Nitridosilicates and Oxonitridosilicates: From Ceramic Materials to Structural and Functional Diversity

Electronic, optical and mechanical properties of SrSi6N8 and SrSi6N8O via first-principles

The different properties of two structurally similar nitridosilicates, SrSi₆N₈ and SrSi₆N₈O, are attributed to the oxygen atom.

Structural phase transitions and photoluminescence properties of oxonitridosilicate phosphors under high hydrostatic pressure

Spectroscopic properties of a series of (Sr_0.98-xBa_xEu_0.02)Si₂O₂N₂ (0 ≤ x ≤ 0.98) compounds has been studied under high hydrostatic pressure applied in a diamond anvil cell up to 200 kbar. At ambient pressure the crystal structures of (Sr_0.98-xBa_xEu_0.02)Si₂O₂N₂ (0 ≤ x ≤ 0.98) are related to the ratio of strontium to barium and three different phases exists: orthorhombic Pbcn(0.78 ≤ x ≤ 0.98), triclinic P1 (0 < x ≤ 0.65) and triclinic P1 (0.65 < x < 0.78). It was found that Eu²⁺ luminescence reveals abrupt changes under pressure (decay time, energy and shape) which indicate the variation of the local symmetry and crystal field strength in Eu²⁺ sites. These changes are attributed to the reversible pressure-induced structural phase transitions of triclinic (Sr_0.98-xBa_xEu_0.02)Si₂O₂N₂ into orthorhombic structure. Pressure in which phase transition occurs decreases linearly with increasing of Ba composition in (Sr_0.98-xBa_xEu_0.02)Si₂O₂N₂ series. Additionally, very different pressure shifts of the Eu²⁺ luminescence in different phases of (Sr0.98-xBaxEu0.02)Si₂O₂N₂:Eu from −40 cm⁻¹/kbar to 0 cm⁻¹/kbar have been observed. This effect is explained by different interaction of the Eu²⁺ 5d electron with the second coordination sphere around the impurity cations.

UV/VUV switch-driven color-reversal effect for Tb-activated phosphors

The remarkable narrow-band emission of trivalent lanthanide-doped phosphors excited by the vacuum ultraviolet (VUV) radiation lines of Xe atoms/Xe₂ molecules at 147/172 nm are extensively investigated in the development of plasma display panels and Hg-free fluorescent lamps, which are frequently used in our daily lives. Numerous solid materials, particularly Tb³⁺-doped oxides, such as silicates, phosphates and borates, are efficient green/blue sources with color-tunable properties. The excitation wavelength and rare earth concentration are usually varied to optimize efficiency and the luminescent properties. However, some underlying mechanisms for the shift in the emission colors remain unclear. The present study shows that a UV/VUV switch systematically controls the change in the phosphor (Ba₃Si₆O₁₂N₂:Tb) photoluminescence from green to blue, resulting in a green emission when the system is excited with UV radiation. However, a blue color is observed when the radiation wavelength shifts to the VUV region. Thus, a configurational coordinate model is proposed for the color-reversal effect. In this model, the dominant radiative decay results in a green emission under low-energy UV excitation from the ⁵D₄ state of the f-f inner-shell transition in the Tb system. However, under high-energy VUV excitation, the state switches into the ⁵D₃ state, which exhibits a blue emission. This mechanism is expected to be generally applicable to Tb-doped phosphors and useful in adjusting the optical properties against well-known cross-relaxation processes by varying the ratio of the green/blue contributions.

Effects of Ca Content on Formation and Photoluminescence Properties of CaAlSiN₃:Eu2+ Phosphor by Combustion Synthesis

Effects of Ca content (in the reactant mixture) on the formation and the photoluminescence properties of CaAlSiN₃:Eu²⁺ phosphor (CASIN) were investigated by a combustion synthesis method. Ca, Al, Si, Eu₂O₃, NaN₃, NH₄Cl and Si₃N₄ powders were used as the starting materials and they were mixed and pressed into a compact which was then wrapped up with an igniting agent (i.e., Mg + Fe₃O₄). The compact was ignited by electrical heating under a N₂ pressure of ≤1.0 MPa. By keeping the molar ratios of Al and Si (including the Si powder and the Si in Si₃N₄ powder) both at 1.00 and that of Eu₂O₃ at 0.02, XRD (X-ray diffraction) coupled with TEM-EDS (transmission electron microscope equipped with an energy-dispersive X-ray spectroscope) and SAED (selected area electron diffraction) measurements show that AlN:Eu²⁺ and Ca-α-SiAlON:Eu²⁺ are formed as the major phosphor products when the Ca molar ratio (denoted by Y) is equal to 0.25 and AlN:Eu²⁺ and Ca-α-SiAlON:Eu²⁺ could not be detected at Y ≥ 0.75 and ≥1.00, respectively. CASIN (i.e., CaAlSiN₃:Eu²⁺) becomes the only phosphor product as Y is increased to 1.00 and higher. The extent of formation of CASIN increases with increasing Y up to 1.50 and begins to decrease as Y is further increased to 1.68. While the excitation wavelength regions are similar at various Y, the emission wavelength regions vary significantly as Y is increased from 0.25 to 1.00 due to different combinations of phosphor phases formed at different Y. The emission intensity of CASIN was found to vary with Y in a similar trend to its extent of formation. The Ca and Eu contents (expressed as molar ratios) in the synthesized products were found to increase roughly with increasing Y but were both lower than the respective Ca and Eu contents in the reactant mixtures.

Significant colour tuning via energy transfer in Eu2+ solely doped La2.5Ca1.5Si12O4.5N16.5

A large shift of the emission colour from blue-green to orange is observed in La_2.5Ca_1.5−yEu_ySi₁₂O_4.5N_16.5 phosphors, due to increased energy transfer between Eu²⁺ ions at different crystal sites.

Recent progress in low-voltage cathodoluminescent materials: synthesis, improvement and emission properties

Nowadays there are several technologies used for flat panel displays (FPDs) and the development of FPDs with enhanced energy efficiency and improved display quality is strongly required. Field emission displays (FEDs) have been considered as one of the most promising next generation flat panel display technologies due to their excellent display performance and low energy consumption. For the development of FEDs, phosphors are irreplaceable components. In the past decade, the study of highly efficient low-voltage cathodoluminescent materials, namely FED phosphors, has become the focus of enhancing energy efficiency and realizing high-quality displays. This review summaries the recent progress in the chemical synthesis and improvement of novel, rare-earth and transition metal ions activated inorganic cathodoluminescent materials in powder and thin film forms. The discussion is focused on the modification of morphology, size, surface, composition and conductivity of phosphors and the corresponding effects on their cathodoluminescent properties. Special emphases are given to the selection of host and luminescent centers, the adjustment of emission colors through doping concentration optimization, energy transfer and mono- or co-doping activator ions, the improvement of chromaticity, color stability and color gamut as well as the saturation behavior and the degradation behavior of phosphors under the excitation of a low-voltage electron beam. Finally, the research prospects and future directions of FED phosphors are discussed with recommendations to facilitate the further study of new and highly efficient low-voltage cathodoluminescent materials.

Luminescent nitridophosphates CaP2 N4 :Eu(2+) , SrP2 N4 :Eu(2+) , BaP2 N4 :Eu(2+) , and BaSr2 P6 N12 :Eu(2.)

Nitridophosphates MP2 N4 :Eu(2+) (M=Ca, Sr, Ba) and BaSr2 P6 N12 :Eu(2+) have been synthesized at elevated pressures and 1100-1300 °C starting from the corresponding azides and P3 N5 with EuCl2 as dopant. Addition of NH4 Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single-crystal X-ray diffraction data (CaP2 N4 :Eu(2+) (P63 , no. 173), a=16.847(2), c=7.8592(16) Å, V=1931.7(6) Å(3) , Z=24, 2033 observed reflections, 176 refined parameters, wR2 =0.096). Upon excitation by UV light, luminescence due to parity-allowed 4f(6) ((7) F)5d(1) →4f(7) ((8) S7/2 ) transition was observed in the orange (CaP2 N4 :Eu(2+) , λmax =575 nm), green (SrP2 N4 :Eu(2+) , λmax =529 nm), and blue regions of the visible spectrum (BaSr2 P6 N12 :Eu(2+) and BaP2 N4 :Eu(2+) , λmax =450 and 460 nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline-earth ions. The corresponding full width at half maximum values (2240-2460 cm(-1) ) are comparable to those of other known Eu(2+) -doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba3 P5 N10 Br:Eu(2+) , this investigation represents the first report on the luminescence of Eu(2+) -doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu(2+) -doped nitridophosphates may have the potential to be further developed into efficient light-emitting diode phosphors.

Ba3P5N10Br:Eu(2+): a natural-white-light single emitter with a zeolite structure type

Illumination sources based on phosphor-converted light emitting diode (pcLED) technology are nowadays of great relevance. In particular, illumination-grade pcLEDs are attracting increasing attention. Regarding this, the application of a single warm-white-emitting phosphor could be of great advantage. Herein, we report the synthesis of a novel nitridophosphate zeolite Ba3P5N10Br:Eu(2+). Upon excitation by near-UV light, natural-white-light luminescence was detected. The synthesis of Ba3P5N10Br:Eu(2+) was carried out using the multianvil technique. The crystal structure of Ba3P5N10Br:Eu(2+) was solved and refined by single-crystal X-ray diffraction analysis and confirmed by Rietveld refinement and FTIR spectroscopy. Furthermore, spectroscopic luminescence measurements were performed. Through the synthesis of Ba3P5N10Br:Eu(2+), we have shown the great potential of nitridophosphate zeolites to serve as high-performance luminescence materials.

Red luminescence and ferromagnetism in europium oxynitridosilicates with a β-K2SO4 structure

LaSrSiO₃N and LaBaSiO₃N are the first examples of nitride-based alkaline earth orthosilicates with β-K₂SO₄ structure, and they show red-orange luminescence after activation with Eu²⁺. The analogous compound LaEuSiO₃N is, in addition to a red phosphor material, a soft ferromagnet with a Curie temperature of 3 K.

Effect of a solid solution of AlN on the crystal structure and optical properties of LiSi2N3:Eu phosphors

The solid solutions could be the useful way to improve the luminescence intensity of LiSi₂N₃:Eu phosphors.

Double substitution induced tunable photoluminescence in the Sr2Si5N8:Eu phosphor lattice

The incorporation of La³⁺–Al³⁺ ion pairs into Sr_1.95Eu_0.05Si₅N₈ leads to an additional emission band with maximum at about 760 nm.

Structural and luminescence studies of the new nitridomagnesoaluminate CaMg2AlN3

The luminescent nitridomagnesoaluminate, CaMg₂AlN₃, was synthesized in a closed system by solid-state reaction from binary nitrides. Structure solution was aided by ultrahigh-field solid-state NMR spectroscopy and DFT calculations.

Recent progress in luminescence tuning of Ce3+and Eu2+-activated phosphors for pc-WLEDs

This review is devoted to several approaches to realize spectral tuning for improving the luminescence performance of Ce³⁺and Eu²⁺-activated pc-WLED phosphors.

Crystal Structures of New Ammonium 5-Aminotetrazolates

The crystal structures of three salts of anionic 5-aminotetrazole are described. The tetramethylammonium salt (P[Formula: see text]) forms hydrogen-bonded ribbons of anions which accept weak C-H⋯N contacts from the cations. The cystamine salt (C2/c) shows wave-shaped ribbons of anions linked by hydrogen bonds to screw-shaped dications. The tetramethylguanidine salt (P2₁/c) exhibits layers of anions hydrogen-bonded to the cations.

Domination of second-sphere shrinkage effect to improve photoluminescence of red nitride phosphors

Red Ca0.99Al(1-4δ/3-x)Si(1+δ+x)N(3-x)C(x):Eu(2+)0.01 (δ = 0.345; x = 0-0.2) nitride phosphors exhibit a blue-shifted emission with increased eye sensitivity function and excellent thermal stability. The variations in the photoluminescence in the Ca0.99Al(1-4δ/3-x)Si(1+δ+x)N(3-x)C(x):Eu(2+)0.01 (δ = 0.345; x = 0-0.2) system are thoroughly investigated. The enhanced emission energy and the improved thermal stability with increasing x are dominated by the second-sphere shrinkage effect via the substitution of small Si(4+) for large Al(3+) with simultaneous charge compensation. Related proofs of the second-sphere shrinkage effect control for photoluminescence are confirmed via high-resolution neutron powder diffraction, EXAFS, and (29)Si solid-state NMR techniques.

A high-pressure polymorph of phosphorus nitride imide

Phosphorus nitride imide, PN(NH), is of great scientific importance because it is isosteric with silica (SiO2). Accordingly, a varied structural diversity could be expected. However, only one polymorph of PN(NH) has been reported thus far. Herein, we report on the synthesis and structural investigation of the first high-pressure polymorph of phosphorus nitride imide, β-PN(NH); the compound has been synthesized using the multianvil technique. By adding catalytic amounts of NH4Cl as a mineralizer, it became possible to grow single crystals of β-PN(NH), which allowed the first complete structural elucidation of a highly condensed phosphorus nitride from single-crystal X-ray diffraction data. The structure was confirmed by FTIR and (31)P and (1)H solid-state NMR spectroscopy. We are confident that high-pressure/high-temperature reactions could lead to new polymorphs of PN(NH) containing five-fold- or even six-fold-coordinated phosphorus atoms and thus rivalling or even surpassing the structural variety of SiO2.

Narrow-band red-emitting Sr[LiAl₃N₄]:Eu²⁺ as a next-generation LED-phosphor material

To facilitate the next generation of high-power white-light-emitting diodes (white LEDs), the discovery of more efficient red-emitting phosphor materials is essential. In this regard, the hardly explored compound class of nitridoaluminates affords a new material with superior luminescence properties. Doped with Eu(2+), Sr[LiAl3N4] emerged as a new high-performance narrow-band red-emitting phosphor material, which can efficiently be excited by GaN-based blue LEDs. Owing to the highly efficient red emission at λ(max) ~ 650 nm with a full-width at half-maximum of ~1,180 cm(-1) (~50 nm) that shows only very low thermal quenching (>95% relative to the quantum efficiency at 200 °C), a prototype phosphor-converted LED (pc-LED), employing Sr[LiAl3N4]:Eu(2+) as the red-emitting component, already shows an increase of 14% in luminous efficacy compared with a commercially available high colour rendering index (CRI) LED, together with an excellent colour rendition (R(a)8 = 91, R9 = 57). Therefore, we predict great potential for industrial applications in high-power white pc-LEDs.

New yellow-emitting nitride phosphor SrAlSi4N7:Ce3+ and important role of excessive AlN in material synthesis

Synthesis and luminescent properties of Ce(3+)-doped SrAlSi4N7 yellow-emitting phosphor are reported. In comparison with YAG: Ce(3+), the phosphor exhibits smaller thermal quenching and a broader emission band centering at 555 nm with a bandwidth as large as 115 nm, being suitable for fabricating high color rendering white LED. It is observed in material synthesis that intense luminescence can be achieved only in case of excessive AlN in the raw materials. The role of the excessive AlN is studied. The mechanism for existence of edge-sharing [AlN4] tetrahedral, which is unreasonable according to the aluminum avoidance principle, is discussed in detail.