Search Results (90)

In this work, a precursor-driven tailoring of strontium aluminate phosphors doped with Eu²⁺ and Dy³⁺ to generate unique, batch-specific luminescent signatures suitable for smartphone-detectable anti-counterfeiting tags was developed. A microwave-assisted hydrothermal synthesis approach was employed to explore the impact of a wide range of alkaline hydroxide and carbonate precursors on the structure of strontium aluminate. The resulting materials exhibited distinct differences in crystalline phase composition, morphology, and trap depth distribution. A smartphone-based detection system was developed, enabling rapid identification of spectral fingerprints. This study demonstrates a viable strategy for embedding unique luminescent identifiers, offering a scalable solution for robust, low-cost anti-counterfeiting applications in both the spectral and the time domain. Full article

In recent years, rare earth ion and transition metal ion co-doped fluorescent materials have attracted a lot of attention in the fields of WLEDs and optical temperature sensing. In this study, I successfully prepared the dual-emission Mg₃Ga₂SnO₈:Eu³⁺,Mn⁴⁺ red phosphors and the XRD patterns and refinement results show that the prepared phosphors belong to the Fd-3m space group. The energy transfer process between Eu³⁺ and Mn⁴⁺ was systematically investigated by emission spectra and decay curves of Mg₃Ga₂SnO₈:0.12Eu³⁺,yMn⁴⁺ (0.002 ≤ y ≤ 0.012) phosphors and the maximum value of transfer efficiency can reach 71.2%. Due to the weak thermal quenching effect of Eu³⁺, its emission provides a stable reference for the rapid thermal quenching of the Mn⁴⁺ emission peak, thereby achieving good temperature measurement performance. The relative thermometric sensitivities of the fluorescence intensity ratio and fluorescence lifetime methods reached a maximum value of 2.53% K⁻¹ at 448 K and a maximum value of 3.38% K⁻¹ at 473 K. In addition, the prepared WLEDs utilizing Mg₃Ga₂SnO₈:0.12Eu³⁺ phosphor have a high color rendering index of 82.5 and correlated color temperature of 6170 K. The electroluminescence spectrum of the synthesized red LED device by Mg₃Ga₂SnO₈:0.009Mn⁴⁺ phosphor highly overlaps with the absorption range of the phytochrome P_FR and thus can effectively promote plant growth. Therefore, the Mg₃Ga₂SnO₈:Eu³⁺,Mn⁴⁺ phosphors have good application prospects in WLEDs, temperature sensing, and plant growth illumination. Full article

Red melilite structure CaY_1−xAl₃O₇: Eu_x (x = 0.04–0.24) phosphors for white LEDs were synthesized through a straightforward solid-state reaction process. These phosphors exhibit efficient excitation under near-ultraviolet light at 398 nm (⁷F₀ → ⁵L₆), producing the desired emission peak at 622 nm from the transitions of ⁵D₀ → ⁷F₂. The Eu doping concentration was also optimized as x = 0.16. The complete 3003 × 3003 energy matrix was constructed based on an effective Hamiltonian including both free-ion and crystal-field interactions within a complete diagonalization method (CDM). Eighteen experimental fluorescent spectra for Eu³⁺ ions at the Y³⁺ site of CaYAl₃O₇ crystal were quantitatively identified with high accuracy through fitting calculations. The fitting values are in reasonable agreement with the experimental results, thereby showcasing the efficacy of the CDM in probing luminescent phosphors for white LEDs. Full article

The co-precipitation method was successfully used to synthesize Ba₃(Y_0.6−xGd_0.4Eu_x)₄O₉ (0.01 ≤ x ≤ 0.09) phosphors with heavy Gd³⁺ doping, resulting in significantly enhanced thermal stability and luminescence performance. Structural analyses confirm that Gd³⁺ and Eu³⁺ ions substitute Y³⁺ in the lattice, causing lattice expansion and improving crystal asymmetry, which enhances Eu³⁺ emission. The incorporation of Gd³⁺ creates efficient energy transfer pathways to Eu³⁺ while suppressing non-radiative relaxation, leading to stable fluorescence lifetimes even at elevated temperatures. With a thermal activation energy of ~0.3051 eV, the Ba₃(Y_0.55Gd_0.4Eu_0.05)₄O₉ phosphor exhibits superior resistance to thermal quenching compared to Ba₃(Y_0.95Eu_0.05)₄O₉ and many conventional red phosphors. Furthermore, the reduced color temperature and stable emission spectra across a wide temperature range highlight its potential for advanced lighting and display technologies in high-temperature environments. Full article

Using the solid-state reaction technique, varied Y₂SiO₅ phosphors activated by europium (Eu³⁺) ions at varied concentrations were made at calcination temperatures of 1000 °C and 1250 °C during sintering in an air environment. The XRD technique identified the monoclinic structure, and the FTIR technique was used to analyze the generated phosphors. Photoluminescence emission and excitation patterns were measured using varying concentrations of Eu³⁺ ions. The optimal strength was observed at a 2.0 mol% concentration. Emission peaks were detected at 582 nm and 589 nm for the ⁵D₀→⁷F₁ transition and at 601 nm, 613 nm, and 632 nm for the ⁵D₀→⁷F₂ transition under 263 nm excitation. Because Eu³⁺ is naturally bright, these emission peaks show how ions change from one excited state to another. This makes them useful for making phosphors that emit red light for use in optoelectronics and flexible displays. Based on the computed (1931 CIE) chromaticity coordinates for the photoluminescence emission spectra, it was determined that the produced phosphor may be used in light-emitting diodes. The TL glow curve was examined for various doping ion concentrations and durations of UV exposure levels, revealing a broad peak at 183 °C. Using computerized glow curve deconvolution (CGCD), we calculated the kinetic parameters. Full article

Novel Eu³⁺-doped Na₅Zn₂Gd(MoO₄)₆ triple molybdate phosphors were fabricated by the sol-gel method. The structure, morphology, and luminescent properties have been characterized by X-ray diffraction (XRD), thermogravimetric differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), FTIR spectroscopy, and luminescence spectroscopy. The results indicated that the synthesized Na₅Zn₂Gd_1−x(MoO₄)₆: xEu³⁺ phosphor consisted of a pure phase with monoclinic structure. Under excitation at 465 nm, the Na₅Zn₂Gd_1−x(MoO₄)₆: xEu³⁺ phosphor exhibits an intensive red emission band around 610 nm corresponding to the transition of ⁵D₀→⁷F₂ which is much higher than that ⁵D₀→⁷F₁ at 594 nm, which was appropriate for a blue LED. According to the influence of the synthesis conditions, the phosphors showed the highest emission intensity when the doping concentration of Eu³⁺ was 25 mol.% and the molar ratio of citric acid to metal ions was 2:1. Na₅Zn₂Gd_0.75(MoO₄)₆: 0.25 Eu³⁺ with the color coordinates (x = 0.658, y = 0.341) is a more stable red phosphor for blue-based white LEDs than the commercial Y₂O₂S: Eu³⁺ red phosphor (0.48, 0.50) due to its being closer to the NTSC standard values (0.670, 0.330). Full article

Detailed analysis covered the optical and structural properties of Eu³⁺-doped NaY₉Si₆O₂₆ oxyapatite phosphors, which were obtained via hydrothermal synthesis. X-ray diffraction patterns of NaY₉Si₆O₂₆:xEu³⁺ (x = 0, 1, 5, 7, 10 mol% Eu³⁺) samples proved a single-phase hexagonal structure (P63/m (176) space group). Differential thermal analysis showed an exothermic peak at 995 °C attributed to the amorphous to crystalline transformation of NaY₉Si₆O₂₆. Electron microscopy showed agglomerates composed of round-shaped nanoparticles ~53 nm in size. Room temperature photoluminescent emission spectra consisted of emission bands in the visible spectral region corresponding to ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) f-f transitions of Eu³⁺. Lifetime measurements showed that the Eu³⁺ concentration had no substantial effect on the rather long ⁵D₀-level lifetime. The Eu³⁺ energy levels in the structure were determined using room-temperature excitation/emission spectra. Using the ⁷F₁ manifold, the Nv-crystal field strength parameter was calculated to be 1442.65 cm⁻¹. Structural, electronic, and optical properties were calculated to determine the band gap value, density of states, and index of refraction. The calculated direct band gap value was 4.665 eV (local density approximation) and 3.765 eV (general gradient approximation). Finally, the complete Judd–Ofelt analysis performed on all samples confirmed the experimental findings. Full article

Tunable blue/red dual-emitting Eu³⁺-doped, Bi³⁺-sensitized SrF₂ phosphors were synthesized utilizing a solvothermal-microwave method. All phosphors have cubic structure (Fm-3m (225) space group) and well-distinct sphere-like particles with a size of ~20 nm, as examined by X-ray diffraction and transmission electron microscopy. The diffuse reflectance spectra reveal a redshift of the absorption band in the UV region as the Bi³⁺ concentration in SrF₂: Eu³⁺ phosphor increases. Under the 265 nm excitation, photoluminescence spectra show emission at around 400 nm from the host matrix and characteristic orange ⁵D₀ → ⁷F_1,2 and deep red ⁵D₀ → ⁷F₄ Eu³⁺ emissions. The red emission intensity increases with an increase in Bi³⁺ concentration up to 20 mol%, after which it decreases. The integrated intensity of Eu³⁺ red emission in the representative 20 mol% Bi³⁺ co-doped SrF₂:10 mol% Eu³⁺ shows twice as bright emission compared to the Bi³⁺-free sample. To demonstrate the potential application in LEDs for artificial light-based plant factories, the powder with the highest emission intensity, SrF₂: 10Eu, 20 Bi, was mixed with a ceramic binder and placed on top of a 275 nm UVC LED chip, showing pinkish violet light corresponding to blue (409 nm) and red (592, 614, and 700 nm) phosphors’ emission. Full article

Novel multicomponent glasses with nominal compositions of (50−x)MoO₃:xWO₃:25La₂O₃:25B₂O₃, x = 0, 10, 20, 30, 40, 50 mol% doped with 3 mol % Eu₂O₃ were prepared using a conventional melt-quenching method. Their structure, thermal behavior and luminescent properties were investigated by Raman spectroscopy, differential thermal analysis and photoluminescence spectroscopy. The optical properties of the glasses were investigated by UV–vis absorption spectroscopy and a determination of the refractive index. Physical parameters such as density, molar volume, oxygen molar volume and oxygen packing density were determined. The glasses are characterized by a high glass transition temperature. Raman analysis revealed that the glass structure is built up mainly from tetrahedral (MoO₄)²⁻ and (WO₄)²⁻ units providing Raman bands of around 317 cm⁻¹, 341–352 cm⁻¹, 832–820 cm⁻¹ and 928–935 cm⁻¹. At the same time, with the replacement of MoO₃ with WO₃ some fraction of WO₆ octahedra are produced, the number of which increases with the increasing WO₃ content. A strong red emission from the ⁵D₀ level of Eu³⁺ ions was registered under near-UV (397 nm) excitation using the ⁷F₀ → ⁵L₆ transition of Eu³⁺. Photoluminescence (PL) emission gradually increases with increasing WO₃ content, evidencing that WO₃ is a more appropriate component than MoO₃. The integrated fluorescence intensity ratio R (⁵D₀ → ⁷F₂/⁵D₀ → ⁷F₁) was calculated to estimate the degree of asymmetry around the active ion, suggesting a location of Eu³⁺ in non-centrosymmetric sites. All findings suggest that the investigated glasses are potential candidates for red light-emitting phosphors. Full article

This manuscript describes the synthesis of green long afterglow nanophosphors SrAl₂O₄:Eu²⁺, Nd³⁺ using the combustion process. The study encompassed the photoluminescence behavior, elemental composition, chemical valence, morphology, and phase purity of SrAl₂O₄:Eu²⁺, Nd³⁺ nanoparticles. The results demonstrate that after introducing Eu²⁺ into the matrix lattice, it exhibits an emission band centered at 508 nm when excited by 365 nm ultraviolet light, which is induced by the 4f⁶5d¹→4f⁷ transition of Eu²⁺ ions. The optimal doping concentrations of Eu²⁺ and Nd³⁺ were determined to be 2% and 1%, respectively. Based on X-ray diffraction (XRD) analysis, we have found that the physical phase was not altered by the doping of Eu²⁺ and Nd³⁺. Then, we analyzed and compared the quantum yield, fluorescence lifetime, and afterglow decay time of the samples; the co-doped ion Nd³⁺ itself does not emit light, but it can serve as an electron trap center to collect a portion of the electrons produced by the excitation of Eu²⁺, which gradually returns to the ground state after the excitation stops, generating an afterglow luminescence of about 15 s. The quantum yields of SrAl₂O₄:Eu²⁺ and SrAl₂O₄:Eu²⁺, Nd³⁺ phosphors were 41.59% and 10.10% and the fluorescence lifetimes were 404 ns and 76 ns, respectively. In addition, the E_g value of 4.98 eV was determined based on the diffuse reflectance spectra of the material, which closely matches the calculated bandgap value of SrAl₂O₄. The material can be combined with polyacrylic acid to create optical anti-counterfeiting ink, and the butterfly and ladybug patterns were effectively printed through screen printing; this demonstrates the potential use of phosphor in the realm of anti-counterfeiting printing. Full article

Garnet-type materials consisting of Y₃Al_5-2x(Mg,Ge)_xO₁₂ (x = 0, 1, 2), combined with Eu³⁺ or Ce³⁺ activator ions, were prepared by a solid-state method to determine the structural and optical correlations. The structure of Y₃Al_5-2x(Mg,Ge)_xO₁₂ (x = 1, 2) was determined to be a cubic unit cell (Ia-3d), which contains an 8-coordinated Y³⁺ site with octahedral (Mg,Al)O₆ and tetrahedral (Al,Ge)O₄ polyhedra, using synchrotron powder X-ray diffraction. When Eu³⁺ or Ce³⁺ ions were substituted for the Y³⁺ site in the Y₃Al_5-2x(Mg,Ge)_xO₁₂ host lattices, the emission spectra showed a decrease in the magnetic dipole f-f Eu³⁺ transition and a redshift of the d-f Ce³⁺ transition, related to centrosymmetry and crystal field splitting, respectively. These changes were monitored according to the increase in Mg²⁺ and Ge⁴⁺ contents. The dodecahedral and octahedral edge sharing was identified as a key distortion factor for the structure-correlated luminescence in the Eu³⁺/Ce³⁺-doped Y₃Al_5-2x(Mg,Ge)_xO₁₂ garnet phosphors. Full article

In this work, we investigated the potential of Eu³⁺/Dy³⁺-codoped Y₂Sn₂O₇ fluorescent nanophosphors to visualize latent fingermarks. We prepared these nanophosphors with various doping concentrations by the conventional coprecipitation reaction. The crystal structure, morphology, luminescence properties, and energy transfer mechanisms were studied. The crystalline phase was characterized by X-ray diffraction and crystal structure refinement using the Rietveld method. XRD measurements showed that the samples crystallized in the pure single pyrochlore phase with few more peaks originated from secondary phases and impurities generated during phosphor production, and that Eu³⁺ ions occupied D_3d symmetry sites. The average crystallite size after mechanical grinding was less than 100 nm for all compositions. The optical characterization showed that, when excited under 532 nm, the Eu³⁺/Dy³⁺-codoped Y₂Sn₂O₇ samples’ main intense emission peaks were located at 580–707 nm, corresponding to the ⁵D₀→⁷Fj (j = l, 2, 3, and 4) transitions of europium. In fact, the ⁵D₀→⁷F₂ hypersensitive transition is strongly dependent on the local environment and was quite weak in Eu³⁺:Y₂Sn₂O₇ at low Eu³⁺ doping levels. We found that the presence of Dy³⁺ as a codopant permitted enhancing the emission from this transition. The calculated PL CIE coordinates for the synthesized nanophosphors were very close to those of the reddish-orange region and only slightly dependent on the doping level. Various surfaces, including difficult ones (wood and ceramic), were successfully tested for latent fingerprint development with the prepared Eu³⁺/Dy³⁺-codoped Y₂Sn₂O₇ fluorescent nanophosphor powder. Thanks to the high contrast obtained, fingerprint ridge patterns at all three levels were highlighted: core (level 1) islands, bifurcation, and enclosure (level 2), and even sweat pores (level 3). Full article

A new series of Sr-based phosphates, Sr_9−xMn_xEu(PO₄)₇, were synthesized using the high-temperature solid-state method in air. It was found that these compounds have the same structure as strontiowhitlockite, which is a β-Ca₃(PO₄)₂ (or β-TCP) structure. The concentration of Mn²⁺ ions required to form a pure strontiowhitlockite phase was determined. An unusual partial reduction of Eu³⁺ to Eu²⁺ in air was observed and confirmed by photoluminescence (PL) and electron spin resonance (ESR) spectra measurements. The PL spectra recorded under 370 nm excitation showed transitions of both 4f5d–4f Eu²⁺ and 4f–4f Eu³⁺. The total integral intensity of the PL spectra, monitored at 395 nm, decreased with increasing Mn²⁺ concentration due to quenching effect of Eu³⁺ by the Mn²⁺ levels. The temperature dependence of Eu²⁺ photoluminescence in a Sr_9−xMn_xEu(PO₄)₇ host was investigated. The conditions for the reduction of Eu³⁺ to Eu²⁺ in air were discussed. Full article

In this work, solid-state reaction sintering was used to fabricate Ca₇ZrAl₆O₁₈-Ca₃Al₂O₆-CaZrO₃:Eu³⁺ ternary composite ceramics and cements. The structural, microstructural, and spectroscopic properties of the ceramics with different Eu₂O₃ content were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), and spectrofluorimetry, respectively. The XRD patterns analyzed with Rietveld refinement confirm the presence of the orthorhombic phase of Ca₇ZrAl₆O₁₈ and the cubic phase of Ca₃Al₂O₆ in all the samples, indicating that doping of Eu³⁺ slightly changes the crystalline structure of both aluminate phosphors. EDS analysis revealed that the Eu doping element was strongly concentrated to the two phases, i.e., Ca₇ZrAl₆O₁₈ and Ca₃Al₂O₆, with the Eu concentrations of 8.45 wt.% and 8.26 wt.%, respectively. The luminescent properties of the ceramics doped with different Eu³⁺ ion concentrations were investigated by excitation and emission spectroscopy at room temperature. These results were compiled using a laser with an optical parametric oscillator (OPO) system. The obtained spectra indicated changes in the luminescence intensity and shape occurring with phase composition and Eu₂O₃ concentration. The emission spectra of the ceramics exhibit a strong dependence on the excitation wavelength in the range from 210 to 300 nm, and invariably, five peaks were assigned to the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺. The luminescence spectroscopy was then used to trace the early and long-term hydration behavior of cements. Thus, luminescence spectroscopy may provide a new tool for non-destructive testing of cement-based structures. Full article

In this study, we investigated the influence of Bi₂O₃ and WO₃ on both structure and optical properties of 50ZnO:(49 − x)B₂O₃:1Bi₂O₃:xWO₃; x = 1, 5, 10 glasses doped with 0.5 mol% Eu₂O₃. IR spectroscopy revealed the presence of trigonal BØ₃ units connecting superstructural groups, [BØ₂O]⁻ metaborate groups, tetrahedral BØ₄⁻ units in superstructural groupings (Ø = bridging oxygen atom), borate triangles with nonbridging oxygen atoms, [WO₄]²⁻ tetrahedral, and octahedral WO₆ species. Neutron diffraction experimental data were simulated by reverse Monte Carlo modeling. The atomic distances and coordination numbers were established, confirming the short-range order found by IR spectra. The synthesized glasses were characterized by red emission at 612 nm. All findings suggest that Eu³⁺ doped zinc borate glasses containing both WO₃ and Bi₂O₃ have the potential to serve as a substitute for red phosphor with high color purity. Full article