novel phosphor, K3SiF7:Mn4+, with P4/mbm symmetry. The luminescent properties of K3SiF7:Mn4+ are almost identical to those of the K2SiF6:Mn4+ phosphor, but its materials identity is distinct due to a completely different crystallographic structure, which leads to reduced decay time. The fast decay is one of the most serious disadvantages of existing K2SiF6:Mn4+ phosphors. The K3SiF7:Mn4+ phosphor was examined in comparison to the K2SiF6:Mn4+ via density functional theory calculation, Rietveld refinement, X‐ray photoelectron spectroscopy, X‐ray absorption near‐edge structure spectroscopy, and time‐resolved photoluminescence.

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Some aspects of real structure and thermal decomposition of K2SiF6

Cited by 17 publications

References 0 publications

Red Mn⁴⁺-Doped Fluoride Phosphors: Why Purity Matters

Red Mn⁴⁺-Doped Fluoride Phosphors: Why Purity Matters

Alkali silicate binders: effect of SiO2/Na2O ratio and alkali metal ion type on the structure and mechanical properties

A novel Mn⁴⁺‐activated red phosphor for use in light emitting diodes, K₃SiF₇:Mn⁴⁺

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Some aspects of real structure and thermal decomposition of K2SiF6

Cited by 17 publications

References 0 publications

Red Mn4+-Doped Fluoride Phosphors: Why Purity Matters

Red Mn4+-Doped Fluoride Phosphors: Why Purity Matters

Alkali silicate binders: effect of SiO2/Na2O ratio and alkali metal ion type on the structure and mechanical properties

A novel Mn4+‐activated red phosphor for use in light emitting diodes, K3SiF7:Mn4+

Contact Info

Product

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Red Mn⁴⁺-Doped Fluoride Phosphors: Why Purity Matters

Red Mn⁴⁺-Doped Fluoride Phosphors: Why Purity Matters

A novel Mn⁴⁺‐activated red phosphor for use in light emitting diodes, K₃SiF₇:Mn⁴⁺