In this work, we present a comprehensive study of the luminescence relaxation mechanism and the associated spectral broadening in a series of Eu2+-doped narrow-band phosphors. It is highlighted that the commonly used full-width at half-maximum (fwhm) is no longer a sensitive measure for quantifying the emission bandwidth of these materials. A thorough understanding of the factors contributing to the narrow bandwidth requires an explicit treatment of the magnetic structure of the ground and emissive excited state manifolds. This requires incorporating spin-orbit coupling effects using wave function-based methods such as the complete active space self-consistent field combined with second-order N-electron valence state perturbation theory (CASSCF/NEVPT2). In addition, for the associated excited state dynamics calculations, one needs to consider vibronic coupling interactions on the basis of Franck-Condon (FC), Herzberg-Teller (HT), and, when necessary, pseudo Jahn-Teller (PJT) coupling effects. Our analysis underscores that understanding and controlling the synergistic roles of these "static" and "dynamic" effects are essential for accurately assessing the narrow band emission relaxation in these systems. We show that these results can, in principle, be generalized to an arbitrary set of narrow-band phosphor candidates and can potentially aid the experimental efforts toward developing novel phosphors with enhanced luminescent properties.

Light-emitting diodes (LEDs) producing pure, highly saturated colors are the industry standard for efficient backlighting of high-color gamut displays. Vivid color reproduction, matching the eye's perception of nature, is the central paradigm in the design of narrow-band emitting phosphors. To cover a wide range of naturally occurring color tones, expansion of the color gamut in the green spectral region, and therefore an advanced applicable green phosphor, is highly desired. Herein, the oxonitridoberyllosilicate Ba[BeSiON2]:Eu2+ showing outstanding narrow-band green emission (lambda(max) approximate to 526 nm with FWHM approximate to 1600 cm(-1) (approximate to 45 nm), x = 0.212, y = 0.715) when excited with InGaN-based blue LEDs is presented. High quantum efficiency and low thermal quenching (>90% rel. quantum efficiency at 100 degrees C) as well as excellent scalability make the material suitable for industrial application in high color-gamut LED displays. A prototype phosphor-converted-LED (pc-LED), with green-emitting Ba[BeSiON2]:Eu2+ and K2SiF6:Mn4+ as red phosphor shows an extraordinary coverage in the CIE 1931 color space of 109% compared to the DCI-P3 standard, topping the widely applied beta-SiAlON:Eu2+ phosphor (104%), making it suitable for use in phone displays, monitors, and television screens.

The structural variability of a compound class is an important criterion for the research into phosphor host lattices for phosphor-converted light-emitting diodes (pc-LEDs). Especially, nitridophosphates and the related class of imidonitridophosphates are promising candidates. Recently, the ammonothermal approach has opened a systematic access to this substance class with larger sample quantities. We present the successful ammonothermal synthesis of the imidonitridophosphate Ba4P4N8(NH)2:Eu2+. Its crystal structure is solved by X-ray diffraction and it crystallizes in space group Cc (no. 9) with lattice parameters a=12.5250(3), b=12.5566(4), c=7.3882(2) Å and β=102.9793(10)°. For the first time, adamantane-type (imido)nitridophosphate anions [P4N8(NH)2]8- are observed next to metal ions other than alkali metals in a compound. The presence of imide groups in the structure and the identification of preferred positions for the hydrogen atoms are performed using a combination of quantum chemical calculations, Fourier-transform infrared, and solid-state NMR spectroscopy. Eu2+ doped samples exhibit cyan emission (λmax=498 nm, fwhm=50 nm/1981 cm-1) when excited with ultraviolet light with an impressive internal quantum efficiency (IQE) of 41 %, which represents the first benchmark for imidonitridophosphates and is promising for potential industrial application of this compound class.

In the field of nitride phosphors, which are crucial for phosphor-converted light-emitting diodes, mixed tetrahedral networks hold a significant position. With respect to the wide range of compositions, the largely unexplored (Si, P)-N networks are investigated as potential host structures. In this work, two highly condensed structures, namely Sr2SiP2N6 and Sr5Si2P6N16 are reported to address the challenges that arise from the similarities of the network-forming cations Si4+ and P5+ in terms of charge, ionic radius, and atomic scattering factor, a multistep workflow is employed to elucidate their structure. Using single-crystal X-ray diffraction, energy-dispersive X-ray spectroscopy (EDX), atomic-resolution scanning transmission electron microscopy (STEM)-EDX maps, and straightforward crystallographic calculations, it is found that Sr2SiP2N6 is the first ordered, and Sr5Si2P6N16 the first disordered, anionic tetrahedral (Si, P)-N network. After doping with Eu2+, Sr2SiP2N6:Eu2+ shows narrow cyan emission (lambda(max) = 506 nm, fwhm = 60 nm/2311 cm(-1)), while for Sr5Si2P6N16:Eu2+ a broad emission with three maxima at 534, 662, and 745 nm upon irradiation with ultraviolet light is observed. An assignment of Sr sites as probable positions for Eu2+ and their relation to the emission bands of Sr5Si2P6N16:Eu2+ is discussed.

Tetrahedron-based nitrides offer a wide range of properties and applications. Highly condensed nitridophosphates are examples of nitrides that exhibit fascinating luminescence properties when doped with Eu 2+ , making them appealing for industrial applications. Here, we present the first nitridomagnesophosphate solid solution series Ba 3− x Sr x [Mg 2 P 10 N 20 ] : Eu 2+ ( x =0–3), synthesized by a high-pressure high-temperature approach using the multianvil technique (3 GPa, 1400 °C). Starting from the binary nitrides P 3 N 5 and Mg 3 N 2 and the respective alkaline earth azides, we incorporate Mg into the P/N framework to increase the degree of condensation κ to 0.6, the highest observed value for alkaline earth nitridophosphates. The crystal structure was elucidated by single-crystal X-ray diffraction, powder X-ray diffraction, energy-dispersive X-ray spectroscopy (EDX), and solid-state NMR. DFT calculations were performed on the title compounds and other related highly condensed nitridophosphates to investigate the influence of Mg in the P/N network. Eu 2+ -doped samples of the solid solution series show a tunable narrow-band emission from cyan to green (492–515 nm), which is attributed to the preferred doping of a single crystallographic site. Experimental confirmation of this assumption was provided by overdoping experiments and STEM-HAADF studies on the series as well on the stoichiometric compound Ba 2 Eu[Mg 2 P 10 N 20 ] with additional atomic resolution energy-dispersive X-ray spectroscopy (EDX) mapping.

Nitridophosphates have emerged as promising host compounds in the field of solid-state lighting. Their industrial relevance has increased significantly, mainly due to recent advances in synthetic approaches under medium-pressure (MP) conditions, including ammonothermal synthesis and hot isostatic pressing (HIP). In this study, we report on the synthesis and characterization of the quaternary representatives Ca x Li 10−2 x P 4 N 10 ( x =2, 2.7, 4) and Sr 3 Li 4 P 4 N 10 , prepared via a simplified ion exchange reaction under MP conditions, starting from the nitridophosphate-based lithium ion conductor Li 10 P 4 N 10 . The synthesis route allowed for the preservation of the anionic [P 4 N 10 ] 10− structural motif of the starting material, while simultaneously introducing potential doping sites for Eu 2+ by incorporating divalent alkaline earth cations (Ca 2+ /Sr 2+ ). Upon excitation of Eu 2+ doped samples with blue light, strong luminescence due to parity-allowed 4f 6 ( 7 F)5d 1 →4f 7 ( 8 S 7/2 ) transition can be observed in the red (Ca 2 Li 6 P 4 N 10  : Eu 2+ : λ max =626 nm), yellow/orange (Ca 2.7 Li 4.6 P 4 N 10  : Eu 2+ : λ max1 =506 nm, λ max2 =592 nm and Sr 3 Li 4 P 4 N 10  : Eu 2+ : λ max =596 nm) and green (Ca 4 Li 2 P 4 N 10  : Eu 2+ : λ max =546 nm) spectral regions of the visible light. The compounds presented, together with the simplified synthetic approach, demonstrate the significant potential of ion exchange on Li ion conductors for the development of novel nitridophosphates in the future.

In the search for materials for high-efficiency lighting applications, the color-point tuning of phosphors for inorganic phosphor converted LEDs (pcLEDs) is of special interest. We expand the recently explored phosphor class of SiBeONs (oxonitridoberyllosilicates) by the synthesis and characterization of SrBe1-xSi2+xO3-2xN2+2x:Eu2+. High temperature synthesis, starting from Sr2N, BeO, SiO2 and Si3N4, yields the target phase as the main product. Upon doping with Eu2+, the pale blue crystals exhibit blue luminescence with emission at 456 nm and a full width at half maximum (fwhm) of 66 nm/3108 cm(-1). The structure is an ordered variant of the LaSi3N5 structure type and was elucidated by single-crystal X-ray diffraction data. The network in SrBe1-xSi2+xO3-2xN2+2x:Eu2+ is highly condensed with a condensation degree of kappa=0.6 comprising corner-sharing [MX4] (M=Be, Si; X=O, N) tetrahedra, with mixed occupancies on both the ligand and central metal sites.

This study presents the synthesis and characterization of oxonitridosilicate phosphates Sr3SiP3O2N7, Sr5Si2P4ON12, and Sr16Si9P9O7N33 as the first of their kind. These compounds were synthesized under high-temperature (1400 °C) and high-pressure (3 GPa) conditions. A unique structural feature is their common fundamental building unit, a vierer single chain of (Si, P)(O, N)4 tetrahedra. All tetrahedra comprise substitutional disorder which is why we refer to it as the fundamental disorder unit (FDU). We classified four different FDU motifs, revealing systematic bonding patterns. Including literature known Sr5Si2P6N16, three of the four patterns were found in the presented compounds. Common techniques like single-crystal X-ray diffraction (SCXRD), elemental analyses, and 31P nuclear magnetic resonance (NMR) spectroscopy were utilized for structural analysis. Additionally, low-cost crystallographic calculations (LCC) provided insights into the structure of Sr16Si9P9O7N33 where NMR data were unavailable due to the lack of bulk samples. The optical properties of these compounds, when doped with Eu2+, were investigated using photoluminescence excitation (PLE), photoluminescence (PL) measurements, and density functional theory (DFT) calculations. Factors influencing the emission properties, including thermal quenching mechanisms, were discussed. This research reveals the new class of oxonitridosilicate phosphates with unique systematic structural features that offer potential for theoretical studies of luminescence and band gap tuning in insulators.

In this study, the structural and luminescence properties of SrSi2PN5:Eu2+ and its analogues within the LaSi3N5 structure type are investigated by using a variety of analytical techniques, including X-ray diffraction (XRD), P-31 solid-state NMR, and powder neutron diffraction. We are exploring the challenges of chemical similarity and low X-ray contrast between the key elements to extend our analytical capabilities by powder neutron diffraction (PND) for (Si,P)-N networks. In principle, PND shows greater differences in scattering contrasts for O/N and Si/P, although it does not surpass standard powder XRD in elemental discrimination of Si/P within the network. The Eu2+ doping of SrSi2PN5 demonstrates the potential for tunable optical applications within the group of LaSi3N5 analogous materials. Our results contribute to the understanding of the structural diversity and luminescence mechanisms of nitridosilicate phosphates and emphasize the importance of a comprehensive analytical approach in materials science, with implications for the future development of optoelectronic devices.

We have previously presented a computational protocol that is based on an embedded cluster model and operates in the framework of TD-DFT in conjunction with the excited state dynamics (ESD) approach. The protocol is able to predict the experimental absorption and emission spectral shapes of Eu2+-doped phosphors. In this work, the applicability domain of the above protocol is expanded to Eu2+-doped phosphors bearing multiple candidate Eu doping centers. It will be demonstrated that this protocol provides full control of the parameter space that describes the emission process. The stability of Eu doping at various centers is explored through local energy decomposition (LED) analysis of DLPNO-CCSD(T) energies. This enables further development of the understanding of the electronic structure of the targeted phosphors, the diverse interactions between Eu and the local environment, and their impact on Eu doping probability, and control of the emission properties. Hence, it can be employed to systematically improve deficiencies of existing phosphor materials, defined by the presence of various intensity emission bands at undesired frequencies, towards classes of candidate Eu2+-doped phosphors with desired narrow band red emission. For this purpose, the chosen study set consists of three UCr4C4-based narrow-band phosphors, namely the known alkali lithosilicates RbNa[Li3SiO4]2:Eu2+ (RNLSO2), RbNa3[Li3SiO4]4:Eu2+ (RNLSO) and their isotypic nitridolithoaluminate phosphors consisting of CaBa[LiAl3N4]2:Eu2+ (CBLA2) and the proposed Ca3Ba[LiAl3N4]4:Eu2+ (CBLA), respectively. The theoretical analysis presented in this work led us to propose a modification of the CBLA2 phosphor that should have improved and unprecedented narrow band red emission properties. Finally, we believe that the analysis presented here is important for the future rational design of novel Eu2+-doped phosphor materials, with a wide range of applications in science and technology.

Oxonitridophosphates exhibit the potential for broad structural diversity, making them promising host-compounds in phosphor-converted light-emitting diode applications. The novel monophyllo-oxonitridophosphate beta-MgSrP3N5O2 was obtained by using the high-pressure multianvil technique. The crystal structure was solved and refined based on single-crystal X-ray diffraction data and confirmed by powder X-ray diffraction. beta-MgSrP3N5O2 crystallizes in the orthorhombic space group Cmme (no. 67, a=8.8109(6), b=12.8096(6), c=4.9065(3) angstrom, Z=4) and has a structure related to that of Ba2CuSi2O7. DFT calculations were performed to investigate the phase transition from alpha- to beta-MgSrP3N5O2 and to confirm the latter as the corresponding high-pressure polymorph. Furthermore, the luminescence properties of Eu2+ doped samples of both polymorphs were investigated and discussed, showing blue and cyan emission, respectively (alpha-MgSrP3N5O2; lambda(max)=438 nm, fwhm=46 nm/2396 cm(-1); beta-MgSrP3N5O2; lambda(max)=502 nm, fwhm=42 nm/1670 cm(-1)).

In this work, we present the synthesis, characterization, and optical properties of Sr5Si7P2N16:Eu2+, the first tetrahedral (Si,P)-N network in which Si occupies more than 50% of the tetrahedra. While past studies have shown progress with anionic (Si,P)-N networks, the potential of silicon-rich compounds remains untapped. The synthesized compound Sr5Si7P2N16 exhibits a unique mixture of substitutional order and positional disorder within its network. The analytical challenges posed by the similarities between Si4+ and P5+, along with the network's disorder, were overcome by combining single-crystal X-ray diffraction and scanning transmission electron microscopy EDX mapping. Low-cost crystallographic calculations provided additional insights into the identification of tetrahedral occupations in mixed networks. Luminescence investigations on Sr5Si7P2N16:Eu2+ revealed yellow emission, adding to the known blue, green, and orange emission maxima of Sr-(Si,P)-N networks, highlighting the variability of such compounds.

The oxonitridosilicate La7Sr[Si10N19O3] : Eu2+ and its substitutional variants RE(8-x)AE(x)[Si10N20-xO2+x] : Eu2+ with RE=La, Ce; AE=Ca, Sr, Ba and 0 <= x <= 2 were synthesized starting from REN, SrN/Ca3N2/Ba2N, SiO2, amorphous Si3N4 and Eu2O3 as doping agent at 1600 degrees C in a radiofrequency furnace. The crystal structure of La7Sr[Si10N19O3] was solved and refined based on single-crystal X-ray diffraction data. La7Sr[Si10N19O3] crystallizes in the orthorhombic space group Pmn2(1) (no. 31). The crystal structures of the isotypic compounds RE(8-x)AE(x)[Si10N20-xO2+x] were confirmed by Rietveld refinements based on powder X-ray diffraction data using the single-crystal data of La7Sr[Si10N19O3] as starting point. Crystal structure elucidation reveals a 3D network of vertex sharing SiN4 and SiN2(N1/2-x/4O1/2+x/4)(2) (0 <= x <= 2) tetrahedra. When excited with UV to blue light, La7Sr[Si10N19O3] : Eu2+ shows amber luminescence with lambda(em)=612 nm and fwhm=84 nm/2194 cm(-1), which makes it interesting for application in amber phosphor-converted light emitting diodes.

An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The nitridoberylloaluminate Ba-2[BeAl3N5]:Eu2+ and solid solutions Sr2-xBax[BeAl3N5]:Eu2+ (x=0.5, 1.0, 1.5) were synthesized in a hot isostatic press (HIP) under 50 MPa N-2 atmosphere at 1200 degrees C. Ba-2[BeAl3N5]:Eu2+ crystallizes in tri-clinic space group P (1) over bar (no. 2) (Z=2, a=6.1869(10), b= 7.1736(13), c= 8.0391(14) angstrom, alpha = 102.754(8), beta = 112.032(6), gamma = 104.765(7)degrees), which was determined from single-crystal X-ray diffraction data. The lattice parameters of the solid solution series have been obtained from Rietveld refinements and show a nearly linear dependence on the atomic ratio Sr:Ba. The electronic properties and the band gaps of M-2[BeAl3N5](M=Sr, Ba) have been investigated by a combination of soft X-ray spectroscopy and density functional theory (DFT) calculations. Upon irradiation with blue light (440-450 nm), the nitridoberylloaluminates exhibit intense orange to red luminescence, which can be tuned between 610 and 656 nm (fwhm =1922-2025 cm(-1) (72-87 nm)). In contrast to the usual trend, the substitution of the smaller Sr2+= by larger Ba" leads to an inverse-tunable luminescence to higher wavelengths. Low-temperature luminescence measurements have been performed to exclude anomalous emission.

In this work, we present a computational protocol that is able to predict the experimental absorption and emission spectral shapes of Eu2+-doped phosphors. The protocol is based on time-dependent density functional theory and operates in conjunction with an excited-state dynamics approach. It is demonstrated that across the study set consisting of representative examples of nitride, oxo-nitride, and oxide Eu2+-doped phosphors, the energy distribution and the band shape of the emission spectrum are related to the nature of the 4f-5d transitions that are probed in the absorption process. Since the 4f orbitals are very nearly nonbonding, the decisive quantity is the covalency of the 5d acceptor orbitals that become populated in the electronically excited state that leads to emission. The stronger the (anti) bonding interaction between the lanthanide and the ligands is in the excited state, the larger will be the excited state distortion. Consequently, the corresponding emission will get broader due to the vibronic progression that is induced by the structural distortion. In addition, the energy separation of the absorption bands that are dominated by states with valence 4f-5d and a metal to ligand charge transfer character defines a measure for the thermal quenching of the studied Eu2+-doped phosphors. Based on this analysis, simple descriptors are identified that show a strong correlation with the energy position and bandwidth of the experimental emission bands without the need for elaborate calculations. Overall, we believe that this study serves as an important reference for designing new Eu2+-doped phosphors with desired photoluminescence properties.

An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Our study accesses directly information on electronic and optical properties of phosphors such as intragap states and radiative energy levels. It further describes how the applied methods inform design and understanding of new pc-LED phosphors.

Angewandte Chemie International EditionVolume 60, Issue 9 p. 4385-4405 Graphical AbstractFree Access Graphical Abstract: Angew. Chem. Int. Ed. 9/2021 First published: 16 February 2021 https://doi.org/10.1002/anie.202180911AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume60, Issue9February 23, 2021Pages 4385-4405 RelatedInformation

The nitridosilicate CaLu[Si4N7-2xCxOx] (x approximate to 0.3) was synthesized by carbothermal reduction and nitridation starting from CaH2, Lu2O3, graphite and amorphous Si3N4 at 1550 degrees C in a radiofrequency furnace. CaLu[Si4N7-2xCxOx] (x approximate to 0.3) crystallizes isotypically to many previously known (MMSi4N7)-M-II-Si-III compounds in the space group P6(3)mc, as was confirmed by Rietveld refinement based on powder X-ray diffraction data. Incorporation of carbon into the crystal structure as a result of the carbothermal synthesis route was confirmed by C-13 and Si-29 MAS NMR spectroscopy. For the first time in the (MMSi4N7)-M-II-Si-III compound class, complementary EDX measurements suggest that simultaneous incorporation of oxygen compensates for the negative charge excess induced by carbon, resulting in an adjusted sum formula, CaLu[Si4N7-2xCxOx] (x approximate to 0.3). When excited with UV-to-blue light, CaLu[Si4N7-2xCxOx] (x approximate to 0.3) shows an emission maximum in the blue spectral region (lambda(em)=484 nm; fwhm=4531 cm(-1)) upon doping with Ce3+, whereas Eu2+-doped CaLu[Si4N7-2xCxOx] (x approximate to 0.3) exhibits a yellow-green emission (lambda(em)=546 nm; fwhm=3999 cm(-1)).