“… 14 , 15 For instance, red-emissive K 2 SiF 6 :Mn 4+ (octahedral coordination) has become a commercial red phosphor for white light-emitting diodes. 16 In a tetrahedral field ( T d ) of oxide ligands, 17 , 18 green emission of Mn(II) is characterized by a fwhm below 45 nm and can be as narrow as 26 nm. 18 However, the main drawback of the oxide field is slow emission decay, typically 4–6 ms.…”
Finding narrow-band light emitters for the visible spectral
region
remains an immense challenge. Such phosphors are in great demand for
solid-state lighting and display application. In this context, green
luminescence from tetrahedrally coordinated Mn(II) is an attractive
research direction. While the oxide–ligand environment had
been studied for decades, much less systematic efforts have been undertaken
with regard to halide coordination, especially in the form of fully
inorganic halide matrixes. In this study, we synthesized a series
of hybrid organic–inorganic Mn(II) halides as well as a range
of fully inorganic Zn halide hosts (chlorides, bromides, iodides)
doped with Mn(II). In the latter, tetrahedral coordination is attained
via substitutional doping owing to the tetrahedral symmetry of Zn
sites. We find that the choice of the halide as well as subtle details
of the crystal structure profoundly govern the photoluminescence peak
positions (500–550 nm range) and emission line widths (40–60
nm) as well as radiative lifetimes (shorter for iodides) through the
altered ligand-field effects and degrees of spin–orbit coupling.
The photoluminescence quantum yields were as high as 70–90%.
The major hurdle for the practical use of these compounds lies in
their low absorption coefficients in the blue spectral regions.
“… 14 , 15 For instance, red-emissive K 2 SiF 6 :Mn 4+ (octahedral coordination) has become a commercial red phosphor for white light-emitting diodes. 16 In a tetrahedral field ( T d ) of oxide ligands, 17 , 18 green emission of Mn(II) is characterized by a fwhm below 45 nm and can be as narrow as 26 nm. 18 However, the main drawback of the oxide field is slow emission decay, typically 4–6 ms.…”
Finding narrow-band light emitters for the visible spectral
region
remains an immense challenge. Such phosphors are in great demand for
solid-state lighting and display application. In this context, green
luminescence from tetrahedrally coordinated Mn(II) is an attractive
research direction. While the oxide–ligand environment had
been studied for decades, much less systematic efforts have been undertaken
with regard to halide coordination, especially in the form of fully
inorganic halide matrixes. In this study, we synthesized a series
of hybrid organic–inorganic Mn(II) halides as well as a range
of fully inorganic Zn halide hosts (chlorides, bromides, iodides)
doped with Mn(II). In the latter, tetrahedral coordination is attained
via substitutional doping owing to the tetrahedral symmetry of Zn
sites. We find that the choice of the halide as well as subtle details
of the crystal structure profoundly govern the photoluminescence peak
positions (500–550 nm range) and emission line widths (40–60
nm) as well as radiative lifetimes (shorter for iodides) through the
altered ligand-field effects and degrees of spin–orbit coupling.
The photoluminescence quantum yields were as high as 70–90%.
The major hurdle for the practical use of these compounds lies in
their low absorption coefficients in the blue spectral regions.
“…Determining the Mn 4+ concentration is crucial, as often only a fraction of the Mn 4+ ions is incorporated during the synthesis 19,34 . Reports that do perform elemental analysis study only a small range of Mn 4+ doping concentrations and do not provide insight into the role of concentration quenching in Mn 4+ doped fluorides 13,35,36 . An in-depth investigation of concentration quenching in Mn 4+ -doped fluorides is thus lacking, despite it being very important for the application of Mn 4+ -doped fluorides in w-LEDs.Fig.…”
Red-emitting Mn4+-doped fluorides are a promising class of materials to improve the color rendering and luminous efficacy of white light-emitting diodes (w-LEDs). For w-LEDs, the luminescence quenching temperature is very important, but surprisingly no systematic research has been conducted to understand the mechanism for thermal quenching in Mn4+-doped fluorides. Furthermore, concentration quenching of the Mn4+ luminescence can be an issue but detailed investigations are lacking. In this work, we study thermal quenching and concentration quenching in Mn4+-doped fluorides by measuring luminescence spectra and decay curves of K2TiF6:Mn4+ between 4 and 600 K and for Mn4+ concentrations from 0.01% to 15.7%. Temperature-dependent measurements on K2TiF6:Mn4+ and other Mn4+-doped phosphors show that quenching occurs through thermally activated crossover between the 4T2 excited state and 4A2 ground state. The quenching temperature can be optimized by designing host lattices in which Mn4+ has a high 4T2 state energy. Concentration-dependent studies reveal that concentration quenching effects are limited in K2TiF6:Mn4+ up to 5% Mn4+. This is important, as high Mn4+ concentrations are required for sufficient absorption of blue LED light in the parity-forbidden Mn4+
d–d transitions. At even higher Mn4+ concentrations (>10%), the quantum efficiency decreases, mostly due to direct energy transfer to quenching sites (defects and impurity ions). Optimization of the synthesis to reduce quenchers is crucial for developing more efficient highly absorbing Mn4+ phosphors. The present systematic study provides detailed insights into temperature and concentration quenching of Mn4+ emission and can be used to realize superior narrow-band red Mn4+ phosphors for w-LEDs.
“…The thermal decomposition of fluosilicates of alkaline and earth alkaline metals happen in the range of 300-700 °C. It was mentioned before that 1 mole of sodium fluosilicate (Na2SiF6) would be decomposed to 2 moles of sodium fluoride and 1 mole of silicon tetrafluoride as decomposition products by heating (Yeo et al, 2016). Sodium fluoride (NaF) is a stable salt which remains after reaction as a solid product.…”
Section: Methodsmentioning
confidence: 99%
“…Recently it was reported the usage of SSF powder in some advanced applications such as cryolite production, coated papers, foam production, filler for bonded abrasives, rubber tires and acid clay manufacturing. As an important fluorosilicate chemical, sodium fluorosilicate has also received considerable attention high-tech products and synthesis over the past decades (Yeo et al, 2016). It was widely used as a versatile template to synthesize NbSi2 films, Si3N4 fibers, Si nanowires, red phosphors and Pt nanotubes (Arai et al, 2011;Jeong et al, 2010).…”
ÖzSodyum silikoflorür, Na2SiF6'nın kimyasal formülü ile son zamanlarda seramik, metalurji ve kimya mühendisliği gibi çeşitli endüstrilerde birçok uygulama alanı bulan inorganik sentetik bir malzemedir. Bu tozun en önemli kullanımlarından bazıları opal cam-seramik, sırlar ve fritlerdir. Uygulama alanlarının gün geçtikçe artmasına karşı, literatürde sodium silikoflorür (SSF) ile ilgili sınırlı sayıda kaynak mevcuttur. Bu araştırmada, ticari bir sodyum silikoflorür tozunun ısıl davranış ve mikroyapı açısından karakterize edilmiştir. Termal analiz, hava atmosferinde 900 °C'de diferansiyel termal ve termo gravimetri eğrilerine göre araştırılmıştır. Mikroyapısal analizler, taneciklerin tane büyüklüğü ve morfolojisini incelemek için taramalı ve geçirimli elektron mikroskopları kullanılarak yapılmıştır. Sonuçlar, ticari sodyum silikoflorür malzemesinin, eşlik eden bir endotermik reaksiyonla havada 430-600 °C sıcaklık aralığında çözündüğünü göstermiştir. Mikroyapısal karakterizasyonlarla, incelenen SSF tozunun granüler morfolojisi, altıgen şekilli prizmaların ve ilgili gözeneklerin varlığına da açıklık getirmiştir.Anahtar Kelimeler "Sodyum silicoflorür, Karakterizasyon, Termal analiz, Elektron mikroskobu." Abstract Sodium silicofluoride, with the chemical formula of Na2SiF6, is an inorganic synthetic material which recently found lots of applications in various industries such as ceramic, metallurgy and chemical engineering. One of the main important usages of this powder is in the production of opal glass-ceramics, glazes and frits. Despite the expansion of its applications, the properties of this material were not investigated deeply elsewhere. In this research, a commercial sodium silicofluoride powder was studied and characterized in terms of thermal behavior and microstructure. The thermal analysis was investigated according to the differential thermal and thermo gravimetry curves by heating the material up to 900 °C in air. The microstructural analyses were also performed using scanning and transmission electron microscopies to study the grain size and morphology of the particles. The results showed that this commercial sodium silicofluoride material is decomposed in the temperature range of 430-600 °C in air by an accompanied endothermic reaction. The microstructural characterizations were also clarified the granular morphology of the studied SSF powder, existence of the hexagonal shaped prisms and associated pores.
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