Nearest-neighbor Ions Research Articles

Synthesis and photoluminescence properties of a novel red emitting Ba3ZnTa2O9: Eu3+ phosphor

A novel Ba3ZnTa2O9: xEu3+ (0 ≤ x ≤ 0.16) red luminescent material was composition via solid-state method. The phase purity, crystal three-dimensional structure, micromorphology, UV-Vis absorption spectra, photoluminescence performance, energy transfer mechanism among Eu3+ ions was studied in detail. The Ba3ZnTa2O9: xEu3+ phosphors effectively excited under 395 nm near ultraviolet wavelength and showed intense red emission at 594 nm, corresponds to the 5D0→7F1 transition of Eu3+. It obtained from experiments that the phosphors of Ba3ZnTa2O9: xEu3+ optimal doping concentration is x equal to 0.10. The critical distance of Eu3+ ions is 15.77Å, and the non-radiative energy transfer between Eu3+ ions is mainly affected by nearest-neighbor ions. Thermal stability of Ba3ZnTa2O9: 0.1Eu3+phosphors was determined by the emission spectrum associated with temperature. The chrominance coordinates of Ba3ZnTa2O9: 0.1Eu3+ phosphors located at (0.5367, 0.4497). Owing to Ba3ZnTa2O9: xEu3+ phosphors has high color purity, illustrating it has potential application value in commercial red phosphors.

Nd3+ concentration effect on luminescent properties of MgAl2O4 nanopowders synthesized by modified Pechini method

In this paper, the concentration series of MgAl2O4:Nd3+ nanocrystalline powders have been synthesized by modified Pechini method. Neodymium doping concentration was varied within range of 0.05–5 ​at.%. The obtained samples have been analyzed using the various experimental methods: X-Ray diffraction, scanning electron microscopy, energy dispersive X-Ray spectroscopy, as well as steady-state and kinetics photoluminescence spectroscopy. According to XRD, all synthesized samples are monophasic without any structural impurities. The doping concentration effect on the luminescent characteristics of MgAl2O4:Nd3+ nanocrystalline particles has been studied in terms of emission intensity and lifetime. The optimal doping Nd3+ concentration was determined to be 0.1 ​at.%. Concentration quenching in MgAl2O4:Nd3+ powders occurred via energy transfer among the nearest neighbor ions. Performed studies shed the light on behavior of Nd3+ ions in nanoscale magnesium aluminum spinel.

Double perovskite Ca2MgTeO6:Eu3+ red-emitting phosphors with high thermal stability for near UV/blue excited white LEDs

A series of Eu3+-doped double perovskite Ca2MgTeO6 (CMTO) red-emitting phosphors with high thermal stability were successfully prepared using the solid-state reaction at 1100 °C. The phase purity, surface morphology, and elemental mapping were investigated. Under near-ultraviolet (n-UV) (398 nm) and blue light (465 nm) excitation, the phosphors showed the strongest emission peak at 616 nm belonging to 5D0→7F2 transition. Besides, the ideal Eu3+ doping concentration was 0.30 mol. The major reason for the concentration quenching was the nearest neighbor ions interaction. More importantly, the CMTO:Eu3+ phosphors showed excellent thermal stability with a high value of activation energy (0.29 eV). The color purity of CMTO:0.30Eu3+ phosphor was up to 99.9% and the internal quantum efficiency (IQE) of CMTO:0.30Eu3+ was measured to be 53%. White light-emitting diodes (w-LEDs) based on the InGaN chip (λ = 398 nm) and GaN chip (λ = 465 nm) with high color rendering index (Ra) and low correlated color temperature (CCT) have been fabricated. Hence, the double perovskite CMTO:Eu3+ red phosphors have potential applications in the illumination field.

Tm3+-Dy3+-Eu3+ tri-doped transparent glass-ceramics containing NaY(MoO4)2 crystal phase: Preparation, energy transfer, warm white light emitting

Tm3+-Dy3+ co-doped and Tm3+-Dy3+-Eu3+ tri-doped glass-ceramics (dGCs) containing NaY(MoO4)2 crystal phase were prepared. The crystal phase of the GCs was determined to be NaY(MoO4)2 by XRD, and the optimal heat treatment condition of GCs was determined to be 670 °C/2.5 h by DSC, SEM, and transmittance curves. Under 362 nm light excitation, the chromaticity coordinates of the Tm3+-Dy3+ co-doped GCs were tuned from blue to white region by adjusting the Dy3+ concentration. The energy transfer (ET) mechanism from Tm3+ to Dy3+ was a dipole-dipole interaction, and the ET efficiency was as high as 56.3% when the concentration of Dy3+ was 1.1%. When the concentration of Dy3+ exceeds 1.1%, concentration quenching caused by interaction between nearest-neighbor ions can be observed. With the addition of Eu3+, the chromaticity coordinates shifted from cool white to warm white region. These GCs were expected to be used in white LEDs.

Europium (III) doped LiNa2B5P2O14 phosphor: Surface analysis, DFT calculations and luminescent properties

Borophosphate-based phosphors activated by rare earth ions have received considerable attention for their potential in solid-state lighting, owing to their numerous crystalline environments, low synthetic cost, and environmental friendliness of the borophosphate host. Herein, we report the solid-state synthesis of a new europium-activated borophosphate LiNa2B5P2O14 (LNBPO) phosphor. The association between doping europium content and luminescent behavior is studied. For reddish-orange emission of LNBPO:Eu3+, an europium content of 7 mol% yields the best performance. The quenching mechanism arises from the energy transfer among the nearest-neighbor europium ions. Detailed investigation of 5D0 → 7F0 (579 nm), 5D0 → 7F1 (588 and 594 nm), and 5D0 → 7F2 (613, 616 and 621 nm) transitions identifies the crystallographic occupancy of Eu3+ ions and the resulting characteristics. The chromatic properties, correlated colour temperature (CCT), colour purity (CP), internal quantum efficiency (IQE), and fluorescence decay reveal that LNBPO-based reddish-orange phosphor activated with trivalent europium is potentially useful in warm white LEDs fabricated by a near ultraviolet LED chip.

Crystal structure refinement, photoluminescence properties and energy transfer of multicolor tunable Ca2Al2SiO7:Tm3+, Dy3+ for NUV white-light-emitting diodes.

A promising phosphors Ca2Al2SiO7:Tm3+,Dy3+ were synthesized by conventional high temperature sintering. Phase identification, crystal structure refinement, luminescence properties, energy transfer mechanism of Tm3+→Dy3+, and CIE color coordinates were investigated systematically. The phase structure of prepared phosphors were confirmed by XRD analysis and structure refinement. From the results of photoluminescence, the CASO: Tm3+ phosphors showed intense blue light emission peaks at 454nm (the transition from 1D2 to 3F4), while CASO:Dy3+ phosphors exhibited predominant yellow light emission peaks at 581nm (the transition from 4F9/2 to 6H13/2), implying that the Dy3+ were located in the non-inverted symmetric site of the CASO host lattice. Meanwhile, the results exhibited that the optimal doping content of Dy3+ was 0.01, and the mechanism of concentration quenching was the nearest-neighbor ions interaction. The overlapped emission (Tm3+)/excitation (Dy3+) spectra, decay curves and the energy level scheme about CASO:Tm3+,Dy3+ confirmed the energy transfer of Tm3+→Dy3+. Moreover, by adjusting Tm3+/Dy3+ ions concentration, the intensities of yellow emission for Dy3+ and blue emission for Tm3+ could be adjusted to tune the emitting color of CASO:Tm3+, Dy3+. Excited by the most effective excitation wavelength at 355nm, the CIE coordinates (0.3422, 0.3262) of phosphor CASO:0.01Tm3+, 0.01Dy3+ was closest to the coordinates of white chromaticity (0.33, 0.33). Results indicate that the potential value of phosphors Ca2Al2SiO7:Tm3+,Dy3+ are used as a single-phase color-adjustable phosphors for NUV pumped white-LEDs.

Low-temperature solid-state synthesis and luminescent performance of a novel Li2NaBP2O8-based phosphor activated with europium (III)

For the application of inorganic phosphors in solid-state lighting field, exploring a synthesis route with low energy consumption and low cost is the current research focus. In this study, a low-temperature solid-state synthesis route for a novel Li2NaBP2O8:Eu3+ (LNBP:Eu) phosphor is reported. The phase structure, morphology, and elemental composition of its powder phase are characterized. According to photoluminescence and X-ray photoelectron spectroscopy data, the occupancy site and oxidation state of doping europium are discussed. Under near-UV (395 nm) excitation, the powder phase exhibits reddish-orange emission with a dominant 5D0 → 7F1 transition of europium. The intensity of visible photoluminescence is closely influenced by the europium doping content. The optimal content is 0.04 mol, and concentration quenching is ascribed to energy transfer among the nearest-neighbor europium ions. Moreover, chromatic properties are investigated in detail. The obtained data show that the LNBP:Eu powder phase is a prospective phosphor for application in near-UV-converted warm white light-emitting diodes.

Luminescence properties of GdOCl:Eu3+ red-emitting phosphors for white light-emitting diodes

The structural and photoluminescence properties of Eu3+ activated GdOCl red-emitting phosphors were investigated. All the GdOCl:xEu3+ (x = 0–0.125) phosphors are crystallized in the tetragonal PbFCl-type structure (P4/nmm space group). Under the 289 nm excitation, all the phosphors show bright red emissions which are originated from the 5D0→7FJ (0 ≤J ≤ 4) transitions of Eu3+. The GdOCl:0.075Eu3+ phosphor presents the strongest emission intensity, and concentration quenching phenomenon dominated by the nearest-neighbor ions interaction appears as x exceeds 0.075. The color purity and quantum efficiency (under 289 nm excitation) for GdOCl:0.075Eu3+ phosphor reach 92% and 68.7%, respectively, which are comparable or even better than some of the commercialized red-emitting phosphors. Furthermore, the emission intensity at 423 K reaches ~56.1% of that at 303 K for GdOCl:0.075Eu3+ phosphor, such good thermal stability is due to the relative high activation energy (0.18 eV). The present results indicate that the GdOCl:0.075Eu3+ phosphor is a competitive candidate for white light-emitting diodes applications.

A novel orange–red emitting phosphor Sr2LuTaO6:Sm3+ for WLEDs

A novel double perovskite tantalite orange–red light emitting Sr2LuTaO6:Sm3+ phosphor was synthesized by the solid state reaction. The phase, crystal structure, photoluminescence properties, thermal stability and decay curves were studied. The X-ray diffraction patterns indicated that the phosphor has a pure phase of cubic phase structure. Excited by near-ultraviolet light at 407 nm, the sample exhibited three sharp emission peaks at 564 nm, 600 nm, 645 nm corresponding to the 4G5/2 → 6HJ (J = 5/2, 7/2 and 9/2) transitions, respectively. The optimum doping concentration of Sm3+ ions was determined to be 5 mol% and the concentration quenching process comes from the energy transfer among nearest-neighbor ions. The as-prepared phosphors showed excellent thermal stability, the integral intensity at 423 K is about 91.10% of the initial intensity. The CIE chromaticity coordinates of Sr2LuTaO6:Sm3+ phosphors located in orange–red region. The results suggest that Sr2LuTaO6:Sm3+ phosphors have great potential application in white light-emitting diodes.

Self-template construction of honeycomb-like mesoporous YPO4:Ln3+ (Ln = Eu, Tb) phosphors with tuneable luminescent properties

Rare earth (RE)-based phosphors with mesoporous structure that can improve the absorption and utilization of light have attracted much attention recently. Herein, we develop a novel and facile self-template strategy to synthesize honeycomb-like mesoporous YPO4:Ln3+ (Ln = Eu, Tb) phosphors using Y4O(OH)9NO3: Ln3+ as the precursor through a simple H3PO4 etching process. The maximum specific surface area of the mesoporous YPO4:Ln3+ phosphors can reach 406 m2 g−1. The influence of mesoporous structure, crystallinity, and the concentration of rare earth ions on the photoluminescence performance of mesoporous YPO4:Ln3+ phosphors was investigated. The results of fluorescence measurements indicate the mesoporous YPO4:Ln3+ phosphors exhibit better photoluminescence performance after calcination at 900 °C due to the large surface area and high crystallinity. The optimum doped concentrations of Eu3+ ions and Tb3+ ions are 0.12 and 0.08, respectively, and the concentration quenching occurs among nearest-neighbor ions. This work provide a new sight on preparation of phosphors for white light-emitting diodes lamps.

Luminescence properties of Eu3+ ions doped in novel host materials Sr9R(PO4)7 (R = In, Ga)

Novel Sr9R(PO4)7 (R = In, Ga) host materials for Eu3+ - doped phosphors were synthesized by a high-temperature solid-state reaction method. The crystal structure, luminescence properties and thermal stability of the phosphors were explored. The phase analysis indicated that the phosphors crystallized in monoclinic structure, the emission spectra of both In and Ga containing phosphors were mainly composed of two sharp peaks centered at about 591 and 617 nm, corresponding to the 5D0→7F1 and 5D0→7F2 transitions of Eu3+ ions. While, the relative emission and excitation intensities of Sr9In(PO4)7: Eu3+ were weaker than Sr9Ga(PO4)7: Eu3+. Moreover, the energy transfer mechanism among Eu3+ ions in the phosphors depended upon energy transfer among the nearest-neighbor ions described by the Dexter theory. The selected Sr9In(PO4)7: 0.06Eu3+ and Sr9Ga(PO4)7: 0.06Eu3+ exhibited high thermal stability and the chromaticity coordinate of the phosphors were located in the red-orange light region.

A novel synthesis route to monodisperse Na5Lu9F32:Tb3+ phosphors with superior thermal stability

Nanocrystalline Tb3+-doped Na5Lu9F32 powders were prepared by a facile and environmentally-friendly hydrothermal process for the first time. Upon excitation at 368 nm, the Na5Lu9F32:Tb3+ nanocrystals show the characteristic f-f emissions and gives strong green emission. Furthermore, the optimum doping concentration of the Tb3+ is 7 mol% and its lifetime value is 10.227 ms. Compared with the strong absorbed exciting radiation (at 368 nm), the weak absorbed exciting radiation (at 317 nm) can be used to explore the mechanism of concentration quenching and the concentration quenching was demonstrated to occur among nearest-neighbor ions. The temperature-dependent PL spectra suggested that the products possessed good thermal stability and the activation energy was found to be 0.14 eV. These results show this green-emitting phosphors material may have potential applications in w-LEDs.

High quantum efficiency red-emitting K2Gd(PO4)(WO4): Sm3+ phosphor: preparation, characterization and photoluminescence properties

The Sm3+-activated K2Gd(PO4)(WO4) phosphors were prepared by a high temperature solid state reaction in air atmosphere and their photoluminescence properties were investigated in detail. These phosphors manifest the intense absorption under the 404 nm and give rise to bright red luminescence at the main emission peaks of 568, 604, 649 and 708 nm, corresponding to the 4G5/2→6HJ/2 (J = 5, 7, 9, 11) transitions of Sm3+ ions, respectively. The type of energy transfer between Sm3+ ions were affirmed as among nearest-neighbor ions and the critical distance Rc of concentration quenching was calculated to be 27.23 A. Furthermore, K2Gd0.98(PO4)(WO4):0.02Sm3+ was provided with superb color coordinate (0.5806, 0.4164) also high color purity. Temperature related photoluminescence spectra and decay curves indicated that the K2Gd0.98(PO4)(WO4):0.02Sm3+ possessed good thermal stability and quantum efficiency was determined to be 91.2%. These remarkable features revealed that the K2Gd(PO4)(WO4):Sm3+ phosphors are high-performance phosphors for applications of white light-emitting diodes.

Molecular ionization of chloromethane in strong fields: nearest neighbor gateway to highly charged ions

The strong and ultrastrong field-molecule interaction is a complex, many-body process involving multiple ionization processes. We present ion yields and molecular fragment energies for the ionization of chloromethane (CH3Cl) in a laser field with intensities spanning from 1014 to 1017 W cm−2. As the laser intensity increases, ionization of CH3Cl is observed to pass from molecular tunneling, to enhanced ionization (EI), to an atomic-like response. The energy spectra of the ions show no dependence on the intensity and has its source in dissociative molecular ionization. A classical model of an aligned C–Cl ion is used to model the interaction. Following an initial molecular ionization process, our results show EI is a driving influence in the formation of low charge states until ionization become atomic-like and involves tightly bound ion states whose ionization is unaffected by nearest neighbor ions of similar ion charge.

Weak doping dependence of the antiferromagnetic coupling between nearest-neighbor Mn2+ spins in (Ba1−xKx)(Zn1−yMny)2As2

Dilute magnetic semiconductors (DMS) are nonmagnetic semiconductors doped with magnetic transition metals. The recently discovered DMS material (Ba$_{1-x}$K$_{x}$)(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ offers a unique and versatile control of the Curie temperature, $T_{\mathrm{C}}$, by decoupling the spin (Mn$^{2+}$, $S=5/2$) and charge (K$^{+}$) doping in different crystallographic layers. In an attempt to describe from first-principles calculations the role of hole doping in stabilizing ferromagnetic order, it was recently suggested that the antiferromagnetic exchange coupling $J$ between the nearest-neighbor Mn ions would experience a nearly twofold suppression upon doping 20\% of holes by potassium substitution. At the same time, further-neighbor interactions become increasingly ferromagnetic upon doping, leading to a rapid increase of $T_{\mathrm{C}}$. Using inelastic neutron scattering, we have observed a localized magnetic excitation at about 13 meV, associated with the destruction of the nearest-neighbor Mn-Mn singlet ground state. Hole doping results in a notable broadening of this peak, evidencing significant particle-hole damping, but with only a minor change in the peak position. We argue that this unexpected result can be explained by a combined effect of superexchange and double-exchange interactions.

Eu2+-doped Ba2GaB4O9Cl blue-emitting phosphor with high color purity for near-UV-pumped white light-emitting diodes

Eu2+-doped borate fluoride Ba2GaB4O9Cl was synthesized by the conventional high-temperature solid-state reaction. The crystal structure and luminescence properties of the phosphors, as well as their thermal luminescence quenching capabilities and CIE chromaticity coordinates were systematically investigated. Under the excitation at 340nm, the phosphor exhibited an asymmetric broad-band blue emission with a peak at 445nm, which is ascribed to the 4f–5d transition of Eu2+. It was further proved that energy transfer among the nearest neighbor ions is the major mechanism for concentration quenching of Eu2+ in Ba2−xGaB4O9Cl:xEu2+ phosphors. The luminescence quenching temperature is 432K. The CIE color coordinates are very close to those of BaMgAl10O17:Eu2+ (BAM). All the properties indicated that the blue-emitting Ba2GaB4O9Cl:Eu2+ phosphor has potential application in white LEDs.

Preparation, crystal structure and photoluminescence properties of Ce3+ activated Ba3Y1−yLuyAl2O7.5 phosphors for near-UV LEDs

A series of novel blue-green broadband emitting phosphors Ba3Y1−yLuyAl2O7.5: Ce3+ (0⩽y⩽0.5) were synthesized via the solid state reaction. The crystal structure and the photoluminescence properties were investigated for the application in white light-emitting diodes. The phosphors have two Ba2+ sites and one Y(Lu)3+ site with different coordination environment. These phosphors show the good absorption ranging from the ultraviolet to the blue region, the emission spectra contain both blue and green compositions, and the peaks can shift from 478nm to 493nm by changing the doped Lu3+ concentration, the mechanisms and reasons of the changes of the PL/PLE spectra, fluorescence decay curves and thermal quenching properties have also been studied in detail. The critical distance for Ce3+ ions in the Ba3YAl2O7.5 host was calculated to be 23.85Å and the energy transfer mechanism occurs among the nearest-neighbor ions. The above results indicate that Ba3Y1−yLuyAl2O7.5: Ce3+ is a good candidate as the blue-green component for near-UV LEDs.

Dysprosium doped novel apatite-type white-emitting phosphor Ca9La(PO4)5(GeO4)F2 with satisfactory thermal properties for n-UV w-LEDs

A novel apatite structure phosphor Ca9La(PO4)5(GeO4)F2:Dy3+ (CLPGF:Dy3+) with a hexagonal lattice in the P63/m space group was synthesized via a facile solid state technique. The crystal and fine local structure as well as their photoluminescence properties were investigated in detail. The CLPGF:Dy3+ phosphor can absorb in the UV-vis spectral region of 290–475 nm and exhibit two intense emission bands centered at 485 and 580 nm, which ascribes to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+, respectively. The concentration quenching of Dy3+ emission occurs via the energy transfer among the nearest-neighbor ions and the corresponding quenching mechanism was verified to be the dipole-dipole interaction. The quantum efficiencies of the phosphors were examined to be 72.9% and its luminescence intensity at 150 °C decreases to 93.8% and 98.6% of the initial value at room temperature, which corresponds to 4F9/2 to 6H15/2 transition and 4F9/2 to 6H13/2 transition of Dy3+ ions, respectively. Their interesting photoluminescence properties indicate that the CLPGF:Dy3+ phosphor is a promising white-emitting candidate for w-LEDs applications.

Empirical electronic polarizabilities of ions for the prediction and interpretation of refractive indices: Oxides and oxysalts

An extensive set of refractive indices determined at λ = 589.3 nm ( n D ) from ~2600 measurements on 1200 minerals, 675 synthetic compounds, ~200 F-containing compounds, 65 Cl-containing compounds, 500 non-hydrogen-bonded hydroxyl-containing compounds, and ~175 moderately strong hydrogen-bonded hydroxyl-containing compounds and 35 minerals with very strong H-bonded hydroxides was used to obtain mean total polarizabilities. These data, using the Anderson-Eggleton relationship α T = ( n D 2 − 1 ) V m 4 π + ( 4 π 3 − c ) ( n D 2 − 1 ) where α T = the total polarizability of a mineral or compound, n D = the refractive index at λ = 589.3 nm, V m = molar volume in A 3 , and c = 2.26, in conjunction with the polarizability additivity rule and a least-squares procedure, were used to obtain 270 electronic polarizabilities for 76 cations in various coordinations, H 2 O, 5 H x O y species [(H 3 O) + , (H 5 O 2 ) + , (H 3 O 2 ) − , (H 4 O 4 ) 4− , (H 7 O 4 ) − ], NH 4 + , and 4 anions (F − , Cl − , OH − , O 2− ). Anion polarizabilities are a function of anion volume, V an , according to α − = α − 0 ⋅ 10 − N o / V an 1 . 20 where α − = anion polarizability, α − o = free-ion polarizability , and V an = anion molar volume. Cation polarizabilities depend on cation coordination according to a light-scattering (LS) model with the polarizability given by α ( C N ) = ( a 1 + a 2 C N e − a 3 C N ) − 1 where CN = number of nearest neighbor ions (cation-anion interactions), and a 1 , a 2 , and a 3 are refinable parameters. This expression allowed fitting polarizability values for Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Mn 2+ , Fe 2+ , Y 3+ , (Lu 3+ -La 3+ ), Zr 4+ , and Th 4+ . Compounds with: (1) structures containing lone-pair and uranyl ions; (2) sterically strained (SS) structures [e.g., Na 4.4 Ca 3.8 Si 6 O 18 (combeite), Δ = 6% and Ca 3 Mg 2 Si 2 O 8 (merwinite), Δ = 4%]; (3) corner-shared octahedral (CSO) network and chain structures such as perovskites, tungsten bronzes, and titanite-related structures [e.g., MTiO 3 (M = Ca, Sr, Ba), Δ = 9–12% and KNbO 3 , Δ = 10%]; (4) edge-shared Fe 3+ and Mn 3+ structures (ESO) such as goethite (FeOOH, Δ = 6%); and (5) compounds exhibiting fast-ion conductivity, showed systematic deviations between observed and calculated polarizabilities and thus were excluded from the regression analysis. The refinement for ~2600 polarizability values using 76 cation polarizabilities with values for Li + → Cs + , Ag + , Be 2+ → Ba 2+ , Mn 2+/3+ , Fe 2+/3+ , Co 2+ , Cu +/2+ , Zn 2+ , B 3+ → In 3+ , Fe 3+ , Cr 3+ , Sc 3+ , Y 3+ , Lu 3+ → La 3+ , C 4+ → Sn 4+ , Ti 3+/4+ , Zr 4+ , Hf 4+ , Th 4+ , V 5+ , Mo 6+ , and W 6+ in varying CN’s, yields a standard deviation of the least-squares fit of 0.27 (corresponding to an R 2 value of 0.9997) and no discrepancies between observed and calculated polarizabilities, Δ > 3%. Using n D = 4 π α ( 2 . 26 − 4 π 3 ) α + V m + 1 the mean refractive index can be calculated from the chemical composition and the polarizabilities of ions determined here. The calculated mean values of n D > for 54 common minerals and 650 minerals and synthetic compounds differ by In a comparison of polarizability analysis with 68 Gladstone-Dale compatibility index (CI) (Mandarino 1979, 1981) values rated as fair or poor, we find agreement in 32 instances. However, the remaining 36 examples show polarizability Δ values

A novel blue-emitting Ba5(BO3)2(B2O5):Ce3+ phosphor for application in near-UV white LEDs

The blue-emitting phosphor Ba5(BO3)2(B2O5):Ce3+ was synthesized by a high-temperature solid-state method. Its crystal structure, luminescence properties, concentration-quenching mechanism and thermal stability were investigated. This phosphor can be effectively excited by 351-nm near-ultraviolet light, with a broad blue emission band. The emission spectra of the Ba5(BO3)2(B2O5):Ce3+ phosphor were clearly monitored with critical emission quenching as a function of the Ce3+ content. It was further proven that the energy transfer among the nearest-neighbor ions results in the concentration quenching of Ce3+ in Ba5(BO3)2(B2O5). The dependence of the luminescent intensity on the charge-compensated (Li+, Na+, K+) was also discussed. Ba5(BO3)2(B2O5):Ce3+ phosphors can be effectively excited by near-UV light and simultaneously exhibit excellent luminescence resistibility against thermal quenching in the temperature range from 300 to 400 K. The activation energy ΔE is calculated to be 0.21 eV. The present work suggests that the Ba5(BO3)2(B2O5):Ce3+ phosphor is a promising material for near-UV chip-based white LEDs.