Racah Parameters Research Articles

Asperomagnetism and speromagnetism in magnetic aluminosilicate glasses

In this research, we make use of mineral waste composite with elemental composition of Si, Al, Ca, Mg, K and Fe to synthesize magnetic aluminosilicate glasses (MAGlass). The produced MAGlass presented interesting magnetic and optical properties due to the presence of iron with different valence states. The elemental composition was measured by X-ray fluorescence spectroscopy. X-ray diffraction analysis confirmed the glass amorphous nature. Thermal properties such as glass transition temperature and thermal stability were analyzed by differential scanning calorimetry. The nature of the glass chemical bond structure was studied by FT-Raman analysis. UV–Vis spectroscopy studied the transmittance and absorbance in each sample, approaching the main electronic transitions, Racah parameters and gap energy. Mössbauer and magnetization measurements showed different iron valency states and interesting asperomagnetism and speromagnetism behaviors, with variations among the Fe2＋ and Fe2.5+ in the MAGlass samples.

Impact of SnO2 doping on spectroscopic characteristics of the SnO2-Na2O-CoO-B2O3 borate glass matrix

The role of tin oxide (SnO2) on the structure-optical features of borate glasses containing low cobalt oxide impurities was studied. The study was carried out on a glass system [x SnO2 – (80-x) B2O3 – 19.5 Na2O – 0.5 CoO]; x = 0.0, 0.5, 1.0, 2.0 and 3.0 mol%. Glass synthesis was carried out by the melt-quench technique. Structure and optical absorption spectroscopy were carried out to explore the optical transitions of Co cations inside the present glass matrix. The obtained results indicate that, with the further addition of SnO2 content, the molar volume decreased from 31.675 cm3/mol to 29.147 cm3/mol. FTIR studies indicated the basic structural units of trigonal BO3 units and BO4 tetrahedra. Herein also, additional contents of tin oxide increased the nonbridging oxygen contents. The reason behind such increment is attributed to the existence of Sn4+ ions in octahedral coordination acting as network modifiers. Optical absorption spectra indicated the existence of Co ions in both Co2+ and Co3+ oxidation states. Moreover, the existence of significant SnO2 concurred with the significant blue shift in the visible absorption bands and red shift in near infrared absorption bands. The positions absorption bands of Co ions were analyzed in the context of ligand field parameters determinations. The obtained data of the crystal field splitting parameter (10Dqt) showed decreased values from 3451 cm−1 to 3364 cm−1 with more SnO2 addition. While Racah parameter B values were also, attained showing increased values from 967 cm−1 to 985 cm−1 when additional SnO2 is added. Further, the impacted role of SnO2 addition on the structural and optical properties of the present glasses was finally estimated.

Exploring the structural and optical properties of lithium-chromium phosphate Li3Cr2(PO3)4

The Lithium-chromium phosphate Li3Cr2(PO3)4 sample was synthesized via the solid-state reaction method. The morphological integrity and chemical homogeneity were verified by energy dispersive X-ray analysis (EDX) and scanning electron microscopy (SEM). Infrared and Raman patterns were also analyzed. Optical absorption spectrum analysis, conducted within the range of 10000 cm−1 to 30000 cm−1 at room temperature, yielded some optical parameters (Eg, Eu, δ, k, n). The Neuhauser model is used to interpret the interference dip which was on the absorption spectrum of Li3Cr2(PO3)4. The Fourier transform of the autocorrelation function leads to the Zero Phonon Lines of the observed absorption energies. The electronic structure of Cr3+ (3d (Huang et al., 2009) 33) ions in Li3Cr2(PO3)4 was calculated using Racah method, which allowed for precise calculations of Racah and crystal-field parameters. The results showed good agreement between the theoretical and experimental energy levels.

Controllable morphology, excellent stability and non-equivalent doping-induced optical properties of Mn4+-activated K2NaScF6 red phosphor for high-quality warm WLED

Currently, Mn4+ activated fluoride red phosphor has been widely studied to improve the optical performance of white light-emitting diode (WLED) in the field of high-efficiency lighting and wide color gamut backlight display. In this paper, a series of red-emitting K2NaScF6:Mn4+ phosphors are synthesized by a simple co-precipitation method with a non-equivalent substitution of Mn4+ for Sc3+ at room temperature. The crystal structure, morphology and elemental composition of K2NaScF6:Mn4+ phosphors prepared using different reaction conditions are systematically investigated. Interestingly, the K2NaScF6:Mn4+ phosphors exhibit narrowband red emission with low correlated color temperature (CCT), high color purity and short fluorescence lifetime. Compared to equivalent doping, the mechanism of short fluorescence lifetime caused by non-equivalent doping has also been systematically discussed. The optimal doping concentration is determined by setting a series of Mn4+ doping concentrations and the concentration quenching mechanism is analyzed. The crystal field strength (Dq), Racah parameters (B and C) and nephelauxetic ratio (β1) are calculated in detail to evaluate the crystal field environment of Mn4+ in K2NaScF6. The good water resistance of the as-prepared sample K2NaScF6:Mn4+ is verified by comparing with the commercially available phosphor K2SiF6:Mn4+. Moreover, the thermal stability is also analyzed by calculating the activation energy (Ea), chromaticity shift (ΔE) and chromaticity coordinate variation (CCV). Importantly, the as-packaged warm WLED (InGaN chip + YAG:Ce3+ + K2NaScF6:Mn4+) has excellent optical properties (CCT = 4082 K, color rendering index (CRI, Ra = 91.2) and luminous efficiency (LE) = 78.86 lm/W), and it exhibits good output stability at high drive currents. In summary, our work demonstrates that K2NaScF6:Mn4+ red phosphors possess a great potential application in warm WLED for the indoor lighting.

LaBaMg(Ti0.5W0.5)O6:Mn4+ for plant growth lighting: Luminescence properties and synthesis

With the need of food safety and high yield, new luminescent materials with promoting plant photosynthesis have attracted more and more attention. In this research, we synthesize the far-red-emitting LaBaMg(Ti0.5W0.5)O6:Mn4+ phosphor in air. We investigate the crystal structure and phase, particle morphology and size, and the luminescence properties. The samples show a broad excitation spectrum under monitored 704 nm due to the Mn4+ - O2− charge transfer (CT) and the transitions 4A2g → 4T1g, 2T2g, and 4T2g of Mn4+ in the range of 300 – 600 nm. The far-red emission of sample is observed with the emission spectrum (650 – 790 nm) is attributed to the Eg → 4A2g transitions. The chromaticity coordinates are (0.7329, 0.2671). The crystal field strength (Dq), the Racah parameters (B and C), and Dq/B values are ∼ 1972 cm−1, 596 cm−1, 3219 cm−1, and 3.31, respectively. 0.2 mol% is the optimal Mn4+ concentration. Emission spectra under excitation wavelength from 320 nm to 560 nm and time-resolved emission spectra confirm the only luminous center (Mn4+) in LaBaMg(Ti0.5W0.5)O6:Mn4+. Lifetime reduces with added Mn4+ concentration. The temperature-dependence emission spectra confirm that sample has a good thermo-stability. The thermal quenching phenomenon and luminous mechanism are analyzed. The luminescence properties of sample infer its application prospect in plant growth light-emitting diode (LED).

Optical and EPR spectroscopy of manganese doped LiNaGe4O9 single crystals

The paper presents data on the study of optical absorption, photoluminescence and EPR of lithium-sodium tetragermanate crystals (LiNaGe4O9) doped with Mn ions. Optical spectra were measured in the range 11000–45000 cm−1 and temperatures 77–300 K. They are attributed to manganese in the +4 charge state. From the analysis of optical spectra, the crystal field strength Dq = 2175.2 cm−1 and Racah parameters A = 4065 cm−1, B = 813 cm−1, C = 3239 cm−1 were determined for the Mn4+ ions. The value of the Huang-Rhys factor SFHR = 17.56 indicates a strong electron-phonon interaction of the Mn4+ ion. The presence of Mn4+ ions was further confirmed by measurement of EPR spectra at microwave frequencies 8.9 and 320 GHz. EPR data show that Mn4+ ions occupy two structurally nonequivalent lattice sites with the formation of two Mn4+ centers: Mn1 and Mn2. From the angular dependences of the EPR spectra, the components of the g factor and the hyperfine interaction tensor A, the parameters of the axial D and rhombic E crystal field were determined for both centers. The axial constant D is large for both centers: 0.644 and 0.560 cm−1, respectively. Analysis of optical and EPR spectroscopic data testifies that Mn4+ ions replace the Ge4+ ions in oxygen octahedrons within the host. Structurally nonequivalent centers are attributed to manganese ions located in undistorted lattice sites (Mn1) and in sites perturbed by the LiNa antisite defect (Mn2).

Understanding the multiplet fine structures of MgO: Cr3+ with combination method of first−principles calculations and ligand field theory

The interpretative and predictive capabilities on the energy fine structures of transition metal ions in solids are explored by integrating the first -principles calculations with ligand-field (LF) theory. The charge-compensated site of MgO: Cr3+ is chosen as a case and the aim is to determine the energy-level fine structure and EPR g factor g// and g⊥. The approach involves initially computing all the required parameters for LF theory through first-principles calculations, and these parameters are subsequently fed into the LF model Hamiltonian, which fully incorporates interactions between different spectrum terms through the LF operator, spin-orbit coupling (SOC) operator and other relevant factors. The calculated zero-field splitting parameter D and g factors of the ground term A24(t23) are reasonably good agreement with the experimental observations. However, the energy levels of excited states are slightly underestimated compared to experimental values due to the underestimation of Racah parameters in the first-principles calculations, except the T24[t22(T13)e] term which is insensitive to Racah parameters for it is equal to 10Dq relative to ground term A24(t23) with possible minor corrections due to perturbations.

Practical consideration on Racah parameter and Tanabe−Sugano diagram analyses for Mn4+ and Cr3+-activated phosphors

The Racah parameters and Tanabe−Sugano (T−S) diagram are widely used as describing the electron−electron repulsion effects within the metal complexes in coordination chemistry. The present study discusses the Racah and related parameters for the Mn4+ and Cr3+-activated phosphors. The main subjects are two-fold: (i) to clarify how different input parameters of the excited-state energies make a difference in the Racah parameters derived from the general model and (ii) to further clarify the differences between the general and our newly proposed models. The three different excited-state energies of (1) the zero-phonon line energy, (2) the photoluminescence (PL) and/or PL excitation (PLE) peak energies, and (3) the Stokes shift-corrected PLE peak energy are considered in (ii). It is shown that the choice of such excited-state energies is of crucial importance for obtaining reliable Racah parameters and T−S diagram. The present analysis of (ii) also suggests our newly proposed model to promise the Racah parameters being satisfied the requirements of B and C to be smaller than and their ratio of C/B being not largely changed from the free-ion values. The lattice temperature effects on the PL and PLE spectral features of the 3d3 ion-activated phosphors are also discussed in detail.

Narrowband red luminescence of tetrahedral-site Fe3+ In Ca8Mg(SiO4)4Cl2

We have measured the excitation and emission spectra, and lifetime for Fe3+ in the Ca8Mg(SiO4)4Cl2 compound. The spectroscopic data of the ferric ion (Fe3+) is interpreted within the framework of the Tanabe-Sugano crystal field theory for ions with the d5 electronic configuration. Quantitative evaluation of the Racah parameters B and C and the crystal field parameter (10 Dq) is provided. The emission and excitation data are consistent for Fe3+ in a tetrahedral-site occupancy. The red emission is assigned to the 4T1 (4G)→6A1 (6S) crystal field transition. The remarkable feature of the luminescence is the positioning of the emission band; it is centered at 623 nm with a Full Width at Half Maximum of 51 nm. To the best of our knowledge this is one of the highest energy emission for the tetrahedral-site Fe3+ ion. The practical implication of this spectral power distribution is discussed. The temperature dependency of the luminescence lifetime and emission intensity are reported.

UV- and X-ray-activated broadband NIR garnet-type Ca3Ga2Sn3O12:Fe3+ phosphors with efficient persistent luminescence

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are compact light sources of great interest for NIR spectroscopy applications. Beyond typical Cr3+-activated NIR-emitting phosphors, there exists a strong demand for Cr3+-free alternatives with high efficiency and broadband emission to rich the landscape of NIR luminescent materials and extend their range of application fields. Here, we report a series of Fe3+-activated Ca3Ga2Sn3O12 garnet-type phosphors exhibiting broadband NIR emission in the 650–1000 nm range attributed to 4T1(G) → 6A1(S) transition, with a maximum at 754 nm and a FWHM of 89 nm upon UV excitation. The spectroscopic results were analyzed according to the Tanabe-Sugano theory from which the crystal field parameter Dq and Racah parameters B and C were obtained for the octahedrally coordinated Fe3+ ion. Notably, the NIR persistent luminescence lasting over 1 h was detected following UV or X-ray irradiation. The possible mechanism involving electron traps was proposed to explain the observed persistent luminescence. Furthermore, a NIR pc-LED was fabricated by coating synthesized phosphor on a UV chip, and its performance was evaluated to assess its potential suitability as a NIR light source. Our discovery of novel type of nontoxic Fe3+-activated broadband NIR luminescence phosphors with efficient NIR persistent luminescence paves the way for discovering Cr3+-free multifunctional NIR luminescence materials, thereby expanding their application possibilities.

Impact of mixed heavy metal cations (Ba and Bi) on the structure, optical and ionizing radiation shielding parameters of Bi2O3–BaO–Fe2O3–SrO–B2O3 glass matrix

The impacts of the Bi2O3/BaO ratio on the microstructure, optical, ligand field, and radiation shielding features of BSrFeBaBi glass matrix. The Bi2O3 content of the BSrFeBaBi glasses was increased from 0 to 20 mol%. The density increased from 3.77 g/cm3 to 5.00 g/cm3 and the molar volume increased from 24.74 cm3/mol to 31.17 cm3/mol with increasing Bi2O3/BaO ratio. The optical analysis confirmed that the transparency of BSrFeBaBi glasses in the visible region is high. Moreover, the presence of Fe cations in the octahedral coordination (FeO6 units) was confirmed. Furthermore, the fundamental absorption edge of BSrFeBaBi glasses shifts towards lower energies with additional Bi2O3/BaO concentrations, confirming the reduced behavior of the optical band gap. Also, ligand field splitting values decreased while Racah parameters increased. The obtained results demonstrate a tendency of the bonds between the Fe ions and their surroundings towards higher degree of ionic nature. Furthermore, the Bi2O3/BaO ratio demonstrated an enhanced radiation shielding behavior. Finally, BSrFeBaBi glasses exhibit favorable attributes for use in the radiation shielding domain due to their efficient radiation shielding features and transparency.

Mössbauer, optical and structural properties of [formula omitted] ion in borate glass

Lanthanum-bearing iron lithium borate glass is a quaternary system for oxide glasses and was prepared via the melt-quenching method. The present article correlates the structure, optical, ligand field and Mössbauer data on iron lithium borate glass containing La3+. The density was measured, while the molar volume was calculated. Other physical parameters are well-described. With increasing the La2O3 content within the glass network, infrared spectra analysis reveals structural modifications such as the increase in BO4 units and the decline in both BO3 units and NBO bonds content. Furthermore, optical absorption spectra were measured. The absorption spectra disclose a plethora of electronic transitions that are related to Fe3+ in tetrahedral and octahedral sites, however, Fe2+ phase is not observed in optical spectra, but it has a clear signature in Mössbauer spectra. Besides, the glass absorption edges undergo a clear blue shift, reflecting an increased band gap energy (1.96–2.28 eV). The decline in NBO bonds justifies this trend. Bewitchingly, the values of crystal field splitting are increased, while the values of Racah parameters are decreased. This trend is justified by the decline in NBO bonds and increases electron localization around Fe cations. Mössbauer spectra confirm the existence of Fe3+ in tetrahedral and octahedral sites, while Fe2+ exists in only a tetrahedral state. With increasing La2O3 content, the isomer shift of Fe3+ in tetrahedral sites changes to be 0.312–0.329 mm/s, while the isomer shift of octahedral Fe3+ is 0.424–0.456 mm/s. These findings coincide with optical data. While the isomer shift of tetrahedral Fe2+ is 0.902–0.911 mm/s. Our results of structural, optical and ligand field associated with Mössbauer spectra open more vistas toward the utility of these samples in the optics realm.

Host Dependency of Boundary between Strong and Weak Crystal Field Strength of Cr3+ Luminescence.

Cr3+ doped near-infrared phosphors hold significant applications and generate considerable research interest. The critical parameter for assessing the strength of the crystal field for Cr3+ in the Tanabe-Sugano diagram is the boundary value of Dq/B, representing the ratio of crystal field splitting to the Racah parameter B. Nevertheless, there are conflicting values for this parameter, as reported in various studies, such as 2.1, 2.2, and 2.3 for C/B = 4.5-4.8. Moreover, some Cr3+ doped phosphors with wide-band emissions exhibit a Dq/B value that falls within the region of a contradictory strong field. In this study, we numerically determine the boundary value of Dq/B, which distinguishes between strong and weak fields. The results then demonstrate a dependence on the host material and are correlated with the values of Racah parameters B and C. This work resolves the inconsistency between the boundary values of Dq/B and the emission profile of Cr3+, providing researchers with a more profound comprehension of Cr3+ luminescence.

Unveiling Local Electronic Structures of Manganese‐Doped Double Perovskites Red Emitters

AbstractOver the past few years, light‐emitting diodes (LEDs) have emerged as an efficient replacement for standard incandescent and fluorescent lamps, due to their superior efficiency, energy conservation, service longevity, reliability, and affordability. However, identifying a red emitter for white LEDs has presented significant challenges. This study seeks to synthesize and analyze a novel red emitter, investigating its potential use in white LEDs and indoor plant growth lighting. The Sr2Lu(Nb,Mn)O6 is manufactured employing the traditional high‐temperature solid‐phase method. The internal and external quantum efficiencies (IQE and EQE) of double perovskites reached 32.39% and 21.67%. The g value calculates to 2.146, which corroborates that the magnetic dipolar transitions of Mn4+ ions inhabit symmetric octahedral sites. First‐principles investigations are utilized to unveil local electronic structures. Emission spectra reveal a substantial broad red emission peak at 688 nm. The Tanabe–Sugano diagram is applied to understand the luminescence mechanism. Additionally, the evaluation of parameters such as the internal UV emission ratio, crystal field strength, and Racah parameters is conducted. The luminescent intensity of the Sr2Lu(Nb,Mn)O6 can still be maintained at 60% upon reaching a temperature of 423 K. The findings suggest that Sr2Lu(Nb,Mn)O6 offers a novel alternative for white LEDs and indoor plant growth lighting.

Structural and optical properties of Zn2.95Ga2−xSnO8:xCr3+: An excellent X-ray charging-based persistent phosphor

This study investigates structural and luminescence properties of Cr3+ doped Zn2.95Ga2SnO8 phosphor. XRD analysis determines the phase purity and lattice parameters, while SEM and TEM analysis were utilized to study the particle size and surface morphology of the sample. UV–visible absorption and PL excitation spectra provided information on the excitation bands and the band-gap of both the undoped and Cr3+ doped Zn2.95Ga2SnO8. The optical band-gap of the material decreases upon doping with Cr3+ ions. Analysis of the Racah parameter and Tanabe Sugano diagram highlights a robust crystal field within Cr3+: Zn2.95Ga2SnO8, causing 2Eg level to become the lowest excited state with sharp emission at 699 nm. Concentration quenching at higher Cr3+ concentrations (> 0.6 mol%) is primarily attributed to the quadrupole-quadrupole interactions. Two distinct traps with trap depths at 0.51 eV and 0.73 eV were identified by using thermoluminescence measurement. The material gives persistent luminescence with a decay time of more than 30 min when charged with blue light (420 nm) and an excellent decay time of more than 16 h when charged with X-rays. Notably, this is the first report on X-ray charging-based persistent luminescence in Zn2.95Ga2SnO8. The outstanding persistent luminescence makes this material highly promising for various applications.

Optical and theoretical study of NaCr(P2O7): a look through the Neuhauser model and Racah theory.

A sample of NaCr(P2O7) was synthesized using the solid-state reaction method. X-ray diffraction and Rietveld refinement confirmed the formation of a monoclinic structure with the P21/a space group. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis identified the morphology and homogeneity of the chemical composition. The optical absorption spectrum revealed a direct optical band gap of 2.9 eV and an Urbach energy of 0.44 eV. Notably, the absorption spectrum showed an interference dip on the lowest energy band 4T2g(4F), attributed to spin-orbit coupling between states 2Eg(2G) and 4T2g(4F). This phenomenon was analyzed using the Neuhauser model based on coupled potential energy surfaces. From this analysis, the electronic structure of Cr3+ (3d3) ions in the NaCr(P2O7) sample was determined, enabling a reliable calculation of Racah and crystal-field parameters. The results showed good agreement between experimental and theoretical energy levels. The study demonstrates the impact of spin-orbit interactions using the coupled potential energy surface model.

Impact of the As2O3/B2O3 ratio on the structure and optical features of As2O3–NiO–Na2O–B2O3 glass

The impact of the As2O3/B2O3 ratio on the microstructure, linear and nonlinear optical parameters of nickel borate glass was carefully investigated for the As2O3–NiO–Na2O–B2O3 system. The As2O3 content of the present glass were varied from 0 to 16 mol%, while the glass modifiers of Na2O and glass intermediate of NiO were fixed at 18 and 1 mol%, respectively. Based on the structural investigations, the density increased from 2.52 gcm−3 to 2.95 gcm−3 and the molar volume increased from 27.11 cm3.mol−1 to 30.07 cm3.mol−1 with increasing As2O3/B2O3 ratios. Additionally, the presence of Ni2+ ions as NiO6 units was confirmed by the brown color originating from the absorption band observed at 421–428 nm in the optical absorbance of the studied glass. Furthermore, the Ni3+ ions do not participate in the coloring of the glass. Moreover, the fundamental absorption edges of the glass shift towards lower energy values with increasing As2O3/B2O3 concentrations, confirming the decreased behavior of the band gaps. Furthermore, the nonlinear refractive index increases with the increased As2O3/B2O3 concentrations. Additionally, the ligand field parameters of Ni cations, such as the ligand field splitting parameter and Racah parameter, exhibit opposite behaviors upon introducing additional As2O3/B2O3 ratio. A decrease in values of the ligand field splitting, while the Racah parameter exhibits increased values. The observed outcomes demonstrate a tendency of the bonds connecting the Ni ions and their ligands to possess higher degrees of ionic nature. Besides, the ionizing radiation properties for the prepared glasses were studied using online “Phy-X″ software in the energy range of 0.248–1.33 MeV. The ionizing radiation shielding invistigations showed enhanced parameters with further As2O3 additives. Where, with increasing the amount of As2O3 from 0 mol% to 16 mol%, there are increases in the mass attenuation coefficient values. Additionally, the half value layer values of the studied glass samples are lower than the values of most standard ionizing radiation shielding materials. The effective As2O3/ B2O3 ratio enhanced structure, optical and radiation shielding parameters of the present glass system, making these glasses suitable for ionizing radiation shielding applications.

Synthesis, optical characteristics and thermal stability of Mn4+-doped Na3GaF6 red-emitting phosphor for high-performance warm WLED

Nowadays, Mn4+-activated fluoride red phosphors with high color purity, strong zero phonon line emission and relatively short decay time are crucial for improving the optical performance of WLED and emerging applications. In this work, a series of red-emitting Mn4+-activated fluoride phosphors in consideration of the non-equivalent substitution of Mn4+ for Ga3+ in the Na3GaF6 host are synthesized via the coprecipitation method at room temperature. The use of different reaction solvents successfully regulates the morphology, size and luminescence intensity of the phosphor. Under blue light excitation, Na3GaF6:Mn4+ sample shows a bright narrow-band red emission with exceptional correlated color temperature (4029 K). Moreover, the emission of strong zero phonon line induces the outstanding color purity of red light (93%). In addition, the critical concentration of Mn4+ is determined to be 0.04 and the concentration quenching mechanism is also systematically discussed. Noticeably, when Na3GaF6:Mn4+ phosphor achieves maximum fluorescence emission, its fluorescence lifetime value is only 3.48 ms. Additionally, the theoretical calculated results demonstrate that Na3GaF6 host can provide strong crystal field strength for Mn4+, and the Racah parameters (B and C) and nephelauxetic ratio (β1) are used to evaluate the nephelauxetic effect of Mn4+, which is compared with other types of Mn4+-activated phosphors. The activation energy, chromaticity shift and chromaticity coordinate variation are systematically calculated to analyze the thermal stability of Na3GaF6:Mn4+ red phosphor. Meanwhile, by employing the as-prepared phosphor Na3GaF6:Mn4+ as a red component, a high-performance warm WLED shows a full spectrum emission, and the corresponding cold white light emission is also transformed into the warm white light emission (CCT = 4224 K, Ra = 89.1 and LE = 111.72 lm/W). Moreover, under high driving current, such WLED exhibits stable output light efficiency. These results suggest that Na3GaF6:Mn4+ as red phosphor has a stupendous potential for warm WLED in indoor lighting.

Influence of the La2O3 addition on the structure and optical features of La2O3–NiO–BaO–B2O3 glass

The influence of the La2O3 addition on the microstructure, linear and nonlinear optical parameters of nickel borate glass was carefully investigated for the La2O3–NiO–BaO–B2O3 system. The La2O3 content of the present glass was varied from 0.0 to 10.0 mol%, while the glass modifiers of BaO and glass intermediate of NiO were fixed at 19 and 1.5 mol%, respectively. Based on the structural investigations, the bond density remarkably increased from 7.37 × 1019m−3 to 8.66 × 1019m−3 by a ratio of 18 % with increasing La2O3/B2O3 ratios. Additionally, the presence of Ni2+ ions as NiO6 units was confirmed by the brown shade originating from the absorption band observed at 427 nm in the optical absorbance of the studied glass. Furthermore, the Ni3+ ions do not play a role in the coloring of the glass. Moreover, the fundamental absorption edges of the glass shift towards lower energy values with increasing La2O3 concentrations, confirming the decreased behavior of the band gaps. Moreover, the linear and nonlinear refractive indices increase with increasing of La2O3 concentrations. Additionally, the ligand field characteristics of Ni cations, such as the ligand field splitting parameter and Racah parameter, exhibit opposite behaviors upon introducing additional La2O3 content. A decrease in values of the ligand field splitting, while the Racah parameters exhibit increased values. The observed outcomes demonstrate a tendency of the bonds connecting the Ni ions and their ligands to possess higher degrees of ionic nature. Based on the results, the present glass samples can function as solar thermal collectors by collecting sunlight and utilizing it for direct heating and indirect electrical power generation.

Synthesis, structural and optical properties of a novel double perovskite for LED applications

Amidst growing concerns for environmental sustainability and green ecology, the utilization of Light Emitting Diodes (LEDs) for indoor plant cultivation has emerged as an influential area of research. Nonetheless, the growth of indoor plants is often constrained by inadequate lighting. Consequently, designing novel LEDs to create an appropriate light environment has emerged as a focal point in research. As a new type of photocatalytic material with excellent optical properties and light stability, double perovskite has broad application prospects in LEDs manufacturing. In this context, this article aims to synthesize a new Ca2Lu(Nb,Mn)O6 double perovskite and study its optical properties in LEDs lighting for indoor plant growth. A new Ca2Lu(Nb,Mn)O6 double perovskite were synthesized using the traditional high-temperature solid-phase method. The crystal structure and luminescence properties of the double perovskite were characterized in detail using powder X-ray diffraction (XRD), Rietveld refinement, excitation and emission spectra, decay lifetimes, quantum efficiency (QE), electron paramagnetic resonance (EPR) spectra, temperature-dependent emission spectra, and the Commission International de l’Eclairage (CIE) color coordinates. The photoelectric properties of Ca2Lu(Nb,Mn)O6 and Ca2LuNbO6 double perovskite have been explored through first-principles investigations. The absorption spectra from 270 to 600 nm indicates that it can be effectively excited by ultraviolet (UV) light. The emission spectra show a strong broad red emission peak at 684 nm. The luminescence mechanism has been studied using the Tanabe-Sugano diagram. In addition, the internal UV emission ratio β1, crystal field strength Dq, and Racah parameters B and C were evaluated. The thermal stability of the sample was studied through emission spectra at heating temperatures from 303 to 573 K. The results indicate that Ca2Lu(Nb,Mn)O6 double perovskite provides a new solution for indoor plant growth.