Nearest-neighbor Ions Research Articles

An efficient red phosphor LuNb2VO9:Eu3+ with broadband excitation and abnormal thermal quenching properties for personal identification, security ink, and w-LEDs

A series of red-emitting phosphors LuNb2VO9 (LNV):xEu3+ (x = 0.5–45 mol%) were successfully obtained through the high-temperature solid-state reaction. The structure, phase purity, photoluminescence spectra, thermal stability properties, and color purity of the obtained phosphors were systematically examined. The LNV:Eu3+ phosphor exhibits broadband excitation due to the O2-→Eu3+ and O2-→V5+ charge transfer. The LNV:Eu3+ phosphor excited at 316 nm shows four emission peaks at 595, 615, 619, and 699 nm, corresponding to electron transitions from the 5D0 level to the 7F1, 7F2, 7F3 and 7F4 levels. The optimal doped concentration of LNV:xEu3+ is x = 10 mol%. The quenching mechanism is attributed to the nearest neighbor ion interaction. Furthermore, the prepared phosphor exhibits good thermal stability and remarkable activation energy Ea (0.74 eV). In addition, LNV:Eu3+@oleic acid (OA) readily exhibits the level I-III characteristics of fingerprints and the detailed characteristics of lip lines. The successful utilization of LNV:Eu3+ in anti-counterfeiting ink has yielded impressive results. The Commission International de L′ Eclairage (CIE) coordinate of the prepared white light-emitting diode (w-LED) in this study is (0.331, 0.367), accompanied by a color rendering index (Ra) of up to 95. Notably, the results of these experiments indicate that LNV:Eu3+ phosphor possesses exceptional luminescence properties and holds promising applications.

Synthesis, optical properties, and applications of Eu3+, Na+-doped high-color-purity Sr3MgNb2O9 red phosphors for w-LEDs and the detection of latent fingerprints

A series of novel phosphors, doping Eu3+ and Na+ ions in the Sr3MgNb2O9 (SMNO) crystal lattice (SMNO:xEu3+, xNa+, x = 0.5–30 mol%), was successfully synthesized through high-temperature solid-state reaction. X-ray diffraction (XRD) analysis and Rietveld refinement confirmed the successful synthesis of SMNO:Eu3+, Na+. The phosphor belongs to the hexagonal crystal system and the P3¯m1 (No.164) space group. The bandgap energy of SMNO was calculated with Materials Studio and measured with the use of diffuse reflectance spectroscopy. The excitation spectrum of SMNO:Eu3+, Na+ displays multiple narrow absorption peaks in the violet-blue region as well as a charge transfer band (CTB) near 300 nm, exhibiting the highest peak at 394 nm. Four distinct characteristic peaks are observed in the emission spectrum of SMNO:Eu3+, Na+. Notably, the peak at 601 nm shows the highest emission intensity due to the radiative transition from 5D0→7F2. By varying doping concentrations, it was determined that an optimal concentration of 5 mol%Eu3+ resulted in phosphors, with high color purity exceeding 99 %. Concentration quenching is attributed to the nearest neighbor ions interaction. Furthermore, SMNO:Eu3+, Na+ exhibited good stability in 300–480 K, with luminescent intensity remaining 68.6 % at 420 K and 54.4 % at 480 K compared to room temperature (300 K). The internal quantum efficiency (IQE) of SMNO:5%Eu3+, 5 %Na+ is 65.0 %. Both red and white light-emitting diodes (LEDs) were prepared using SMNO:Eu3+, Na+. The chromaticity coordinates of w-LED were measured as (0.357, 0.376), correlating to a correlated color temperature (CCT) of 4685 K and exhibiting a good color rendering index (CRI, Ra = 88). Additionally, the latent fingerprint (LFP) development demonstrated clear visualization of Levels I-III characteristic structures of fingerprints when utilizing SMNO:Eu3+, Na+. These findings suggest promising applications for SMNO:Eu3+, Na+ in w-LED lighting and LFP development.

Magnetocaloric effect in a high-spin ferromagnetic molecular cluster.

The reaction of MnCl2·4H2O with HL ((1-methyl-1H-imidazol-2-yl)methanol) and pdH2 (1, 3 propanediol) in a basic MeCN solution results in the formation of a mixed-valence [Mn20] cationic cluster and two [MnIICl4] counter anions. The metallic skeleton of the cluster describes two geometrically equivalent mixed-valent, linked [MnIII 6MnII 4] supertetrahedra in which nearest-neighbor metal ions have a different oxidation state. Magnetic susceptibility, magnetization data and heat capacity measurements support evidence of predominant ferromagnetic correlations, leading to a s = 22 spin ground state for the [MnIII 6MnII 4] supertetrahedra, which are pair-linked by a weak antiferromagnetic coupling. The properties are discussed in the context of the magnetocaloric effect and the potential application of this compound in cryogenic refrigeration.

Exploring luminescent color tunability and efficient energy transfer mechanism of a single-phased hexagonal nanophosphor for white light emitting diodes (WLEDs) application

Nowadays, NUV-triggered phosphor-converted white light-emitting diodes (pc-WLEDs) have gained prominence as substantial alternatives to conventional incandescent and fluorescent lamps as a source of illumination. In this study, we have successfully developed a Tm3+ codoped La2O3:Sm3+ nanophosphor and investigated its potential suitability for application in white light-emitting diodes (WLEDs). X-ray diffraction (XRD) analysis was conducted to examine the phase impurity and structural characteristics of the synthesized nanophosphor. The analysis confirmed the formation of a single-phase La2O3 nanophosphor with a hexagonal crystal structure. The FT-IR spectrum of the synthesized nanophosphor exhibited distinct peaks associated with the vibrational frequencies of La-O bonds. The peaks observed in the fingerprint region of the spectrum, indicate the presence of La-O atoms in the nanophosphor. However, the HR-TEM analysis confirmed that the prepared nanophosphor had a polycrystalline nature and the observed particle sizes lay within the nanoscale range. The incorporation of Tm3+ ions into the host matrix led to a reduction in the optical band gap, leading to enhanced emission intensity. The photoluminescence (PL) study reveals that the Tm3+ ion exhibited blue emission upon excitation at 360 nm, whereas the Sm3+ ion emits reddish-orange light when excited at 379 nm and 408 nm, respectively. However, under 325 nm excitation, the nanophosphor exhibited a white emission color that resulted from the blending of colors emitted by both Tm3+ and Sm3+ ions. This unique finding suggests that this nanophosphor has the potential to generate white light specifically under this particular excitation wavelength. The efficient energy transfer between Tm3+ and Sm3+ ions was attributed to the electric multipolar interaction between the nearest neighbor ions, leading to a quenching phenomenon. Furthermore, the photometric analysis revealed that the correlated color temperatures (CCTs) associated with the emitted white light were found to be higher than 4000 K. Thus, based on these characteristics, it can be inferred that the prepared nanophosphor has the potential to be utilized as a cool white-emitting nanophosphor for single-phased WLEDs application.

Development of a novel Eu3+-doped tantalate red-emitting phosphor for w-LEDs application

Two novel phosphors LiBa4(1‒x)Eu4xTa3O12 (H-LBTO:xEu3+) and Li0.25Ba1‒xEuxTa0.75O3 (C-LBTO:xEu3+) were prepared successfully by a molten salt method. The transformation between these two structures was realized by changing the sintering temperature or changing the Eu3+ ions concentration, which was also demonstrated by the X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectra (DRS), and photoluminescence excitation (PLE) analyses. Both the sintering temperature and the Eu3+ ions doping concentration have significant impact on the formation of the crystal phase. All these phosphors sintered at 1023 K exhibit two major luminescence lines at 594 and 614 nm under near-UV light of 395 nm excitation, corresponding to Eu3+ ions typical transitions of 5D0→7F1 and 5D0→7F2. The optimum concentration of Eu3+ ions is 9 mol% for C-LBTO:xEu3+ samples and the quenching interaction type is the nearest-neighbor ion interaction. The thermal stability of the C-LBTO:0.09Eu3+ sample was investigated in detail and the device application further suggests that C-LBTO:0.09Eu3+ can be used as a red phosphor for near-UV excited w-LEDs in lighting.

Single- and dual-band emission CaNb2O6:Mn2+: Synthesis and luminescence properties

Now free rare earth ions doped materials have attracted a lot of attention. In this work, CaNb2O6:Mn2+ with a pure phase is synthesized by solid-state method in the reducing atmosphere. The crystal structure and luminescence properties of host (CaNb2O6) and CaNb2O6:Mn2+ are investigated. Host (CaNb2O6) under excitation ultraviolet (UV) light emits blue light. CaNb2O6:Mn2+ can show tunable emission from blue to white. Under excitation 260 nm, blue emission of CaNb2O6:Mn2+ is observed owing to the 4T1(4G) → 6A1(6S) transition of Mn2+. When the excitation wavelength is 314 nm, CaNb2O6:Mn2+ emits white light due to the 4T1(4G) → 6A1(6S) transition of Mn2+ and the 6A1(6S)4T1(4G) → 6A1(6S)6A1(6S) transition in Mn2+ - Mn2+ dimers. We measure the concentration dependent spectra of CaNb2O6:Mn2+ and make sure the optimal Mn2+ doping concentration (∼0.8 mol%). We infer that the concentration quenching mechanism is the electric multipolar interaction between nearest-neighbor ions. Based on the temperature dependent spectra of CaNb2O6:Mn2+, we came to the conclusion that CaNb2O6:Mn2+ has a good thermal stability. We analyze the concentration and thermal quenching mechanisms and explain the luminous mechanism by the Tanabe-Sugano energy level diagram of Mn2+ ion. This research results provide a framework for creating Mn2+-doped luminescent materials.

Using energy transfer to obtain warm white-emitting and thermally stable Ca3Y(AlO)3(BO3)4:Dy3+, Eu3+ phosphors

A series of color-tunable warm white-emitting phosphors Ca3Y(AlO)3(BO3)4:Dy3+,Eu3+ were synthesized and characterized for their crystal structure, luminescence properties, thermal stability, fluorescence decay and energy transfer mechanism. The results show that the optimal excitation wavelength and doping concentration of Ca3Y(AlO)3(BO3)4:Dy3+ phosphor are 350 nm and 0.05 mol%, respectively, and its concentration quenching is mainly caused by the interaction between nearest neighbor ions. Under the excitation at 350 nm, the Ca3Y(AlO)3(BO3)4:Dy3+,Eu3+ phosphor showed prominent emission peaks at 471 nm, 576 nm and 622 nm. The photoluminescence spectrum and lifetime decay curves confirmed the presence of Dy3+→Eu3+ energy transfer in Ca3Y(AlO)3(BO3)4. The phosphor of Ca3Y0·85(AlO)3(BO3)4:0.05Dy3+,0.1Eu3+ exhibited remarkable thermal stability and could maintain 87.68% of the emission intensity at 150 °C. By adjusting the doping ratio of Dy3+ and Eu3+ ions, the CIE coordinates and the related color temperature of Ca3Y(AlO)3(BO3)4:Dy3+,Eu3+ phosphors can be adjusted. The w-LED device packaged with Ca3Y0·85(AlO)3(BO3)4:0.05Dy3+,0.1Eu3+ phosphor can emit warm-white light (Tc = 3284 K, Ra = 72.7). These results suggest that Ca3Y(AlO)3(BO3)4:Dy3+,Eu3+ phosphor can provide a potential alternative for the warm w-LED market.

A novel single phase La2CaZnO5:Dy3+ phosphor for potential applications in WLED's, latent fingerprint and cheiloscopy

Due to the distinctiveness and perseverance of the friction ridges in fingerprints (FPs), latent fingerprints (LFPs) and lip prints (LPs) are two most significant types of evidence at crime scene. Therefore, it is essential in forensic science to develop a reliable method to detect LFPs and LPs. Traditional detection methods still face a number of difficulties, such as limited sensitivity, low contrast, strong background, and complex processing stages. We proposed a method for visualization of LFPs and LPs by utilizing La2CaZnO5:Dy3+ (1–5 mol %) (LCZO: Dy) phosphor using a solution combustion method. The crystal structure, phase purity, particle morphology, photoluminescence (PL) properties of the resulting phosphors were then characterized in detail. SEM images suggested that the obtained phosphors are non-uniform shapes and agglomerated to big particles. The photophysical properties of Dy3+ doped phosphors are analyzed by exploiting their photoluminescence excitation (PLE) and emission profiles. The emission profiles of all the doped samples exhibit sharp emission lines centred at ∼481, 573, and 667 nm, which are ascribed to 4F9/2 → 6H15/2, 4F9/2 → 6H13/2, and 4F9/2 → 6H11/2 intra configurational transitions of Dy3+ ion, correspondingly. The optimum doping concentration of LCZO: Dy phosphor was 4 mol%, and the dominant factor of concentration quenching effect is the nearest-neighbor ions interaction. The chromaticity coordinates of International Committee LCZO: Dy were located in the yellow color area. In addition, LCZO: 4Dy phosphor can well visualize the LFP image and LP image. The levels 1–3 features of fingerprint and groove pattern of lip print can be easily recognised with high resolution and contrast. The experimental results showed La2CaZnO5:Dy3+ can be well applied to advanced forensic investigation.

Synthesis and photoluminescence properties of NaYGeO4:Bi3+ phosphors

In this paper, NaYGeO4:[Formula: see text]Bi[Formula: see text] phosphors were successfully prepared by high-temperature solid-state reaction. XRD patterns and refinement results show that Bi[Formula: see text] ions are successfully incorporated into the matrix material and replaced by Y[Formula: see text]. The emission spectrum shows that the optimal doping concentration of the sample is 0.25%, and it is theoretically studied that the concentration quenching is caused by the nearest neighbor ions. The fluorescence lifetime curve showed that with the increase of Bi[Formula: see text] concentration, the fluorescence lifetime first increased and then decreased. The thermal stability of the sample was studied, and it was found that when the temperature increased to 523 K, the luminescence intensity of the phosphor was still 70% of the initial intensity, and the activation energy was calculated to be 0.306 eV. Finally, the CIE color coordinates of the sample with the best luminous intensity were calculated as (0.1595, 0.0342), and the color coordinates are located in the blue light region.

Synthesis and characterization of a new double perovskite phosphor: NaCaTiTaO6:Dy3+ with high thermal stability for w-LEDs application

A new yellow-emitting phosphor, NaCaTiTaO6:Dy3+, was synthesized via solid-phase synthesis at 1300 ℃. X-ray diffraction (XRD) analysis and Rietveld refinement showed that the prepared phosphors exhibited a stable double perovskite structure. The particle size of the phosphor was around 3.8 μm. The maximum emission peak at 574 nm is attributed to the 4F9/2→6H13/2 energy level transition under irradiation at 389 nm. The optimum Dy3+ doping concentration is 0.10 M equivalent, and concentration quenching is due to the nearest neighbor ion interaction. The luminescence intensity of the phosphor was reduced by only 15% at 420 K, exhibiting high thermal stability. Quantum yield (QY) was measured to be 26.31%. Finally, the Commission International de I’Eclairage (CIE) color coordinate of the phosphor for white light emitting diode (w-LED) was (0.314, 0.323), with a color rendering index (Ra) of 92 and a correlated color temperature (CCT) of 5578 K. Above all, the Dy3+-doped double perovskite NaCaTiTaO6:Dy3+ phosphor is expected to be used in w-LEDs.

Defects in hafnium-doped lutetium oxide and the corresponding electron traps: a meta-generalized gradient approximation study.

A number of Lu2O3-based materials were reported to present efficient capability of trapping excited charge carriers in metastable excited states formed either by specific dopants or naturally occurring defects. Over the years, abundant experimental data have been collected, which were taken as a solid ground to treat the problem using computational chemistry. Density functional theory (DFT) calculations with an advanced meta generalized gradient approximation (mGGA) functional were used to analyze electron trapping in cubic Lu2O3 doped with Hf. Individual ions of dopant and nearest-neighbor dopant ion pairs were considered. The effects of interstitial anions such as O2- and Cl- were analyzed. In most of the analyzed cases the additional electron charge is localized at the dopant site. However, in many of the studied cases, the dopant/defect states overlap with the conduction band and cannot correspond to electron trapping. The Hf3+ ion in the Lu site of C3i local symmetry ({\rm Hf}^{\times}_{{\rm Lu}-C_{\rm 3i}}) corresponds to a moderate trap depth of 0.8-0.9 eV. Several composite defects corresponding to deeper (1.1-1.4 eV) traps also exist. Unambiguous deep traps (1.5-1.8 eV) correspond to systems with Hf dopant in the cationic void, accompanied by two interstitial oxygen atoms. The results thus indicate that basic `Hf-substitutes-Lu' doping is unlikely to correspond to the deep traps observed experimentally in Lu2O3:Tb,Hf andLu2O3:Pr,Hf and more complex defects must be involved.

Muon sites in PbF2 and YF3 : Decohering environments and the role of anion Frenkel defects

Muons implanted into ionic fluorides often lead to a so-called F--$\ensuremath{\mu}$--F state, in which the time evolution of the muon spin contains information about the geometry and nature of the muon site. Nuclei more distant from the muon than the two nearest-neighbor fluorine ions result in decoherence of the F--$\ensuremath{\mu}$--F system, and this can yield additional quantitative information about the state of the muon. We demonstrate how this idea can be applied to the determination of muon sites within the ionic fluorides $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{PbF}}_{2}$ and ${\mathrm{YF}}_{3}$, which contain fluoride ions in different crystallographic environments. Our results can be used to distinguish between different crystal phases and provide strong evidence for the existence of anion Frenkel defects in $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{PbF}}_{2}$.

Synthesis and characterization of wide band excited yellow phosphor LaNb2VO9:Dy3+ and application in potential fingerprint and lip print detection

LaNb2VO9:Dy3+ yellow phosphors were synthesized by high-temperature solid-state method. The luminescent properties, structure, and color purity of the products were studied systematically. LaNb2VO9:Dy3+ phosphors can be effectively excited by two broad charge transfer bands (CTB) under 307 nm excitation. The strong yellow light at 570 nm was caused by the 4F9/2 → 6H13/2 energy level transition of Dy3+. The optimum doping concentration of LaNb2VO9:xDy3+ phosphor was x = 0.10 mol, and the dominant factor of concentration quenching effect is the nearest-neighbor ions interaction. The chromaticity coordinates of International Committee LaNb2VO9:Dy3+ were located in the yellow color area. In addition, LaNb2VO9:0.1Dy3+ phosphor can well visualize the latent fingerprint (LFP) image and lip print image. The levels 1–3 features of fingerprint and groove pattern of lip print can be easily recognized, with high resolution and contrast. The experimental results showed LaNb2VO9:Dy3+ can be well applied to LFP and lip print detection.

Self-Activated and Bismuth-Related Photoluminescence in Rare-Earth Vanadate, Niobate, and Tantalate Series-A First-Principles Study.

Rare-earth vanadates, niobates, and tantalates have shown self-activated and Bi3+-activated emissions. Their intrinsic emission has been attributed to self-trapped excitons (STEs), but the detailed information concerning the geometric and electronic structures of the excited states has remained unknown. Regarding the Bi3+ dopants in these hosts, the luminescence has been attributed to two different mechanisms, i.e., Bi3+↔ (V/Nb/Ta)5+ metal-to-metal charge transfer and interconfigurational (3P0,1 → 1S0) transition. Here, first-principles calculations using hybrid functionals are employed to resolve these issues. The STEs are shown to be composed of an electron localized on an individual vanadium, niobium, or tantalum ion and a hole localized on a single nearest-neighbor oxygen ion that is not shared by covalent complexes, and the bond length of the (V/Nb/Ta)-O bond with oxygen accommodating the hole is significantly elongated. The Bi3+-related emission is identified as the recombination of an exciton with a hole and an electron localized correspondingly at Bi3+ and (V/Nb/Ta)5+ ions, while the excitation is dominated by the 6s → 6p transition of Bi3+. Furthermore, Bi3+ has a hole trap level in all of the hosts considered with the trap levels in the vacuum-referred binding energy diagram being nearly flat but has an electron trap level only in rare-earth tantalates. Furthermore, the long-wavelength emission observed in niobates and tantalates is interpreted based on our calculations to be excitons bound to intrinsic defects. The insights gained in this work deepen our understanding of the STEs and form the basis for interpreting similar luminescence phenomena in other ternary closed-shell d0 transition-metal oxides. The clarification of Bi3+-related transitions and the analyses with the vacuum-referred binding energy diagram may find applications for the design and optimization of Bi3+-activated phosphors.

Effect of Sm3+ concentration and excitation wavelength on spectroscopic properties of GdPO4:Sm3+ phosphor

Gd(1−x)SmxPO4 ((1, 2, 3 and 5 mol%) nanophosphors have been synthesized via combustion route. The phase structure and the morphology of the obtained compounds have been identified by X-ray powder diffraction analysis, FTIR spectroscopy and scanning electron microscopy (SEM). The luminescence properties of the phosphor have been investigated based on photoluminescence excitation and emission spectra, and decay curves. The photoluminescence excitation spectra of the phosphors show large number of excitation bands related to the charge transfer state and 4–4 f electronic transitions of Sm3+ and Gd3+ ions. The photoluminescence spectra registered under excitation in CTB, 6IJ level of Gd3+ and the 4F7/2 level of Sm3+ show different profiles and emission intensity trends as a function of Sm3+ concentrations. The decay time curves have double exponential profiles and the registered lifetimes depend on the excitation wavelength and the Sm3+ concentration. The possible cross relaxation channels have been discussed based on the near infrared emission of Sm3+ under excitation with 273 nm and 401 nm. The evaluation of emission intensities and decay times curves analysis converge to a dipole-dipole interaction under excitation with 273 nm, while under excitation with 401 nm, a nearest-neighbor ions energies transfer mechanism between Sm3+-Sm3+ ions is dominant. Cool white and pure orange emissions have been obtained upon excitation with 229 and 401 nm, respectively, which may be suitable candidates for displays and photonic devices.

Photoluminescence properties and energy transfer studies of Ba2YAlO5: Sm3+, Eu3+ orange-red phosphors

Specify types phosphors in single dope xSm3+(x = 0, 0.2, 0.4, 0.6, 0.8, 0.12) and co-dope 0.04Sm3+/yEu3+(y = 0.02, 0.04, 0.08, 0.16) of Ba2YAlO5 (BYAO) were employed by conventional solid-state method. The structure, micro-morphology and luminescence properties of these samples were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). Under 404 nm excitation, the BYAO: Sm3+ exhibit three sharp lines at 567, 604 and 653 nm result from 4G5/2→6HJ (J = 5/2, 7/2, 9/2) prohibition transition of Sm3+. Meanwhile, specify types BYAO phosphors co-dope 0.04Sm3+/yEu3+ exhibit orange-red sharp broadband emission. Phosphors of BYAO: 0.04Sm3+/yEu3+ fluorescence lifetime is negatively correlated with Eu3+ doping concentration. Energy transfer mechanism (ETM) between Sm3+ and Eu3+ belong to the nearest neighbor ions interaction. The BYAO: 0.04Sm3+, 0.08Eu3+ phosphors measure temperature ranging from 298 to 573 K, which shows that the phosphors have good thermal stability. The co-doped 0.04Sm3+, 008Eu3+ of BYAO phosphors has better color purity than single-doped Sm3+. The above results have indicated this phosphor as the red-light component has potential applications in white light emitting diodes (WLEDs).

Effect of charge compensators (Li+, Na+, K+) on the luminescence properties of Sr3TeO6:Eu3+ red phosphor

A double-perovskite Sr3TeO6:Eu3+ red phosphor was successfully prepared and confirmed to be a single phase through X-ray diffraction. Under an optimal excitation wavelength (394 nm), the Sr3TeO6:Eu3+ phosphor emitted intense red light at 617 nm, which corresponded to 5D0→7F2 transition. When the concentration of Eu3+ exceeded the optimal doping concentration (25 mol%), concentration quenching occurred because of the interactions among the nearest neighbor ions. The phosphor exhibited excellent thermal stability, and the Ea value was 0.27 eV. In accordance with Judd–Ofelt theory, the low symmetry of Eu3+ ions was confirmed, and it resulted in a color purity of up to 99.5%–99.8%. Among the charge compensators (Li+, Na+, and K+), the Na+ ions had the best charge compensation effect. The luminescence intensity of Sr3TeO6:Eu3+, Na+ was approximately 2.06 times that of Sr3TeO6:Eu3+ and 2.25 times that of commercial phosphor (Y2O3:Eu3+). The fabricated red LED has the potential to be used for plant and herb cultivation. A white light–emitting diode (w–LED) was successfully prepared, and related parameters were established. The Ra value of the prepared w–LED was as high as 91, and R9 was 5.7 times that of a commercial w–LED. These characteristics indicate that phosphors have potential in the solid-state lighting field.

New red-emitting Li3Bi3Te2O6:Eu3+ phosphors with high color purity for white light-emitting diodes

This work is the first to synthesize the red-emitting Li3Bi3Te2O6 phosphors using the conventional high-temperature solid-state reaction. The phase purity, particle morphology, and luminescent properties are analyzed in detail. Upon the near-ultraviolet (n-UV) excitation on 395 nm, Li3Bi3Te2O6:Eu3+ phosphors show four emission peaks due to 5D0 → 7FJ (J = 1, 2, 3, 4) transitions and the strongest peak is at 610 nm (5D0 → 7F2). The best doping concentration of Eu3+ ions is found to be 0.45 mol. The critical transfer distance (Rc) of the energy transfer between the Eu3+ ions reaches 11 A and the luminescence quenching is confirmed by the nearest-neighbor ions interaction. The commission international de l'Eclairage (CIE) chromaticity coordinates (0.655, 0.344) of Li3Bi3Te2O6:0.40Eu3+ phosphors are in the red region. The values of decay time are calculated in the millisecond time range from 0.878 to 0.493 ms. Phosphors show common thermal stability with activation energy (0.25 eV). All the properties indicate that Li3Bi3Te2O6:Eu3+ phosphors have potential applications in displays and photonic devices.

Coulomb expansion of a cold non-neutral rubidium plasma

We study the expansion of a strongly coupled, non-neutral, and cylindrically arranged ion plasma into the vacuum. The plasma is made from cold rubidium atoms in a magneto-optical trap (MOT) and is formed via ultraviolet photoionization. Higher-density and lower-density plasmas are studied to exhibit different aspects indicative of strong coupling. In a higher-density regime, we report on the formation and persistence of plasma shock fronts, as well as external-field-induced plasma focusing effects. In the lower-density regime, conditions are ideal to observe the development and evolution of nearest-neighbor ion correlations, as well as geometry-induced asymmetries in the pair correlation function. Simulated results from a trajectory model and a fluid model are in good agreement with the measurements.

Why Do Relative Intensities of Charge Transfer and Intra-4f Transitions of Eu3+ Ion Invert in Yttrium Germanate Hosts? Unravelling the Underlying Intricacies from Experimental and Theoretical Investigations.

The dominant intensity of parity-forbidden intra-4f transitions of europium(III) over O → Eu charge-transfer band (CTB) intensity is against common perceptions, yet this trend is observed in many germanate hosts and has not been rationalized so far. In search of a plausible explanation for this unusual trend, present work reports an experimental and theoretical investigations in conjunction on two sibling germanate host, namely, Y2GeO5 and Y2Ge2O7 having dopant Eu3+ in their respective YO7 polyhedra. Whereas for Y2GeO5:Eu3+, the CTB is more intense than the intra-4f transitions in the excitation spectrum, in the case of Y2Ge2O7:Eu3+, the relative intensities of CTB and intra-4f transitions are reversed. Comparative structural analysis reveals that Eu3+ present in YO7 of Y2GeO5 has a greater number of tetra-coordinated oxygen (Otetra) and yttrium atom as first and second neighbors, respectively (Eu3+-Otetra-Y3+ linkages). Conversely, in Y2Ge2O7 host, the Eu3+ ion mostly has tricoordinated oxygen (Otri) as its nearest neighbor and germanium ions next to Otri (Eu3+-Otri-Ge4+ linkage). Theoretical calculations reveal that while Y2GeO5:Eu has Otetra(4Y) dominating at the Fermi level and the 4f state of Eu3+ remains inert toward mixing, in Y2Ge2O7:Eu, the Fermi level has major contribution from Otri(2Y + 1Ge) with significant mixing with 4f states of Eu. The dominant control of Eu3+-Otri-Ge4+ linkages in geometrical and electronic structure of Y2Ge2O7:Eu owing to the GeO4 surrounding has been attributed to relative poor intensity of O → Eu CTB. Siege of Eu3+ by GeO4 and subsequent occurrence of Eu3+-Otri-Ge4+ linkages play a dual role: First, it induces electronic rigidity to hinder excitation of electron at bridging (Otri) oxygen by highly charged small Ge4+ cation; second, the covalent character in Eu-O bond is achieved by intermixing of Eu's 4f and Otri 2p orbital which facilitates relaxing of the parity-selection rule thus enhancing the probability of intra-4f transitions. The inferences drawn remain valid when extrapolated to other inorganic oxides having EuOx polyhedra surrounded by covalent units like PO4, SiO4, etc. and have a prevailing number of low-coordinated oxygen atoms and highly charged small cation in the first and second coordination shells, respectively. The optical basicity concept is also found to endorse our explanation. These remarkable generic inferences will pave the rational way for designing efficient phosphors for solid-state lighting.