Luminescent Sites Research Articles

Optical characterization of GaN:Eu microcrystals grown by the ammonothermal method

Eu-doped gallium nitride (GaN:Eu) microcrystals with a wurtzite crystal structure were synthesized using the ammonothermal method. The Eu concentration of GaN:Eu microcrystals estimated by glow discharge mass spectrometry (GDMS) was 5.8 × 1020 atoms/cm3. The morphology of GaN:Eu microcrystals was characterized by scanning electron microscopy (SEM). The exposed crystal faces of GaN:Eu microcrystals were identified as {10−10}, {10−11}, (000−1), and (0001), respectively. The photoluminescence excitation (PLE), photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectra of GaN:Eu microcrystals revealed two luminescent sites of Eu3+ ions, designated as Eu0 and Eu1. The Eu0 was excited in the range of 300 nm to 420 nm, resulting in the observation of four characteristic luminescence peaks at 599 nm (5D0-7F1), 620 nm (5D0-7F2), 632 nm (5D1-7F4), and 663 nm (5D0-7F3). The Eu1 was associated with O2- ions and emitted light at specific excitation wavelengths. The main luminescence peak of the Eu1 was located at 614 nm, accompanied with characteristic peaks at 578 nm, 591 nm, and 698 nm. In view of the distinct luminescence properties of the Eu0 and the Eu1, the energy transfer processes of two luminescence sites were proposed.

Robust and orange-yellow-emitting Sr-rich polytypoid α-SiAlON (Sr3Si24Al6N40:Eu2+) phosphor for white LEDs

ABSTRACT Nitrides and oxynitrides isostructural to α-Si3N4 (M-α-SiAlON, M = Sr, Ca, Li) possess superb thermally stable photoluminescence (PL) properties, making them reliable phosphors for high-power solid-state lighting. However, the synthesis of phase-pure Sr-α-SiAlON still remains a great challenge and has only been reported for Sr below 1.35 at.% as the large size of Sr2+ ions tends to destabilize the α-SiAlON structure. Here, we succeeded to synthesize the single-phase powders of a unique ‘Sr-rich’ polytypoid α-SiAlON (Sr3Si24Al6N40:Eu2+) phosphor with three distinctive Sr/Eu luminescence sites using a solid-state remixing-reannealing process. The Sr content of this polytypoid structure exceeds those of a few previously reported structures by over 200%. The phase purity, composition, structure, and PL properties of this phosphor were investigated. A single phase can be obtained by firing the stoichiometric mixtures of all-nitride precursors at 2050°C under a 0.92 MPa N2 atmosphere. The Sr3Si24Al6N40:Eu2+ shows an intense orange-yellow emission, with the emission maximum of 590 nm and internal/external quantum efficiency of 66%/52% under 400 nm excitation. It also has a quite small thermal quenching, maintaining 93% emission intensity at 150°C. In comparison to Ca-α-SiAlON:Eu2+, this Sr counterpart shows superior quantum efficiency and thermal stability, enabling it to be an interesting orange-yellow down-conversion luminescent material for white LEDs. The experimental confirmation of the existence of such ‘Sr-rich’ SiAlON systems, in a single-phase powder form, paves the way for the design and synthesis of novel ‘Sr-rich’ SiAlON-based phosphor powders with unparalleled properties.

Simultaneous NIR Emission and Thermal Stability Enhancement in Garnet‐Type NIR Phosphors through the Synergistic Effect of Lattice Distortion and Enhanced Rigidity

AbstractEven though there have been significant advancements in the development of Cr3+‐activated near‐infrared (NIR) phosphors, the challenge still remains to develop highly efficient and thermally stable NIR phosphors. Here, the Ca4‐xZnxHfGe3O12:0.03Cr3+ solid solution phosphors with 834–806 nm NIR emission are constructed by substituting Zn2+ for Ca2+, thereby facilitating the formation of [ZnO6] luminescence site. The coexistence of [HfO6] and [Zn/CaO6] luminescence centers is confirmed through DFT calculation, time‐resolved photoluminescence (TRPL) spectroscopy, and low‐temperature‐photoluminescence (77 K) spectroscopy. The formation of [ZnO6] effectively resolves the issue of lattice mismatch between Cr3+ and Ca2+. Furthermore, the simultaneous enhancement of luminescence intensity and thermal stability is realized through a synergistic combination of lattice distortion and rigidity enhancement. By optimizing the substitution concentration of Cr3+, the internal quantum efficiency (IQE) of 92% and an external quantum efficiency (EQE) of 29% are finally achieved. Meanwhile, the thermal stability is also enhanced from 59%@400 K (x = 0) to 81%@400 K (x = 0.8). The developed NIR phosphor‐converted light‐emitting diodes (pc‐LEDs) exhibit promising prospects in the fields of security, biomedicine, non‐destructive testing and rapid identification.

An efficiently excited Eu3+ luminescent site formed in Eu,O-codoped GaN

For the development of III-nitride-semiconductor-based monolithic micro-light-emitting diode (LED) displays, Eu,O-codoped GaN (GaN:Eu,O) is a promising material candidate for the red LEDs. The luminescence efficiency of Eu-related emission strongly depends on the local atomic structure of Eu ions. Our previous research has revealed that post-growth thermal annealing is an effective method for reconfiguring luminescent sites, leading to a significant increase in light output. We observed the preferential formation of a site with a peak at ∼2.004 eV by the annealing process. In this study, we demonstrate that it is a previously unidentified independent site (OMVPE-X) using combined excitation–emission spectroscopy and time-resolved photoluminescence measurements. In addition, we perform excitation power-dependent photoluminescence measurements and show that this OMVPE-X site dominates the emission at a low excitation power region despite its small relative abundance, suggesting a high excitation efficiency. Most importantly, applying our annealing technique to an LED exhibits a reasonably increased electroluminescence intensity associated with OMVPE-X, confirming that this site has a high excitation efficiency also under current injection. These results demonstrate the importance of OMVPE-X as a notable luminescent site for brighter and more efficient GaN:Eu,O-based LEDs.

Analytical crystal-field models applied to compounds doped with Eu3+

The point charge electrostatic model (PCEM) and the simple overlap model (SOM), both purely analytical crystal field models, are being briefly revisited, in order to show the evolution of their application to Eu doped compounds. Calculations are made through the method of equivalent nearest neighbours (MENN), and applied to the Eu(dipivaloylmethanate)31,10-phenanthroline [Eu(DPM)3o-phen] complex, with the aim of discussing the Eu–O and Eu–N interactions. The charge of the Eu ion is calculated using the Batista-Longo improved model (BLIM) to give gBLIM = 3,64e around the Eu-NN midpoint. The 7F1 crystal-field levels and level splitting were satisfactorily reproduced with two charge factors, namely, g1 = 0.495 and g2 = 0.415, assuming the luminescent site in a tetragonal point symmetry slightly distorted. In particular, it is shown that the Eu3+, itself, is satisfied by attracting an amount of charge, which neutralize/stabilize its own site electrostatically, no matter what the ligating ions are. The Eu-NN overlap (ρ = <4f|2s2p>) is assumed to be 0.1, which is physically plausible both as a limit in respect to β, the SOM correction factor to the PCEM, and describes the covalent contribution to the Ln-NN interaction, the latter is the most important contribution of the SOM to the crystal-field theory of lanthanide containing compounds. An eloquent comparison with crystal-field levels of the Eu:LiYF4 and Eu(btfa)3(4,4-bipy)(EtOH) is made. Finally, this paper is, indeed, a very simple tribute to Professor Oscar L. Malta, as an acknowledgement of his deep contribution to the author's apprenticeship about crystal-field theory of systems containing lanthanides.

Cation defects succeed in triggering super stability of narrow-band blue-emitting phosphors Ca3Sc2Si3O12: Bi3+ for backlighting display application

High-performance white light-emitting diodes (WLEDs) used for backlighting display applications require innovative and thermally stable narrow-band emission phosphors, particularly non-rare-earth Bi3+-activated phosphors. In this study, we demonstrate a defect-engineering strategy to create novel anti-thermal quenching phosphors Ca3Sc2Si3O12: xBi3+ (CSSO: xBi3+). Through structure refinement of CSSO: 0.06Bi3+ phosphor, we found that Bi occupies both Ca and Sc sites in the CSSO lattice. Direct visualization of atomic-resolution TEM and thermoluminescence spectra confirmed the formation of point defects due to the non-equivalent substitution of Ca2+ for Bi3+. Fluorescent-decay analysis revealed that two luminescence sites contribute to the blue-emitting of CSSO:Bi3+ phosphors. CSSO: 0.06Bi3+ phosphor exhibits outstanding thermal stability, with an integrated emission intensity of 103.6% at 423 K compared to that at 298 K. However, the addition of Li or Na as charge compensators reduced cationic defects, leading to a decrease in thermal stability. We believe that VCa″ defects are primarily responsible for the anti-thermal quenching behavior of CSSO: xBi3+ phosphors. An optimized CSSO: 0.06Bi3+ phosphor-based WLED displays a high color rendering index (CRI) of 90 and a wide color gamut (90% National Television System Committee (NTSC) standard), indicating its potential for use in industrial applications as a backlighting display.

Enhanced light output of Eu, O-codoped GaN caused by reconfiguration of luminescent sites during post-growth thermal annealing

Luminescence efficiency of Eu-related emission from Eu, O-codoped GaN (GaN:Eu, O) strongly depends on the local structure of Eu ions. Growth at relatively low temperature (∼960 °C) not only enables high Eu doping concentration but also elevates Eu-clustering due to its low diffusion coefficient, which results in formation of a large number of inefficient luminescent sites. We have studied the impact of post-growth thermal annealing at high temperatures on elimination of Eu clusters by photoluminescence measurements. These clarify that thermal annealing at high temperatures induces changes in the structural conformation and converts inefficient luminescent sites to efficient ones. As a result, the sample annealed at 1100 °C shows increased luminescence efficiency with a maximum of 5.1 times that of the as-grown sample. Post-growth thermal annealing offers a way to improve the efficiency of GaN:Eu, O further for practical application in III-nitride-based monolithic three-primary colors' light-emitting diodes.

Systematical site investigation and temperature sensing in Pr3+-doped M3RE4O9 (M = Sr and Ba; RE = Sc, Y, Lu)

Site engineering is an important modulation strategy for adjusting the physicochemical properties of lanthanide luminescent ions and shows growing applications in the optoelectronic field. Herein, we explored the influence of changing M2+ (or RE3+) ions on the occupation preference of Pr3+ ions and related crystal-field splittings in Pr3+:M3RE4O9 (M = Sr and Ba; RE = Sc, Y, Lu). The obtained results indicated that Pr3+ ions possess two kinds of doping sites (M2+ (Site Ⅰ) and RE3+ (Site Ⅱ)) in Pr3+:Ba3Lu4O9 and Pr3+:Ba3Y4O9, while only occupying Site Ⅰ in Pr3+:Sr3Sc4O9 and Pr3+:Ba3Sc4O9. The variation of RE3+ ions has little impact on the crystal-field splitting of both the two types of Pr3+ luminescent sites, and by contrast, replacing M2+ ones influences the energy-level splitting of the 3H4 multiplet of Site Ⅰ obviously. Moreover, we found that the host emission of M3RE4O9 stemming from intrinsic oxygen defects shows an apparent thermally induced fluorescence quenching phenomenon. And based on the defect and Site Ⅱ emissions, both Pr3+:Ba3Lu4O9 and Pr3+:Ba3Y4O9 exhibit excellent temperature sensing performance, yielding maximum relative sensitivity (Sr) of 8.40%·K−1 (132K) and 7.89%·K−1 (129K), respectively. This work enriches the site engineering strategy in Pr3+-based optical functional materials and broadens the relevant application in temperature sensing.

Impact of Sc3+-Modified Local Site Symmetries on Er3+ Ion Upconversion Luminescence in Y2O3 Nanoparticles.

Rare earth (RE) doped yttria sesquioxide has been widely used as host materials for upconversion (UC) phosphors due to their high refractive index, wide band gap, and high melting point. Meanwhile, while fluoride matrices with low phonon cutoff energies exhibit stronger UC emissions, RE-doped oxides exhibit better thermal stability and higher thermal sensitivity when applied as optical temperature sensors. In this work, Sc3+ is substituted in RE-doped Y2O3 lattices to generate smaller cation sites, enhancing the crystal field and modifying the allowed optical transitions. Er3+ is used as a photoluminescent probe to study the effect of site position and symmetry on the UC performance. In comparison with the traditional hydrothermal method, Sc3+ is successfully incorporated into the Y2O3 lattice via the co-precipitation/molten salt method without segregating observed. The Judd–Ofelt analysis was applied to determine the local symmetry and efficiency changes. Sc was found to be able to improve the luminescence performances of Er in Y2–xScxO3 (YScO) hosts by adjusting the local symmetry level around the luminescent sites. The local symmetry level was reduced with less than 30 mol % of Sc doping concentration based on the changes in Ω2 values. Meanwhile, the YScO oxide was found to significantly improve the luminescence intensity and red-to-green ratio at a lower Yb3+ concentration (5 mol %) instead of a higher concentration (20 mol %) commonly used. This was attributed to an increased energy transfer between the closer Yb3+–Er3+ pairs. Overall, this work allows the spatial occupancy of luminescence centers in the metal oxide host materials to optimize the UC luminescence performance and develop a high-efficiency oxide material for high-temperature applications such as optical thermometry.

Time‐Resolved X‐Ray Spectroscopy to Study Luminophores with Relevance for OLEDs

AbstractOrganic light‐emitting diodes (OLEDs) are employed in innovative display technologies and have the potential to be used widely in large area lighting. Luminophores containing 4d or 5d metals are efficient in electro‐luminescent devices due to their phosphorescent properties but are scarce and expensive. Alternatives take advantage of temperature‐activated delayed fluorescence (TADF), e. g. in Cu(I) complexes. We show modern X‐ray spectroscopy methods exemplified on Ru, Ir and Cu‐based luminophores offering insight into the capabilities of such techniques to researchers from various fields. Knowledge of structural rearrangements in the excited state is crucial to understand non‐radiative energy losses and to develop efficient luminophores. Pump‐probe X‐ray absorption spectroscopy (XAS) gives information about the molecular structure in the excited state and the electronic structure. We show how this information can be complemented with X‐ray emission spectroscopy at X‐ray free‐electron lasers (XFEL) and discuss the potential of time‐resolved X‐ray excited optical luminescence (TR‐XEOL) to provide additional selectivity of XAS to luminescent sites.

Ultra-wideband phosphor Mg2Gd8(SiO4)6O2:Ce3+,Mn2+: Energy transfer and pressure-driven color tuning for potential applications in LEDs and pressure sensors

Energy transfer and pressure-driven color tuning phosphor Mg2Gd8(SiO4)6O2:Ce3+ (MGS:Ce3+), with ultra-wideband spectra was synthesized by high-temperature solid-state method. When the phosphor was excited by ultraviolet light, it emitted a sort of cold near-white light. The photoluminescence emission (PL) and excitation (PLE) spectra, luminescence sites of MGS:Ce3+ had been researched. In order to adjust the light color to achieve the purpose of spectral tuning, two methods had been implemented. The first method was doping Mn2+ into MGS:Ce3+. There was energy transfer from Ce3+ to Mn2+ in such phosphor, and the energy transfer had been researched in detail. After doping with Mn2+, the color coordinates positions and correlated color temperature (CCT) of phosphors were improved obviously. When fixed the concentration of Ce3+ and the doping concentration of Mn2+ is y = 1.0, 2.0 and 3.0, the phosphor can realize the warm white light emission. The second one was applying pressure to MGS:Ce3+, expecting to achieve the above purpose through the red shift of the spectrum. The results showed that the sample could withstand the high pressure of 26.03 GPa. A relatively rare phenomenon of pressure enhancement emission appeared when the pressure was between atmospheric pressure and 3.17 GPa. When the pressure exceeded 3.17 GPa, the luminescence intensity decreased regularly with the increase of pressure and the phosphor showed high pressure sensitivity (dλ / dP ≈ 1.8453 nm GPa−1). What’s more, the sample at compression environment made a significant red-shift about 60 nm of the emission bands. In the process of compression, the color coordinate shows that the light color of phosphor can be adjusted from blue-green light to yellow light region under the excitation of 355 nm. All above results revealed that the convenient synthetic method, effective light color coordinating made the MGS:Ce3+ and MGS:Ce3+,Mn2+ become a potential phosphor for (warm) white light. What’s more, the emission spectra red shift resulting from pressure change made it possible to be a potential optical pressure sensor.

Novel Photoluminescent Gold Complexes Prepared at Octanethiol–Water Interfaces: Control of Optical Properties by Addition of Silver Ions

Abstract Octanethiol (C8-SH) was shaken with an aqueous solution containing Au(III) and/or Ag(I) ions. The C8-SH molecules reacted with the Au(III) ions to form red-luminescent Au thiolates. The addition of silver ions generated blue-luminescent species, and red-luminescent species also formed in the reaction solution. The blue-luminescent species contained gold–silver (AuAg) bimetallic thiolate complexes. Increasing the silver fraction resulted in higher yields of the blue-luminescent species, but the spectral properties of the two kinds of complexes were almost independent of the silver fraction. X-ray photoelectron spectroscopy (XPS) indicated that the complexes contained metal gold (Au(0)) and silver ions (Ag(I)). The addition of thiol-terminated poly(ethylene oxide) (mPEG-SH) assisted the dialysis of the blue-luminescent complexes. Transmission electron microscope (TEM) investigations revealed the presence of metallic complexes (5 nm) and complex aggregates (50–200 nm). Luminescent sites, which were bimetallic sites containing gold and silver atoms, were formed in the complexes.

Spectroscopic study of the Eu3+ local symmetry in EuF3 crystal

We employed the simple overlap model (SOM) with the method of equivalent nearest neighbours (MENN) to indicate the local symmetry of the Eu3+ in the europium trifluoride (EuF3) compound through two analyses based on the emission spectra. In first situation, three lines were observed at the 5D0 → 7F1 (0-1) transition. Therefore, based on the amount of non-null crystal field parameters, we indicate that the Eu ion occupies a site with distorted inversion centre as a combination of C2 and C2h symmetries, with the following charge factors: g1 = 0.438, g2 = 0.292, g3 = 0.411, g4 = 0.201, g5 = 0.396 and g6 = 0.293. In second situation, with two lines at the 0-1 transition, we suggested the luminescent site as a combination of the D3d and D3h symmetries with g1 = 0.279 and g2 = 0.495. The 7F1 manifold splitting was obtained through Auzel-Malta equation. All theoretical calculations reproduced satisfactorily the 7F1, 7F2 and 5D1 energy sublevels in good agreement with experimentals data.

High partial thermal conductivity of luminescence sites: a crucial factor for reducing the heat-induced lowering of the luminescence efficiency

The high partial thermal conductivity of luminescence sites is associated with the reduction of the heat-induced lowering of the luminescence efficiency of phosphors. This finding may be helpful for screening efficient phosphors.

Computational simulation and crystal field analysis of the Eu3+-doped LiF

The local symmetry of the Eu3+ was obtained through atomistic simulation and crystal field models applied to lanthanides. Structural properties such as lattice parameters and unit cell volume were reproduced using a set of empirical interatomic potentials with good accuracy. The LiF Anti-Schottky intrinsic defect was most favourable energetically. The solution energy obtained by bound extrinsic defects showed that the Eu3+ prefers the Li+ site compensated by lithium vacancy. Spectroscopic calculations revealed that the europium occupies a luminescent site with distorted inversion centre. A slightly distorted D4h symmetry is most favourable with the charge factors: g1 = 0.629, g2 = 0.738, g3 = 0.627 and g4 = 0.625, which reproduced satisfactorily the 7F1 manifold splitting and the 7F1, 7F2 and 5D1 energy sublevels.

Luminescence sites and spectra of metal doped microwave synthesized Mg2SiO4:Tb

Terbium doped magnesium orthosilicate (Mg2SiO4: Tb) has been reported as the most efficient thermoluminescence dosimeter material. Further sensitivity improvements of Mg2SiO4: Tb may be achieved by co-doping with other metal ions. Performance is strongly influenced by the sintering conditions, as shown here for Mg2SiO4: Tb samples which were synthesized with microwave thermal processing. A series of Mg2SiO4: x mol% Tb (x = 0.5, 1, 3, 5, 7) and Mg2SiO4: Tb, M (M = Li, Na, Ca, Al, Ga) samples are compared. Photoluminescence (PL) and Thermoluminescence (TL) of all samples are dominated by the characteristic emission of Tb3+. Co-doping can improve the sensitivity, and this is linked to modification of the micro-structure, as revealed by SEM measurements. Among the co-doped samples investigated, Mg2SiO4: Tb, Na shows the highest TL response with the main TL peak at 196oC. Differences between processing with microwave heating and thermal sintering are apparent in terms of the association of the dopants. Benefits and future possibilities with wider applications are discussed.

Atomistic simulation and spectroscopic study of the [formula omitted] doped [formula omitted] crystal

The CaSO4:Eu3+ has been prepared by the slow evaporation route with different concentrations of the luminescent ion, characterized by XRD and emission spectra techniques and studied by atomistic simulation and crystal field theory. The lattice parameters were obtained with a new set of potentials which is proving to be more appropriate to simulate the lattice parameters and the local Eu3+ luminescent site than those published elsewhere. The Simple Overlap Model (SOM) was applied in the frame of the Method of Equivalent Nearest Neighbours (MENN) in order to predict the charge factors devoted do the Eu–O bond and the 7F1 energy sub-levels through the crystal field parameters. The central ion charge (gEu) was predicted by the Batista–Longo Improved Model (BLIM). Our calculations indicated that the Eu3+ prefers the Ca2+ site compensated by calcium vacancy or interstitial oxygen. Using the four simulated structures the 7F1 Stark levels were satisfactory reproduced. Thus, based on the simulations and the number of lines exhibited in the emission spectra, one has a strong indication that the Eu ion occupies a distorted local symmetry which is a combination of the D2 and C2v point groups.

Critical role of defect states on visible luminescence from ZnS nanostructures doped with Au, Mn and Ga

In this paper, we present the effect of various self doping of catalysts (Au, Mn, and Ga) on the emission properties of cubic ZnS nanostructures. The solubility of the catalysts during the growth was confirmed by FESEM, HRTEM, and XRD. XPS confirmed the formation and variation of intrinsic defects like S, Zn vacancies and extrinsic defects created by self-doped catalysts, which varied with the type of catalysts. The luminescence properties of ZnS nanostructures showed strong dependence on the type of catalyst related defects. Low temperature PL spectroscopy showed that the Au created shallow surface defects states (~100 meV from the conduction band, and Ga induced shallow level defect states with emission in the UV ~360 meV). The temperature dependent PL spectroscopy showed strong negative thermal quenching of PL intensity of blue and orange emission in Au catalyzed ZnS nanostructures while Mn and Ga showed quenching behavior only in yellow and blue bands emission, respectively. Time-resolved PL spectra obtained from all nanostructures demonstrated two time decay constants. The percentage contributions of the fast decay (direct recombination of electrons and holes) and slow decay (trapped electrons at the luminescent sites) were determined for three catalyzed ZnS nanostructures. The percentage contributions and long life time components of blue and green bands were high in Au catalyzed ZnS nanostructures, compared to Mn and Ga catalyzed ZnS nanostructures. Present results indicate the potential use in a broad spectrum tunable nanolasers and multi-color light source.

Theoretical spectroscopic investigation of the Eu3+ local symmetry in LiF through crystal field models

We employed the simple overlap model (SOM) with the method of equivalent nearest neighbours (MENN) in the Auzel-Malta equation and in the energy sublevels equations to investigate the local symmetry of the Eu3+ in the LiF crystal and predict the 7F1, 7F2 and 5D1 energy sublevels. The Batista-Longo Improved Model (BLIM) was helpful to predict the Eu3+ ion charge and establish the Eu–F interaction charge position considering the covalence on the chemical bonding by the Brik-Avram overlap integrals matching with the octet rule. The LiF:Eu3+ were studied elsewhere in two situations. In the first case, the Eu3+ occupies a site without inversion centre because the 5D0 – 7F2 (0-2) transition is more intense than 5D0 – 7F1 (0-1) transition, which we indicate spectral behaviour of the a α-EuF3 polymorphic phase. Thus, with a combination of non-null crystal field parameters, we obtained the luminescent site as being a distorted C2v symmetry with charge factors g1 = 0.485, g2 = 0.499, g3 = 0.403, g4 = 0.343 and g5 = 0.257. This set of charge factors reproduced the 7F1 manifold in good agreement with experimental data. In the second case, with the 0-1 transition more intense than the 0-2 transition, we have the indication which the Eu3+ occupies a site with distorted inversion centre. Furthermore, due to the asymmetry of the peaks, we performed a deconvolution of these peaks with two lines in both 7F1 and 7F2 manifolds. Assuming the distorted luminescent site have being D4h or D4d symmetries with g = 0.383 and D2d symmetry with g1 = 0.400 and g2 = 0.396, we have reproduced satisfactory the 7F1 level splitting and 7F2 and 5D1 sublevel positions, considering the Eu3+ octacoordinated.

Multi-site tunable emission of Eu2+ ions in Ca10Na(PO4)7 host

In this paper, three types of Eu2+ luminescent centers with emission bands at 407, 473, and 583 nm were found in the Ca10Na(PO4)7 phosphors with a β-Ca3(PO4)2-type structure. The relationship between the luminescent centers and metal sites was determined by the Rietveld refinements and photoluminescence spectral analysis. The concentration quenching behavior and the temperature dependent luminescence properties of Ca10Na(PO4)7:Eu2+ phosphors were investigated. The emission color and chromaticity coordinates of phosphors can be tuned by adjusting doping concentration and altering temperature.