Dipole Quadrupole Interaction Research Articles

A novel aluminum-oxynitride phosphor Mg0·695Si0·695Al1·39O3·65N0.35: Ce3+, Tb3+, Mn2+ based on cation substitution with double sites related multicolor-tunable luminescence

A new aluminum-oxynitride Ce3+-Tb3+ and Ce3+-Mn2+ co-doped Mg0·695Si0·695Al1·39O3·65N0.35 (MSAON) have been prepared by the high-temperature solid-state method at 1500 °C. The structure, photoluminescence properties, energy transfer (ET) mechanism, thermal quenching behaviors have been investigated. The MSAON host has been formed based on the co-substitution method of cation pair. Under UV excitation, the tunable-color emissions from violet to green and red can be realized by properly doping Ce3+/Tb3+/Mn2+ ions. In addition, the type of ET mechanism from Ce3+ to Tb3+ and Mn2+ both are confirmed to be electric dipole-quadrupole interaction. However, as temperature increases, the emission intensity of Tb3+ in MSAON: Ce3+, Tb3+ phosphor occurs a significantly rising trend until 493 K, which is caused by increasing energy transfer from Ce3+ to Tb3+ due to the effect of enhanced electron–phonon coupling with rising temperature. This property may be helpful for the investigation of ratiometric optical thermometry. Meanwhile, the MSAON: Ce3+, Mn2+ phosphor shows an excellent thermal stability, maintaining 84.25% of initial intensity at 423 K. The results suggest that they could be feasible multicolor-tunable emission phosphors for potential applications for near -UV WLEDs.

Charge compensation assisted enhanced photoluminescence derived from Al3+-codoped NaLaMgWO6:Mn4+ phosphors for plant growth lighting applications

A novel red-emitting phosphor NaLaMgWO6 (NLMWO):xMn4+ has been synthesized by a high-temperature solid-state reaction. The samples were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence excitation (PLE) and emission (PL) spectra. The results indicated that the phosphors could be efficiently excited by the near ultraviolet (NUV) and blue light. Due to the 2Eg → 4A2g transition of Mn4+ ion, the samples can exhibit red emission, which was consistent with the absorption spectrum required for plant growth. In addition, the concentration quenching mechanism was dipole-quadrupole (d-q) interaction of Mn4+ activator, when the optimal doping concentration of Mn4+ was determined to be 30 mol%. Moreover, the influence of Mn4+ and Al3+ ions co-doped on the PL properties of NLMWO were studied. The PL intensity of NLMWO:0.001Mn4+, 0.002Al3+ is 1.77 times than that of NLMWO:0.003Mn4+ phosphor. The results illustrated that the PL intensity of phosphors can be greatly improved via charge compensation. The obtained results validated that NLMWO:Mn4+ can be used as a new type of red luminescent powder absorbed by plant photosensitive pigment PFR to promote plant growth.

Photoluminescence properties and energy transfer of high thermal stable Na2GdPO4F2:RE (RE = Sm3+, Ce3+, Tb3+) phosphor for solid-state lighting

In this paper, a series of Na2GdPO4F2:Sm3+/Ce3+/Tb3+ phosphors had been synthesized via solid-state reactions and the luminescence properties of the phosphors had been investigated in detail. The Sm3+ ions in the host exhibited intense red emission under 402 nm irradiation and the mechanism for energy migration among Sm3+ ions was determined to be electronic dipole-dipole (d-d) interaction. For Ce3+ and Tb3+ codoped phosphors, the Ce3+→Tb3+ energy transfer took place, making the phosphor has intense green emission at 320 nm excitation. The mechanism for Ce3+→Tb3+ energy transfer had been verified as electronic dipole-quadrupole (d-q) interaction through the luminescence analysis using I–H model. The Na2GdPO4F2:Sm3+ and Na2GdPO4F2:Ce3+,Tb3+ phosphors both possessed pretty good thermal stability, and by coating them on the UV chips, red and green LED devices had been obtained, respectively. Moreover, utilizing the Tb3+ ions as bridges, Ce3+→Tb3+→Sm3+ energy transfer had been observed in NGPF:Ce3+,Tb3+,Sm3+ phosphor. The investigation results on the property of as-prepared samples indicated that Na2GdPO4F2 is a good host for rare earth ion doping and the Na2GdPO4F2:Sm3+ and Na2GdPO4F2:Ce3+,Tb3+ might be potential UV excited red and green phosphors for UV-WLEDs.

Warm white emission of LaSr2F7:Dy3+/Eu3+ NPs with excellent thermal stability for indoor illumination

The novel single Dy3+-activated and Dy3+/Eu3+ co-activated LaSr2F7 NPs-based phosphors were successfully synthesized via a simple precipitation reaction method at room temperature. The phase formations and cell parameters of single Dy3+-activated and Dy3+/Eu3+ co-activated LaSr2F7 NPs were verified in detail by the Rietveld refinement technique based on the recorded X-ray diffraction patterns. The doping concentration of single Dy3+-activated LaSr2F7 NPs was optimized to be 0.1 mol with the concentration quenching dominated by the electric dipole-dipole interaction. Meanwhile, a variety of Eu3+-activated La0.9Sr2F7:0.1Dy3+ NPs exhibited tunable luminescent properties and emitted warm white light in close to standard warm white light under 363 nm excitation. The valid energy transfer (ET) efficiency from Dy3+ to Eu3+ ions was estimated to be about 86.02% based on the emission intensity while the electric dipole-quadrupole interaction dominated the concentration quenching mechanism in ET process. Eventually, the thermal quenching of the obtained samples was studied, showing the excellent thermal stability. All the results manifest that Eu3+-activated LaSr2F7:Dy3+ NPs could emit warm white light with excellent thermal stability for indoor illumination.

A new potential green-emitting erbium-activated α-Na3Y(VO4)2 nanocrystals for UV-excitable single-phase pc-WLED applications

A potential UV-excitable green-emitting erbium-doped α-Na3Y(VO4)2 nanocrystalline phosphor has been successfully synthesized via facile citrate-based solution combustion method. The structural characterization of the sample was carried out using X-ray diffraction, TEM, HRTEM, SAED, EDS and FTIR analysis. The phosphor exhibits green emission at 523 nm and 552 nm, which correspond to 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+, respectively. The energy transfer mechanism among Er3+ ions and the concentration mechanism have been studied. The optimal doping concentration of Er3+ in the α-Na3Y(VO4)2 is found to be 0.025 mol. The non-radiative interaction among Er3+ is attributed to the dipole–quadrupole interaction. The quantum yield is found to be 7.25%, and chromaticity coordinates for the optimal concentration are found to be (0.2571, 0.6707) which are close to National Television System Committee standards for green (0.21, 0.71). The lifetime of erbium emission is found to be in microsecond range. The photoluminescence studies reveal that the newly synthesized Er3+-doped α-Na3Y(VO4)2 nanocrystals would be a good choice as green emitter to be combined with previously investigated blue- and red-emitting Tm3+- and Sm3+-doped α-Na3Y(VO4)2 nanocrystals for realizing RGB phosphor.

Investigations on energy transfer mechanism and tunable luminescent properties of Co-doped Ca9La(PO4)7:Dy3+,Eu3+ phosphors

The synthesized Ca9La(PO4)7:Dy3+,Eu3+(CLPO:Dy3+,Eu3+) phosphors were analyzed by phase structure, optical performance, thermal stability and lifetime. The XRD pattern indicated that both the matrix and rare earth ion-doped phosphors were pure phases, and the crystal structure was confirmed as trigonal system. Upon 351 nm excitation, Dy3+-doped CLPO phosphors performed two strong emission peaks at 481 nm and 573 nm. The energy transfer phenomenon from Dy3+ to Eu3+ can be found in the Dy3+, Eu3+ co-doped CLPO phosphors, and the color was tuned from red to blue upon 395 nm excitation with Eu3+ concentration decreasing. The energy transfer characteristic was evidenced by the excitation spectra, emission spectrum and decay time of the synthesized phosphors, and the mechanism of energy transfer from Dy3+ to Eu3+ was evaluated as a dipole–quadrupole interaction. In addition, temperature-dependent spectra were performed and the activation energy was further evaluated about 0.1902 eV. The results indicate the potential application of CLPO:Dy3+,Eu3+ phosphors in white LEDs.

Egg albumin assisted sol-gel synthesis of Eu3+ doped SnO2 phosphor for temperature sensing

SnO2: Eu3+ phosphors were prepared via egg albumin assisted sol-gel method. The typical sample SnO2: Eu3+ had tetragonal rutile structure. The sample SnO2: Eu3+ had irregular lamellar structure and serious agglomeration. The optical bandgap values of samples were in the range of ∼3.92–4.36 eV. When Eu3+ concentration was 2.0 %, concentration quenching of dipole-quadrupole (d-q) interaction type occurred. Based on the non-thermally coupled energy level fluorescence intensity ratio, the sample SnO2: 2%Eu3+ had the maximum absolute sensitivity of ∼0.87565 K−1 at 373 K. The relative sensitivity was estimated to be 2854.42/T2 K−1, and the maximum relative sensitivity was 3.214 % K−1 at 298 K, which had great potential application in the field of temperature sensing.

Extension of Cubic-Plus-Polar (CPP) equation of state (EoS) for application in aqueous electrolyte solutions

In this study, an extension of Cubic-Plus-Polar (CPP) equation of state (EoS), i.e. electrolyte CPP (eCPP), was proposed to study various aqueous binary electrolyte solutions as well as water-CO2-NaCl, water-CO2-Na2SO4, and water-H2S-NaCl ternary systems. To avoid complexity, polar (dipole-dipole, quadrupole-quadrupole, and dipole-quadrupole) interactions were only considered for water, CO2, and H2S components, not for the studied ionic species in electrolyte solutions. In this work, the long-range electrostatic contribution was taken into account by Pitzer-Debye-Huckel equation. The proposed model has three adjustable parameters for each electrolyte, which were determined by fitting to experimental mean activity coefficient and liquid molar volume data of 79 aqueous strong electrolyte solutions at 0.1 MPa and 298.15 K. The overall average absolute relative deviation (AARD) between model-calculated values and experimental data were 1.05% and 1.44% for liquid molar volume and mean activity coefficient, respectively, while this value was 1.27% for predicted results of osmotic coefficient. Moreover, eCPP EoS predicted the liquid molar volumes of 15 different electrolyte solutions with an overall AARD of 0.6% in a wide range of pressure, temperature, and electrolyte concentration. The reliability of the proposed EoS (eCPP) was verified by the obtained AARDs.

Structural and optical investigation of Tb3+-doped Ba3Y4O9 nanocrystals for solid state lighting applications

Ba3Y4O9:Tb3+ (0.5–3 ​mol%) nanophosphors were prepared by adopting urea-assisted solution combustion route. Phase purity and crystal structure were identified from XRD based Rietveld refinement technique. Morphologies and dimensions of combustion-derived particles were examined on scanning and transmission electron microscopes (SEM & TEM). To calculate band-gap energies for Ba3Y4O9 (5.31 ​eV) and Ba3Y3.92Tb0.08O9 nanophosphors (5.20 ​eV), diffuse reflectance (DR) measurements were carried out. The effect of Tb3+ concentration on down-converted photoluminescence (PL) properties were studied. Upon UV-excitation (292 ​nm), the emission spectra exhibited most intense green band at 544 ​nm derived from allowed 5D4 → 7F5 transition. The energy transfer mechanism was explained in terms of dipole-quadrupole interactions (s ​= ​7.87), for which Rc was evaluated as 18.64 ​Å. Radiative lifetime, non-radiative rates, quantum efficiencies and Commission International de I’Eclairage (CIE) coordinates were also calculated. Results finally illustrate that Ba3Y4O9:Tb3+ green-emitters might be the potential candidature in UV-pumped white LEDs.

Tunable blue–green–emitting Na4CaSi3O9:Ce3+,Li+,Tb3+ phosphor with energy transfer for near-UV white LEDs

Phosphor-converted white light emitting diodes (w-LEDs), with high luminous efficiency, low energy consumption, extended lifetime, and eco-friendly nature, have revolutionized various industries. Among them, an alkaline earth silicate-based phosphor host, Na4CaSi3O9, shows good crystal structure stability and flexible properties for diverse application. Here, Ce3+/Li+ singly doped and Ce3+/Li+/Tb3+ co-doped Na4CaSi3O9 phosphors are fabricated by the standard solid-state reaction approach. The Ce3+/Li+-activated phosphors show strong absorption within 200–400 nm and exhibit a blue emission centered at 423 nm. The quenching concentration of Ce3+ appears at x = 0.05 and can be attributed to the dipole–quadrupole interaction. When Tb3+ ions are co-doped, the Na4CaSi3O9:Ce3+,Li+,Tb3+ phosphor emission can be adjusted from blue to green under the irradiation of 365 nm through the dipole–dipole interaction induced energy transfer from Ce3+ to Tb3+ ions with a maximum value of 28.32%. This study highlights the Na4CaSi3O9:Ce3+,Li+,Tb3+ phosphors as a new and efficient material for w-LED applications.

Insight into energy transfer, color tuning, and white emission in Tm3+ and Dy3+ codoped Ca8ZnLa(PO4)7 phosphors

A series of Ca8ZnLa(PO4)7: 0.01 Tm3+, xDy3+ (x = 0–0.15) and Ca8ZnLa(PO4)7: 0.1Dy3+ phosphors were obtained via the high temperature solid state reaction method. The crystal structure, photoluminescence properties, and energy transfer from Tm3+ to Dy3+ were investigated. The prepared phosphors possess the β-Ca3(PO4)2 structure and belong to the R3c (161) space group. The luminescent colors of Ca8ZnLa(PO4)7: 0.01 Tm3+, xDy3+ phosphors can be modulated from blue to yellow and white light emission of a single matrix was realized. In the Ca8ZnLa(PO4)7 (abbreviated as: CZLPO) matrix, the Tm3+→Dy3+ energy transfer process proceeds due to electric dipole-quadrupole interaction, and the energy transfer mechanism is explored in detail according to Dexter's energy transfer theory and Reisfeld's equation. Moreover, the CZLPO: 0.01 Tm3+, xDy3+ phosphors exhibit good thermal stability. These characteristics indicate that a single matrix CZLPO: 0.01 Tm3+, xDy3+ phosphor has a potential for applications in white LEDs.

Effects of Ti4+- and W6+-substitution on photoluminescence properties of Sr2GdSbO6:Mn4+ phosphor for plant cultivation

A novel double perovskite Ti4+ and W6+ modified Sr2GdSbO6 (SGSO):Mn4+ far-red phosphor was prepared by traditional solid state reaction method. The samples were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence spectra (PL), decay life, temperature-dependent emission spectra and internal quantum efficiency (IQE). Due to the 2E→4A2 transition of Mn4+ ions, the emission band centered at 667 nm was observed in the range of 600–780 nm, which matched the absorption spectra required for plant growth. The excitation spectra consist of four excitation bands, peaking at 276, 305, 358 and 506 nm in the range of 220–600 nm, respectively, which indicates that SGSO:Mn4+ phosphors can be excited by ultraviolet, near-ultraviolet and blue light emitting diode (LED) chips. The optimum doping concentration of Mn4+ is determined to 0.4 mol% and the concentration quenching mechanism is the dipole-quadrupole interaction of Mn4+ activator. The effect of co-doping Ti4+ and W6+ ions on the luminescent properties of SGSO:Mn4+ was studied. The PL intensity of SGSO:0.004Mn4+, 0.004Ti4+ and SGSO:0.004Mn4+, 0.004 W6+ are 1.65 and 2.07 times than that of SGSO:0.004Mn4+ phosphor. Impressively, all samples possess excellent thermal stability (I423K/I298K>70%). The results illustrate that Ti4+ and W6+ can significantly improve the luminescent properties and thermal stability of SGSO:Mn4+. Finally, a kind of LED device was fabricated by combining 365 nm ultraviolet LED chip with far-red light emitting SGSO:0.004Mn4+, 0.004 W6+ phosphors and BaMgAl10O17:Eu2+ blue phosphor. Because the emission band of SGSO:0.004Mn4+, 0.004 W6+ matches well with the absorption band of plant pigment PR, under the excitation of near ultraviolet (UV) to blue light, SGSO:0.004Mn4+, 0.004 W6+ phosphors have potential application prospects in indoor plant cultivation.

New full color emitting phosphor through energy transfer in Bi3+ and Eu3+ co-doped La3TaO7 weberite system

A new full color emitting single phase phosphor in Bi3+ and Eu3+ ion co-doped La3TaO7 weberite system was developed via a conventional high temperature ceramic method. Phase, structural and luminescence characteristics of the developed phosphor were evaluated with different concentrations of Bi3+ and Eu3+ ions. The structural studies show that the samples are crystallized into orthorhombic weberite type structure with Cmcm space group. Photoluminescence studies reveal that the Bi3+ and Eu3+ ions co-doped La3TaO7 phosphors show broad excitations in the n-UV region (270 nm, 336 nm, 394 nm), and displays broad bluish-green emission due to the 1S0 to 3P1 and 1P1 transitions of Bi3+ and intense orange-red emission due to 5D0 to 7F0-2 transitions of Eu3+ leading to cover the whole visible spectral region. The lifetime measurements and the overlap of the spectral regions with the variation of Eu3+ concentration with Bi3+ suggest an effective energy transfer from Bi3+ to Eu3+, allowing to fine tune the chromaticity coordinates close to the white point. Further, the energy transfer mechanism existing in this phosphor is established, and it is found to be due to the dipole–quadrupole interaction. These properties make it an irrefutable candidate for single phase phosphor material for WLED application.

Realizing bright blue-red color-tunable emissions from Gd2GeO5:Bi3+,Eu3+ phosphors through energy transfer toward light-emitting diodes

Novel Bi3+/Eu3+ ions co-doped Gd2GeO5 (GGO) phosphors were prepared by a high-temperature solid-state reaction method. X-ray diffraction, photoluminescence (PL), CIE chromaticity coordinates, internal quantum efficiency (IQE), and temperature-dependent PL spectra were applied to analyze the as-obtained phosphors. The emission spectra of the GGO:Bi3+,Eu3+ phosphors showed both a broad blue band of Bi3+ emission centered at 453 nm and the characteristic sharp red emission lines of Eu3+, corresponding to the 3P1→1S0 allowed transition of the Bi3+ ions and the 5D0→7FJ (J = 0, 1, 2, 3, 4) transitions of the Eu3+ ions, respectively. Notably, the as-prepared GGO:Bi3+,Eu3+ phosphors exhibited color-tunable emissions from blue (Bi3+) to red (Eu3+) with increasing the Eu3+ doping concentration via a high-efficiency energy transfer process. Moreover, the mechanism of energy transfer from Bi3+ to Eu3+ ions was determined to be the dipole-quadrupole interaction. Impressively, the optimal GGO:0.05Bi3+,0.12Eu3+ phosphors had an outstanding IQE as great as 88% and good thermal stability. All these meaningful results demonstrated that blue-red color-tunable GGO:Bi3+,Eu3+ phosphors have potential applications in white light-emitting diodes (LEDs) and plant growth LEDs.

Photoluminescent properties of single-phase white-light Ca8ZnGd(PO4)7:Eu2+,Mn2+ phosphor

The Eu2+ activated Ca8ZnGd(PO4)7:Eu2+ green light emitting phosphors and Eu2+/Mn2+ co-doped tunable light emitting phosphors Ca8ZnGd(PO4)7:Eu2+,Mn2+ were successfully synthesized via the solid-state reaction method. The X-ray powder diffraction measurements and Rietveld refinement were used to assess the phase composite and crystal structure. The photoluminescence properties, diffuse reflection spectrum, chromaticity coordinates and fluorescence decay curves of the samples were investigated. It has been confirmed that the resonant type Eu2+→Mn2+ energy transfer occurs via a dipole-quadrupole interaction. With various Eu2+/Mn2+ molar ratios, the spectrum-tunable phosphors are obtained from green (0.183, 0.335) to white (0.297, 0.298).

Sr2LaSbO6:Mn4+ far-red phosphor for plant cultivation: Synthesis, luminescence properties and emission enhancement by Al3+ ions

A series of novel Mn4+-activated double perovskite antimonate Sr2LaSbO6 (SLSO) far-red emitting phosphors were successfully synthesized by a high-temperature solid-state method. X-ray diffraction (XRD), photoluminescence excitation (PLE) and emission (PL) spectra, temperature-dependent photoluminescence spectra, CIE chromaticity coordinates, as well as internal quantum efficiency (IQE) were used to analyze these phosphor samples. Under 334 nm excitation, the SLSO:Mn4+ phosphors emit far red emission peaking around 694 nm due to the Mn4+: 2Eg→4A2g transition. The optimal doping concentration of Mn4+ was 0.8 mol%, moreover, the critical distance (Rc) was 40.89 Å. The dipole-quadrupole interaction may be responsible for the concentration quenching mechanism of Mn4+ ions in the SLSO:Mn4+ phosphors. Furthermore, various Al3+ improved SLSO:0.008Mn4+ phosphors are investigated. When Al3+ is doped with 0.8%, the PL intensity increased by 2.92 times. In addition, the IQE of SLSO:0.008Mn4+ and SLSO:0.008Mn4+, 0.008Al3+ were found to be as high as 35.2% and 38.1%, respectively. Impressively, all chromaticity coordinates of samples located in far-red region. Therefore, these superior luminescence properties of SLSO:Mn4+ sample demonstrated its potential applications in plant cultivation and growth light-emitting diodes (LEDs).

Structure, energy transfer, and luminescence properties of NaLaMgWO6: Tb3+,Eu3+ phosphors for solid-state lighting

Novel NaLaMgWO6:Tb3+,Eu3+ phosphors with tunable color emissions were prepared by a solid-state reaction. The crystal structure, composition, and luminescent properties of the obtained phosphors were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and fluorescence spectrophotometer. The results reveal that NaLaMgWO6 crystallizes in a monoclinic double perovskite structure with C2/m space group. Tb3+ and Eu3+ single-doped phosphors show the intense green and red emissions at 545 and 617 nm, corresponding to the 5D4 → 7F5 transition of Tb3+ and the 5D0 → 7F2 transition of Eu3+, respectively, while for Tb3+ and Eu3+ co-doped phosphors, a tunable emission color from green to red is obtained by variation of the ratio of Eu3+ to Tb3+. The emission spectra and luminescence decay lifetimes verify the occurrence of energy transfer from Tb3+ to Eu3+ in NaLaMgWO6: Tb3+, Eu3+ phosphor, and the energy transfer mechanism is dominated by the dipole–quadrupole interaction. Furthermore, the thermal stability of NaLaMgWO6:Tb3+, Eu3+ phosphor was discussed from 305 to 515 K. The results exhibit the phosphors possess excellent thermal stability, and the activation energy is calculated to be 0.302 eV.

Abnormal field-dependence of magnetocaloric effect in ErB4 and TmB4

The coupled system of multi-degrees of freedom, such as charge, spin, orbital and lattice, has recently received much attention due to its potential to improve the magnetocaloric effect (MCE). The exotic inverse MCE was observed in rare-earth tetraborides of Ho1-xDyxB4 (x = 0.0, 0.5, and 1.0), associated with a strong coupling between magnetic dipoles and orbital quadrupoles in the strong spin-orbit coupling and geometric frustration. Here, the magnetism and magnetocaloric effects of ErB4 and TmB4 are investigated. It shows the maximum entropy changes of 11.4 J/kgK, and 12.6 J/kgK with the field of ΔH ≈ 40 kOe (H∥c) in ErB4 and TmB4, respectively. The field- and temperature-dependence of the entropy change is found to be quite different from those of the conventional MCE. And the entropy change is also found to have strong correlation with the field induced meta-magnetic transition. Because the field induced transition is due to magnetic moment reorientation, which is strongly coupled with quadrupole moment, the abnormal MCE of ErB4 and TmB4 is attributed to the dipole-quadrupole interaction and magnetic frustration. Thus, it supports the fact that the strong coupling between quadrupole and magnetic dipole moments plays important role in the exotic inverse MCE in rare-earth tetraboride system.

Achieving white-light/tunable emissions via the controllable energy transfer in the single Ba9La2Si6O24:Eu3+,Bi3+ phosphor for UV converted white LEDs

Nowadays, ultraviolet (UV) and blue converted phosphors have played a key role in the solid-state lighting field, and the white light is usually produced by mixing multiple phosphors. In this work, we report a type of UV converted single white phosphor, i.e., Ba9La2Si6O24:Eu3+,Bi3+.Various techniques, such as powder X-ray diffraction (XRD), scanning electron microscopic (SEM), photoluminescence (PL) spectra, and quantum efficiency (QE), have been used to characterize the samples. In Bi3+ doped samples, upon excitation within the wavelength range of 250–380 nm can lead to three Bi3+ emission bands (i.e., 358 nm, 415 nm, and 516 nm), but only one emission band peaking at 415 nm appears when the excitation wavelength exceeds 380 nm. Structural analysis and discussion on the PL intensity variation reveal there are three Bi3+ luminescent centers at two different La3+ sites and one Ba2+ site. The Bi3+ concentration-induced luminescent quenching is dominated by the d-d interaction. In view of the spectral overlap between the Bi3+ emissions and the Eu3+ excitation spectra, the energy transfer from Bi3+ to Eu3+ of the Ba9La2Si6O24:Eu3+,Bi3+ is studied, and it is dominated by a dipole-quadrupole (d-q) interaction. Moreover, upon excitation at 365 nm, the emissions broadly tuning from blue, white and to red are achieved by varying the Eu3+ content. For the white Ba9La2Si6O24:Eu3+,Bi3+ sample, high temperature PL results show that it does not have severe degradation of emission intensity after increasing the temperature from 25 to 300 °C, exhibiting a good thermal stability. To show the potential application in the lighting fields, we fabricate a white light LEDs device by depositing this white phosphor on a 365 nm UV LED chip. As a result, the values, i.e., a color rendering index (CRI) of 95, luminous efficiency of 80 lm/W, and color temperature (CT) of ~4215 K at chromaticity (0.382, 0.398), are achieved.

Crystal configuration and photoluminescent aspects of red-emitting combustion synthesized novel BaYZn3AlO7: Eu3+ nanophosphor

A facile and less time-consuming technique, namely, solution combustion synthesis (SCS) was employed for generating a series of novel BaY1-xZn3AlO7: xEu3+ (x = 0.05–0.30) nanophosphor. Powder X-ray diffraction (PXRD) patterns supported with Rietveld refinement technique validated the subsistence of a pure hexagonal BaYZn3AlO7 phase belonging to P63mc (186) space group. Both Scherrer’s equation as well as transmission electron microscope (TEM) study, were in strong agreement in terms of nano-size of the synthesized phosphor. The obtained nanostructures display a most prominent peak in their emission spectra at 611 nm owing to 5D0→7F2 transition resulting in red-emission upon excitation by a source of near-ultraviolet (NUV) light (λex = 393 nm). The observed CIE coordinates for this strong emission in an optimized nanophosphor (BaY0.80Eu0.20Zn3AlO7) were 0.592, 0.407. Judd-Ofelt parameter (Ω2) is evaluated for all compositions of combustion derived nanosamples utilizing their recorded emission spectra by applying Judd-Ofelt theory. The standard host and synthesized nanophosphor containing optimum concentration of Eu3+ i.e. BaY0.80Eu0.20Zn3AlO7 were examined via diffuse reflectance spectroscopy (DRS) and the evaluated energy band gap were established to be 4.67 eV and 4.61 eV respectively. In addition, dipole-quadrupole interactions were apt to cause the observed concentration quenching (CQ) trend as the value of critical distance evaluated as 11.88 Å. Correlated color temperature (CCT) value for the optimized novel nanophosphor was ∼1714 K confirming their applications in the warm light-emitting diodes (LEDs).