Eu3+-doped Bi4Si3O12 red phosphor for solid state lighting: microwave synthesis, characterization, photoluminescence properties and thermal quenching mechanisms

Realizing Ultrabroadband NIR-II Emission and Wide-Range Wavelength Tuning in Cr4+-activated ABO2 (A = Li, Na; B = Al, Ga) Phosphors

Cr4+-activated phosphors are important candidate materials for NIR-II light sources, but providing a suitable lattice coordination environment for Cr4+ and achieving long wavelength broadband emission remains a challenge. In this work, a series of Cr4+-activated ABO2 (A = Li, Na; B = Al, Ga) phosphors were successfully prepared. Due to the presence of only tetrahedral coordination structures available for Cr4+ to occupy in the matrix crystal ABO2, the valence state and luminescence stability of Cr4+ are effectively guaranteed. Through the cation substitution design of A-site (Na → Li) and B-site (Ga → Al), the [BO4] tetrahedron is distorted and expanded, which degrades the symmetry of the Cr4+ coordination crystal field. Consequently, the central wavelength of the Cr4+ emission peak is tuned from 1280 to 1430 nm, and the fwhm is significantly extended from 257 to 355 nm. Thebroadband NIR-II light sources constructed with LiAlO2: 0.03Cr4+ and NaGaO2: 0.03Cr4+ phosphors verify their important potential applications in nondestructive testing and biological imaging.

Cation vacancy-boosted BaZnB4O8:xEu3+ phosphors with high quantum yield and thermal stability for pc-WLEDs

Achieving high luminescent quantum yield and thermal stability of phosphors simultaneously remains challenging, yet it is critical for facilitating high-power white light emitting diodes (WLEDs). Herein, we report the design and preparation of the layered structure BaZnB4O8:xEu3+ (0.10 ≤ x ≤ 0.60) red phosphors with high quantum yield (QY = 76.5%) and thermal stability (82.8%@150 °C) by the traditional solid-state reaction method. The results of XRD and Rietveld refinement show that the presence of Eu3+ ions at Ba2+ sites causes the formation of cation (Zn2+/Ba2+) vacancies in the lattice. The PL and PL decay results reveal that the quenching concentration of BZBO:xEu3+ phosphors is as high as 50%, and the lifetime remains unchanged with Eu3+ concentration due to the unique structure of the host and the cation vacancies generated by the heterovalent substitution. Furthermore, on a 395 nm near-UV chip, a pc-WLED device with exceptional optical performance (CCT = 4415 K, CRI = 92.1) was realized using the prepared BZBO:0.50Eu3+ as a red phosphor. Simple synthesis and excellent performance parameters suggest that the reported BaZnB4O8:xEu3+ phosphors have promising applications in high-power pc-WLEDs. At the same time, it also indicates that cationic vacancy engineering based on heterovalent ion substitution is a potential strategy for improving luminescence quantum yield and thermal quenching performance.

Multicolor tunable bright photoluminescence in Ca2+/Mg2+ modified Eu3+ doped ZnGa2O4 phosphors under UV excitation for solid state lighting applications

The Eu³⁺ doped and Mg²⁺/Ca²⁺ co-doped ZnGa₂O₄ phosphor samples were synthesized by solid-state reaction method and their structural and optical properties studied. The phase, crystallinity and particles size of the phosphor samples were studied by XRD and SEM measurements. EDS analyses were used to identify the elements present in the phosphor materials. The vibrational groups present in the phosphor samples were examined by Fourier transform infrared (FTIR) measurements. Pure ZnGa₂O₄ emits intense blue light under 260 nm excitation. However, Eu³⁺ doped and Mg²⁺/Ca²⁺ co-doped ZnGa₂O₄ phosphor samples exhibit intense red emission under 393 nm excitation. A bluish white color is observed in these samples under 290 nm excitation. The maximum PL emission intensity is found at 0.1 mol% Eu³⁺ doping concentration. For higher concentrations, concentration quenching was observed due to dipole-dipole interaction. The emission intensity is enhanced upto 1.20 and 2.91 times on co-doping of Mg²⁺ and Ca²⁺via induced crystal field due to charge imbalance. The emission intensity of the phosphor is found to enhance further on annealing the samples at 873 K. Under various excitation wavelengths, color tunability was seen from blue to bluish-white to red regions. The lifetime of the ⁵D₀ level of the Eu³⁺ ion improves via doping of Mg²⁺/Ca²⁺ ions and it increases appreciably on annealing. The temperature dependent photoluminescence study (TDPL) reveals a thermal quenching behavior of the sample with thermal stability ∼65% and activation energy ∼0.223 eV in the Eu³⁺/Ca²⁺ co-doped ZnGa₂O₄ phosphor sample.

Excitation-Dependent Photoluminescence of BaZrO3:Eu3+ Crystals

The elucidation of local structure, excitation-dependent spectroscopy, and defect engineering in lanthanide ion-doped phosphors was a focal point of research. In this work, we have studied Eu³⁺-doped BaZrO₃ (BZOE) submicron crystals that were synthesized by a molten salt method. The BZOE crystals show orange-red emission tunability under the host and dopant excitations at 279 nm and 395 nm, respectively, and the difference is determined in terms of the asymmetry ratio, Stark splitting, and intensity of the uncommon ⁵D₀ → ⁷F₀ transition. These distinct spectral features remain unaltered under different excitations for the BZOE crystals with Eu³⁺ concentrations of 0-10.0%. The 2.0% Eu³⁺-doped BZOE crystals display the best optical performance in terms of excitation/emission intensity, lifetime, and quantum yield. The X-ray absorption near the edge structure spectral data suggest europium, barium, and zirconium ions to be stabilized in +3, +2, and +4 oxidation states, respectively. The extended X-ray absorption fine structure spectral analysis confirms that, below 2.0% doping, the Eu³⁺ ions occupy the six-coordinated Zr⁴⁺ sites. This work gives complete information about the BZOE phosphor in terms of the dopant oxidation state, the local structure, the excitation-dependent photoluminescence (PL), the concentration-dependent PL, and the origin of PL. Such a complete photophysical analysis opens up a new pathway in perovskite research in the area of phosphors and scintillators with tunable properties.

Structural and Optical properties of a new Milarite type Na3 Mg4 LiSi12 O30 :Eu3+ phosphor

A new red-emitting Eu³⁺ (1-17mol%) doped Na₃ Mg₄ LiSi₁₂ O₃₀ (NMLS) phosphor was prepared by conventional solid state reaction method at low temperature. The prepared samples belong to a hexagonal structure with well-matched JCPDS card No.73-0934. The photoluminescence (PL) emission spectrum showed an intense peak at 612nm when excited at 393nm. The variation of electric dipole transition (⁵ D₀ -⁷ F₂ ) emission intensity with increasing Eu³⁺ ion concentration was investigated. The concentration quenching at 11mol% is due to dipole-dipole interaction mechanism in the NMLShost. The optimized NMLS:Eu³⁺ phosphor shows 2.18 times higher luminescence intensity than the (Y,Gd)BO₃ (YGB) commercial phosphor. The NMLS:Eu³⁺ showed an intense red emission having CIE coordinates (0.6280, 0.3691) and color purity of 99.2%. The resulting phosphor exhibits good thermal stability of 80% at 423K. The magnified images of fingerprint showed various minute features such as bridges, sweat pores, ridge end, bifurcation, island and core with better visualization under 393 nm excitation. Furthermore, the optimized NMLS:Eu³⁺ was employed for pc-LED, latent fingerprints and anti-counterfeit applications as a promising red phosphor.

Sensitization of lanthanide complexes through direct spin-forbidden singlet → triplet excitation

Ln^III complexes may display luminescence within the ultraviolet-visible-near-infrared spectral window and although they render bright emissions mainly due to the classical singlet-triplet-state-assisted ligand sensitization, which would be the photophysical parameters if they could be excited through direct spin-forbidden singlet → triplet transitions? Herein, we report the sensitization of Ln complexes through spin-forbidden S₀ → T transitions in a series of homobimetallic Eu^III, Tb^III, Er^III, and Yb^III complexes with halogen-substituted benzoate ligands. As halogens and Ln^III atomic numbers increase, intense singlet → triplet absorption/excitation bands and relative quantum yields up to 18% were achieved due to an increased spin-orbit coupling effect. Moreover, the near-UV-shifted excitation may enable application in luminescent solar concentrators where Yb^III near-infrared luminescence matches the maximum efficiency of the crystalline Si photovoltaic cell. Therefore, the spin-relaxed excitation channel provides new opportunities to improve the Ln^III complex luminescence and potential within the energy conversion field.

Tunable photoluminescence and energy transfer of Eu3+,Ho3+-doped Ca0.05Y1.93-xO2 nanophosphors for warm white LEDs applications

A series of Eu3+ ions doped Ca0.05Y1.93-xO3:0.02Ho3+ (CYO:Ho3+,xEu3+) nanophosphors having multicolour tuneability have been synthesised by following a simplistic solution combustion approach. The synthesised samples have been characterised by employing X-ray diffraction (XRD), Transmission electron microscope (TEM), and Fourier transforms infrared spectroscopy (FTIR). The optical properties have been engrossed by UV-visible and photoluminescent excitation and emission spectra, and decay lifetimes measurements. The characteristic emission, which occurs due to the f-f transition of Ho3+ and Eu3+ has been observed in emission spectra with excitation of 448 nm. By adjusting the doping ratio of Ho3+/Eu3+, the as-synthesized nanophosphor accomplishes multicolour tunability from green-yellow to red. Emission spectra and decay lifetime curve recommend dipole-dipole interaction causes energy transfer from Ho3+ → Eu3+. The energy transfer process from Ho3+ to Eu3+ has been confirmed through electric dipole-dipole interaction with critical distance 15.146 Å. Moreover, temperature dependent emission spectra show the high thermal stability with an activation energy ⁓ 0.21 eV, with the quantum efficiency of 83.6%. CIE coordinate illustrates that the singly doped Ho3+ and Eu3+ lie in the green and red region, respectively, while the as-synthesized CYO:Ho3+,xEu3+shows tunability from green to red with low CCT and high colour purity values. Hence, the CYO:Ho3+,xEu3+nanophosphor may be a near-UV excited multicolour colour-tunable pertinent candidate with potential prospects for multicolour- display and near-ultraviolet lighting applications.

Crystallographic control for Cr4+ activators toward efficient NIR-II luminescence

Broadband near-infrared (NIR) emitting phosphors have attracted many studies due to their potential applications in non-destructive examination and bioimaging. However, most of the reported broadband NIR phosphors emit in NIR-I...

Revealing Eu3+-doped yttrium pyrogermanate as a soft UV excitable phosphor: retaining the pros of the commercial phosphor and compensating for the cons

This article presents the synthesis of a single-phase red emitting Y2Ge2O7:Eu3+ soft-UV excitable phosphor with up to 10% Eu3+ content. Experimental and theoretical exploration has established its relative potential with respect to the commercial Y2O3:Eu3+ phosphor.

Efficient and ultra-thermally stable Eu3+ and Sm3+-activated narrow-band red/deep red-emitting phosphors and their versatile applications

A succession of Eu³⁺-activated Na₂Y₄(WO₄)₇ (NYW) red phosphors were synthesised and their optical properties were studied in detail for white LED, latent fingerprint and plant growth applications. The phosphors crystallised in a tetragonal system with space group I4₁/a. The NYW:Eu³⁺ red phosphors demonstrated a line-like emission at 616 nm owing to electric dipole transition, and a systematic concentration-dependent PL study revealed that concentration quenching occurs at x = 1.8 with a color purity of 96.06%. The thermal stability and internal quantum efficiency of the phosphor were found to be ∼75.54% (at 423 K) and 88%, respectively. Furthermore, solid solution phosphors were synthesized to increase QE, which was found to be 91.27%. Specifically, the hybrid white LED exhibits warm white light with high CRI (80) and low CCT (5730 K) values, and these values are further improved (CRI-81, CCT-4274 K) when the WLED is fabricated using the most efficient solid solution phosphor Na₂Y_2.2Eu_1.8(WO₄)₃(MoO₄)₄. The currently synthesized phosphors can be potential candidates for security applications. The selected phosphor compositions can be used for the detection of latent fingerprints. Besides, a succession of Eu³⁺ and Sm³⁺ co-doped phosphors were synthesized and their photophysical properties were studied systematically. The deep red LED was fabricated using the same and this could be a possible light source for plant growth usage.

Microwave-Assisted Preparation of Luminescent Inorganic Materials: A Fast Route to Light Conversion and Storage Phosphors

Luminescent inorganic materials are used in several technological applications such as light-emitting displays, white LEDs for illumination, bioimaging, and photodynamic therapy. Usually, inorganic phosphors (e.g., complex oxides, silicates) need high temperatures and, in some cases, specific atmospheres to be formed or to obtain a homogeneous composition. Low ionic diffusion and high melting points of the precursors lead to long processing times in these solid-state syntheses with a cost in energy consumption when conventional heating methods are applied. Microwave-assisted synthesis relies on selective, volumetric heating attributed to the electromagnetic radiation interaction with the matter. The microwave heating allows for rapid heating rates and small temperature gradients yielding homogeneous, well-formed materials swiftly. Luminescent inorganic materials can benefit significantly from the microwave-assisted synthesis for high homogeneity, diverse morphology, and rapid screening of different compositions. The rapid screening allows for fast material investigation, whereas the benefits of enhanced homogeneity include improvement in the optical properties such as quantum yields and storage capacity.

Efficient and stable Sr3Eu2B4O12 red phosphor benefiting from low symmetry and distorted local environment

The development of suitable red phosphors to obtain improved white color stands a good chance to serve in the new generation of white light-emitting diodes. Owing to multi-elements via doping and oxidation of reduced valence state of lanthanide or transition metal ions, most of the reported phosphors usually suffer from complex synthetic processes and unstable color of the lighting industry cycle. In this work, we present a new red emitting and stable Sr₃Eu₂B₄O₁₂ phosphor with regard to its special structure. It crystallizes as an orthorhombic cell, with Sr and Eu atoms co-occupying three different lattice sites in the space group of Pnma (no. 62). It is proposed that the long bond distance between activators minimizes the content quenching, while the high disorder of location restricts the thermal quenching. This phosphor emits bright red light with good color purity under UV excitation, with the luminescence intensity and quantum yield tunable via the fabrication temperature. Through a preliminary optimization of the synthesis process, the Sr₃Eu₂B₄O₁₂ phosphor prepared at 1250 °C has high quantum yields of about 94.7% and excellent thermal stability of 85.6% intensity retention at 150 °C relative to the initial value at room temperature. The calculated Judd-Ofelt intensity parameters (Ω₂, Ω₄) further clarified that the Eu³⁺ site in Sr₃Eu₂B₄O₁₂ had lower symmetry without an inversion center, and more distorted local environment and structural rigidity of the host, predicting excellent thermal stability. Finally, a warm pc-WLED device has been produced by mixing as-prepared Sr₃Eu₂B₄O₁₂ powders and commercial BaMgAl₁₀O₁₇:Eu²⁺ and (Sr, Ba)₂SiO₄:Eu²⁺ phosphors, which exhibits a high color rendering index (R_a = 83.4) along with a color temperature at around 4102 K. The present work indicates that the Sr₃Eu₂B₄O₁₂ phosphor is an efficient red component with excellent thermal stability for white-light production of near-UV-excited w-LEDs.

Synthesis and Research of Rare Earth Nanocrystal Luminescent Properties for Security Labels Using the Electrohydrodynamic Printing Technique

YVO4:Eu3+ nanoparticles were successfully synthesized by two methods, namely the sonochemical method and hydrothermal method. The X-ray diffraction (XRD) patterns showed the tetragonal phase of YVO4 (JCPDS 17-0341) was indexed in the diffraction peaks of all samples. The samples synthesized by the sonochemical method had a highly crystalline structure (X-ray diffraction results) and luminescence intensity (photoluminescence results) than those synthesized by the hydrothermal method. According to the results of field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), the average size of YVO4:Eu3+ nanoparticles was around 25–30 nm for the sonochemical method and 15–20 nm for the hydrothermal method. YVO4:Eu3+ nanoparticles in the case of the sonochemical method had a better crystalline structure and stronger emissivity at 618 nm. The Eu3+ ions’ average lifetime in YVO4:Eu3+ at 618 nm emission under 275 nm excitation were at 0.955 ms for the sonochemical method and 0.723 ms for the hydrothermal method. The security ink for inkjet devices contained YVO4:Eu3+ nanoparticles, the binding agent as polyethylene oxide or ethyl cellulose and other necessary solvents. The device used for security label printing was an inkjet printer with an electrohydrodynamic printing technique (EHD). In the 3D optical profilometer results, the width of the printed line was ~97–167 µm and the thickness at ~9.1–9.6 µm. The printed security label obtained a well-marked shape, with a size at 1.98 × 1.98 mm.

Yolk–shell structured Bi2SiO5:Yb3+,Ln3+ (Ln = Er, Ho, Tm) upconversion nanophosphors for optical thermometry and solid-state lighting

Bi₂SiO₅:Yb³⁺,Er³⁺ yolk–shell nanophosphors have been successfully synthesized, which are expected to find important applications in optical thermometry and solid-state lighting.

High performance red/deep-red emitting phosphors for white LEDs

NaSrGd(MoO₄)₃:Eu³⁺ red phosphor exhibits higher quantum efficiency (82%) and the fabricated white LED showed 74% CRI and 6823 K CCT.

Highly efficient near-infrared phosphor LaMgGa11O19:Cr3+

LaMgGa₁₁O₁₉:Cr³⁺ phosphor was synthesized successfully, showing broadband NIR emission centered at ∼770 nm, high efficiency and excellent thermal quenching resistance for pc-LEDs.

Facile synthesis, structure, and tunable luminescence properties of novel one-dimensional Bi4Si3O12 fibers

A series of novel one-dimensional Bi₄Si₃O₁₂ fibers with tunable luminescence have been synthesized via the electrospinning method for the first time.

Scandium Molybdate Microstructures with Tunable Phase and Morphology: Microwave Synthesis, Theoretical Calculations, and Photoluminescence Properties

In this paper, scandium molybdate microstructures have been prepared from solution via a microwave heating method. By controlling the experimental parameters such as molar ratio of reagent and reaction time, scandium molybdates with tunable phase and diverse morphologies including snowflakes, microflowers, microsheets, and branched spindles were obtained. The density of states and surface energies of Sc₂Mo₃O₁₂ were primarily studied from first-principles calculations. An indirect band gap of 3.56 eV was observed for crystalline Sc₂Mo₃O₁₂, and the surface energies of various facets were determined to be 0.27-0.91 J/m². The influence of n(Sc³⁺): n(Mo₇O₂₄^6-) (short for Sc/Mo) molar ratio was systematically investigated and well-characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and UV-vis absorption spectroscopy (UV-vis). Results indicate that the Sc/Mo molar ratio has a great effect on the phase and morphology. Diffuse reflection spectra (DRS) revealed the E_gap can be readily tuned from 3.69 to 4.16 eV, which is in accordance with the theoretical result. The photoluminescence (PL) properties of Eu³⁺-doped Sc₂Mo₃O₁₂ were discussed. This facile synthesis strategy could be extended to the synthesis of other molybdates.

Double perovskite Cs2AgInCl6:Cr3+: broadband and near-infrared luminescent materials

A Cr³⁺-doped halide double perovskite Cs₂AgInCl₆:Cr³⁺ is first reported which exhibits a broad near-infrared emission ranging from 850 to 1350 nm centered at 1010 nm with a FWHM of 180 nm.

Correlating Structure and Luminescence Properties of Undoped and Eu3+-Doped La2Hf2O7 Nanoparticles Prepared with Different Coprecipitating pH Values through Experimental and Theoretical Studies

Understanding the structure-property relationship and optimizing properties of phosphors for use in lighting and scintillation fields is an important materials challenge. In this work, we investigated the effects of the pH value of the coprecipitating solution adjusted by the concentration of NH₄OH(aq) on the structure and optical properties of the obtained La₂Hf₂O₇ nanoparticles (NPs). The obtained NPs stabilize in the ideal pyrochlore structure, but the extent of ordering increased with an increase in the pH value used. The NPs prepared at pH = 12.1 displayed the best optical performance owing to the balance of the crystallinity, agglomeration, and surface defects. On the basis of density functional theory (DFT) calculations, the origin of violet-blue emission in undoped La₂Hf₂O₇ NPs was attributed to defect states in the electronic band gap arising due to oxygen defects. For the La₂Hf₂O₇:Eu³⁺ NPs, the Eu³⁺ dopants possess low symmetry and their occupancy is more favorable at the LaO₈ site. DFT calculations further justify the complete host-to-dopant energy transfer and origin of the most intense red emission observed experimentally. Understanding the interplay of the experimental and theoretical results thus is a very useful general approach for improving the efficiency of luminescent materials.

Efficient Blue-emitting Phosphor SrLu2O4:Ce3+ with High Thermal Stability for Near Ultraviolet (~400 nm) LED-Chip based White LEDs

Blue-emitting phosphors for near ultraviolet (NUV) based tri-color RGB phosphor blend converted white light emitting diodes (LEDs) have been extensively investigated in the past few years. LED chip peaked near 400 nm is the most efficient among the NUV chips currently. However, most of blue phosphors show inefficient excitation around 400 nm. Herein, a novel blue phosphor SrLu2O4:Ce3+ matching well with near 400 nm chip and showing high thermal stability has been developed. The photoluminescence spectrum presents a broad emission band peaking at 460 nm with a bandwidth of nearly 90 nm. By optimizing the Ce3+ concentration, an internal quantum efficiency (IQE) as high as 76% was achieved. Furthermore, 86% of the room-temperature emission intensity is still maintained at 150 °C, indicating a good thermal stability and practicality. A series of white LEDs were fabricated based on 405 nm chips coated with a blend of the new blue phosphor with the commercial yellow and red phosphors. High color rendering indexes (≥90) were achieved while the correlated color temperature was tuneable in the range of 3094 to 8990 K. These results suggest that SrLu2O4:Ce3+ can be utilized as a blue-emitting phosphor in NUV based white LEDs.

Photonic structuring improves the colour purity of rare-earth nanophosphors

Nanophosphor integration in an optical cavity allows unprecedented control over both the chromaticity and the directionality of the emitted light, without modifying the chemical composition of the emitters or compromising their efficiency. Our approach opens a route towards the development of nanoscale photonics based solid state lighting.

Novel Eu3+-activated Ba2Y5B5O17 red-emitting phosphors for white LEDs: high color purity, high quantum efficiency and excellent thermal stability

Eu3+-activated Ba2Y5B5O17 (Ba2Y5-x Eu x B5O17; x = 0.1-1) red-emitting phosphors were synthesized by the conventional high temperature solid-state reaction method in an air atmosphere. Powder X-ray diffraction (XRD) analysis confirmed the pure phase formation of the as-synthesized phosphors. Morphological studies were performed using field emission-scanning electron microscopy (FE-SEM). The photoluminescence spectra, lifetimes, color coordinates and internal quantum efficiency (IQE) as well as the temperature-dependent emission spectra were investigated systematically. Upon 396 nm excitation, Ba2Y5-x Eu x B5O17 showed red emission peaking at 616 nm which was attributed to the 5D0 → 7F2 electric dipole transition of Eu3+ ions. Meanwhile, the influences of different concentrations of Eu3+ ions on the PL intensity were also discussed. The optimum concentration of Eu3+ ions in the Ba2Y5-x Eu x B5O17 phosphors was found to be x = 0.8. The concentration quenching mechanism was attributed to the dipole-dipole interaction and the critical distance (R c) for energy transfer among Eu3+ ions was determined to be 5.64 Å. The asymmetry ratio [(5D0 → 7F2)/(5D0 → 7F1)] of Ba2Y4.2Eu0.8B5O17 phosphors was calculated to be 3.82. The fluorescence decay lifetimes were also determined for Ba2Y5-x Eu x B5O17 phosphors. In addition, the CIE color coordinates of the Ba2Y4.2Eu0.8B5O17 phosphors (x = 0.653, y = 0.345) were found to be very close to the National Television System Committee (NTSC) standard values (x = 0.670, y = 0.330) of red emission and also showed high color purity (∼94.3%). The corresponding internal quantum efficiency of the Ba2Y4.2Eu0.8B5O17 sample was measured to be 47.2%. Furthermore, the as-synthesized phosphors exhibited good thermal stability with an activation energy of 0.282 eV. The above results revealed that the red emitting Ba2Y4.2Eu0.8B5O17 phosphors could be potential candidates for application in near-UV excited white light emitting diodes.

Characterization of Luminescent Materials with 151Eu Mössbauer Spectroscopy

The application of Mössbauer spectroscopy to luminescent materials is described. Many solids doped with europium are luminescent, i.e., when irradiated with light they emit light of a longer wavelength. These materials therefore have practical applications in tuning the light output of devices like light emitting diodes. The optical properties are very different for the two possible valence states Eu 2 + and Eu 3 + , the former producing ultraviolet/visible light that shifts from violet to red depending on the host and the latter red light, so it is important to have a knowledge of their behavior in a sample environment. Photoluminescence spectra cannot give a quantitative analysis of Eu 2 + and Eu 3 + ions. Mössbauer spectroscopy, however, is more powerful and gives a separate spectrum for each oxidation state enabling the relative amount present to be estimated. The oxidation state can be identified from its isomer shift which is between - 12 and - 15 mm/s for Eu 2 + compared to around 0 mm/s for Eu 3 + . Furthermore, within each oxidation state, there are changes depending on the ligands attached to the europium: the shift is more positive for increased covalency of the bonding ligand X, or Eu concentration, and decreases for increasing Eu⁻X bond length.

Neutralizing the Charge Imbalance Problem in Eu3+-Activated BaAl2O4 Nanophosphors: Theoretical Insights and Experimental Validation Considering K+ Codoping

In recent years, rare-earth-doped nanophosphors have attracted great attention in the field of luminescent materials for advanced solid-state lighting and high-resolution display applications. However, the low efficiency of concurrent red phosphors creates a major bottleneck for easy commercialization of these devices. In this work, intense red-light-emitting K⁺-codoped BaAl₂O₄:Eu³⁺ nanophosphors having an average crystallite size of 54 nm were synthesized via a modified sol-gel method. The derived nanophosphors exhibit strong red emission produced by the ⁵D₀ → ⁷F _J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ upon UV and low-voltage electron beam excitation. Comparative photoluminescence (PL) analysis is executed for Eu³⁺-activated and K⁺-coactivated BaAl₂O₄:Eu³⁺ nanophosphors, demonstrating remarkable enhancement in PL intensity as well as thermal stability due to K⁺ codoping. The origin of this PL enhancement is also analyzed from first-principles calculations using density functional theory. Achievement of charge compensation with the addition of a K⁺ coactivator plays an important role in increasing the radiative lifetime and color purity of the codoped nanophosphors. Obtained results substantially approve the promising prospects of this nanophosphor in the promptly growing field of solid-state lighting and field emission display devices.

A strategy for realizing tunable luminescence and full-color emission in Sr3Gd2(Si3O9)2:Eu phosphors by introducing dual functional Mn2+

The introduced Mn²⁺ ion can act as both an activator and a structure regulator in the SGSO:Eu system to achieve full-color emission and tunable luminescence of SGSO:0.03Eu,Mn phosphors.

Eu3+-activated La2MoO6-La2WO6 red-emitting phosphors with ultrabroad excitation band for white light-emitting diodes

A series of novel Eu³⁺-activated La₂MoO₆-La₂WO₆ red-emitting phosphors have been successfully prepared by a citrate-assisted sol-gel process. Both photoluminescence excitation and emission spectra suggest that the resultant products have the strong ultrabroad absorption band ranging from 220 to 450 nm. Under the excitation of 379 nm, the characteristic emissions of Eu³⁺ ions corresponding to the ⁵D₀ → ⁷F_J transitions are observed in the doped samples. The optimal doping concentration for Eu³⁺ ions is found to be 12 mol% and the quenching mechanism is attributed to the dipole-dipole interaction. A theoretical calculation based on the Judd-Ofelt theory is carried out to explore the local structure environment around the Eu³⁺ ions. The studied samples exhibit a typical thermal quenching effect with a T_0.5 value of 338 K and the activation energy is determined to be 0.427 eV. A near-ultraviolet (NUV)-based white light-emitting diode (LED) is packaged by integrating a mixture of resultant phosphors, commercial blue-emitting and green-emitting phosphors into an NUV LED chip. The fabricated LED device emits glaring white light with high color rendering index (84.6) and proper correlated color temperature (6492 K). These results demonstrate that the Eu³⁺-activated La₂MoO₆-La₂WO₆ compounds are a promising candidate for indoor lighting as red-emitting phosphors.

Facile microwave synthesis of ScPO4·2H2O flowerlike superstructures: morphology control, electronic structure and multicolor tunable luminescent properties

ScP0₄·2H₂O flowerlike superstructures constructed by well-aligned nanorods were prepared and multicolor tunable emission including white light emission was realized by adjusting the relative doping concentration.