Phosphors For Solid State Lighting Applications Research Articles

Structural, optical, and thermal traits of Sm³⁺-doped SrB₂O₄ phosphors for solid-state lighting applications

We synthesized Sm³⁺-doped SrB₂O₄ phosphors through a solid-state reaction method, varying the Sm³⁺ doping concentrations. Structural and morphological characteristics of material were investigated using Fourier-transform infrared spectroscopy (FTIR), X-Ray Diffraction (XRD) and scanning electron microscopy (SEM). Optical transitions were analyzed by recording the diffuse reflectance spectroscopy, while photoluminescent (PL) spectra were used to evaluate luminescence properties. The PL spectra revealed a strong orange emission at 598 nm under 402 nm excitation. The optimal Sm³⁺ doping concentration was determined to be 0.02 mol, beyond which concentration quenching occurred. This quenching is attributed to exchange-type interactions, which facilitate non-radiative energy relaxation. The CIE color chromaticity coordinates of all the synthesized phosphors fell within the orange region of the chromaticity diagram. Temperature dependent photoluminescence revealed lower activation energy and phonon energy. Thermal quenching temperature was calculated which is inline with commercially available LEDs. All of these results indicate the candidature of SrB2O4 phosphor doped with Sm3+ ions for solid state lighting and optical thermal sensing applications.

Comparative investigation of structural, morphological and temperature-dependent photoluminescence characteristics of trivalent rare-earth-activated NaCaPO4 phosphors for solid-state lighting applications

This study explores the synthesis, structure, morphology, and photoluminescence features of trivalent RE3+-activated NaCaPO4 phosphors, aiming to develop phosphor materials for white-light-emitting diode (WLED) applications. Single-phase polycrystalline NaCa(1-x) REx3+ PO4 (REx3+ = Sm, Eu, Dy, and Tb) phosphor materials with various REx3+-doping percentiles were produced by a solid-state reaction process, which were analyzed using various characterization techniques. The FullProf Suite software program was used for phase evidence and crystalline structure analysis, confirming the composition of orthorhombic materials as a single phase. FE-SEM micrographs revealed asymmetrically stacked morphologies across all the compositions. This study reveals that trivalent RE3+-activated phosphors produced exceptional PL outcomes. Dexter's and Blasse's approaches were used to establish the interaction mechanisms and critical energy transfer ranges as dipole-dipole. Lifetime decay patterns were used to fit a bi-exponential function and the resulting values were approximated in milliseconds. This study reveals that trivalent RE3+-activated NaCaPO4 phosphors, with their thermal resilience and color integrity, have potential applications in solid-state lighting (SSL) technology.

Synergistic effects of zinc thiocyanate on the performance of cesium lead bromide perovskite phosphors for solid-state lighting applications

All inorganic lead halide perovskites have led to a new paradigm shift in display and lighting technologies because of significant cost and performance advantage over the current state-of-the-art optoelectronics. However, the applications of these perovskites are undermined due to the toxicity and severe degradation of the materials in response to external stimuli. This research highlights the synergetic effects of co-doping of CsPbBr3 nanocrystals (NCs) at its B- and X-site using zinc thiocyanate (Zn(SCN)2). The adopted doping strategy helps to improve the photoluminescence stability of the pristine NCs when stored under ambient conditions for 156 days. This is attributed to the enhanced local structural order and reduced inhomogeneous strain between the lattices of the NCs due to the synchronized effect of Zn2+ and SCN–. The composite NCs are integrated as color-converting layers (thin 3D printing layer coated with NCs) with a blue LED chip to obtain the white light. It exhibits bright white emissions with a color rendering index of 86, correlated color temperature of 6046 K, and color coordinates close to standard white light. This work emphasizes the strong potential of inexpensive and earth-abundant Zn(SCN)2-based CsPbBr3 composites to meet consumer needs.

Judd-Ofelt analysis of Sm3+ doped Ca2LiMg2V3O12 phosphors: Unveiling luminescent and thermometric properties for multifunctional applications

This study investigated the luminescent and thermometric properties of pure and Sm³⁺-doped Ca₂LiMg₂V₃O₁₂ (CLMV) garnet-type vanadates synthesized by the solid-state reaction method. The synthesized materials, with varying Sm³⁺ concentrations (0.01–0.09 mol%), were comprehensively characterized using powder X-ray diffraction (PXRD) analysis to confirm their phase purity. Diffuse reflectance spectroscopy (DRS) measurements were employed to determine the band gap energy of both pure CLMV and CLMV:0.07Sm³⁺ samples. Photoluminescence (PL) excitation and emission spectra were recorded for the pure and Sm³⁺-doped CLMV phosphors using an excitation wavelength of 345 nm and monitoring the emission at 618 nm. These spectra revealed detailed information about the energy levels involved in light emission processes. An efficient energy transfer from the (VO₄)³⁻ groups to the Sm³⁺ ions was observed, exceeding 48%. This energy transfer process is crucial for achieving high-intensity luminescence in Sm³⁺-doped materials. Judd–Ofelt (J-O) theory was applied from the emission spectra and calculate the Judd–Ofelt intensity parameters, which govern the radiative properties of the Sm³⁺ ions. Based on the J-O analysis, the branching ratio (β) was estimated to be greater than 75%. This value, exceeding the threshold of 50% for display devices, signifies the suitability of the phosphor for solid-state lighting applications due to its efficient light emission. The thermal quenching behavior of both the Sm³⁺ ions and the (VO₄)³⁻ groups was further investigated to explore the optical thermometric characteristics of the Sm³⁺-doped CLMV phosphors. Notably, a maximum absolute sensitivity (Sa) of 0.35 K⁻1 and a relative sensitivity (Sr) of 2.55% K⁻1 were achieved, demonstrating the materials potential for non-contact optical temperature sensing applications. Lifetime decay analysis revealed double exponential decay behavior, indicating the presence of multiple luminescence centers within the phosphor. The average lifetime in the millisecond range further supports the suitability of these materials for practical applications. Finally, the CIE color coordinates, correlated color temperature (CCT), and color rendering index (CRI) values were also reported, providing insights into the colorimetric properties of the Sm³⁺-doped CLMV phosphors. These aspects are crucial for optimizing the materials for solid-state lighting applications.

Spectroscopic investigation by incorporation of charge compensator ions in CaBaSiO4: Dy3+ phosphors for solid-state lighting applications

Spectroscopic investigation by incorporation of charge compensator ions in CaBaSiO4: Dy3+ phosphors for solid-state lighting applications

Synthesis and characterization of thermally stable red light-emitting Eu3+ activated Li7La3Zr2O12 phosphors for solid-state lighting applications

To enhance the photoluminescence property of Li7La3Zr2O12 (LLZO), Eu was doped using a solid-state synthesis technique. X-ray diffraction and Raman spectroscopy analysis were used to examine the crystal structure of the synthesized phosphors. The optical band gap values of pristine and Eu3+ doped LLZO phosphor investigated using ultraviolet-visible (UV-Vis) spectroscopy were measured to be 2.74 and 2.97 eV, respectively. The wavelengths of pure and doped LLZO samples were measured and fitted by the Commission Internationale de l’Eclairage (CIE) chromatic coordinate graph. These samples were found to emit blue emission at 354 nm (pure LLZO) and red emission at 464 nm (doped phosphor), which correspond to the 5D0 to 7Fj (j = 0, 1, 2, and 3) transition. The purity of the color and correlated color temperature with respect to the 0.9 M.W% Eu3+ doped (activated) LLZO sample were estimated to be 80% and 1719K, respectively. The indication of its maximum emissive capability at this rate was found suitable for aesthetic lighting applications.

Luminescence properties of ZrO2: Dy3+ phosphor for solid-state lighting applications

Herein, we report Dy3+-activated ZrO2 phosphors synthesized via the sol-gel technique. The structural, morphological, and optical properties of the synthesized powder samples annealed at 900 °C were investigated. The monoclinic phase of the synthesized phosphor was confirmed by recording the X-ray powder diffraction (XRPD) pattern. Ultraviolet–visible analysis was performed for the reflectance and bandgap measurements of the phosphors. Field emission scanning electron microscope and X-ray energy dispersive spectroscopy analyses were used to study the morphology and elemental composition of the phosphors, respectively. The distribution of ions in the undoped and Dy3+-doped samples was confirmed using time-of-flight secondary ion mass spectroscopy. The photoluminescence (PL) behavior of the synthesized phosphors was investigated by recording the excitation and emission spectra. When the synthesized phosphors were exposed to UV light at 353 nm, we observed characteristic blue and yellow Dy3+ PL emissions, corresponding to the transition 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2, respectively. Additionally, we observed low-intensity red and brown-red emission peaks corresponding to 4F9/2 → 6H11/2 and 4F9/2 → 6H9/2. These observations indicate that the non-aqueous sol-gel route, coupled with the suitable post-synthesis heat treatment, resulted in the development of a monophase (monoclinic) zirconia. This makes it a strong candidate for phosphor applications due to its high room temperature stability and efficient characteristic features of the monoclinic phase. These findings strongly suggest that Dy3+-doped ZrO2 can serve as a superior phosphor material for white light-emitting diode applications.

Photoluminescence features of trivalent holmium doped Ca2La8(SiO4)6O2 phosphors

Abstract This study examines the optical properties of Ca2La8−x (SiO4)6O2:xHo3+ phosphors derived using the sol–gel method. X-ray diffraction data and Rietveld analysis confirmed that the phosphors formed in hexagonal phase with an average estimated crystalline size of 27 nm. The prominent excitation peak observed at wavelength 463 nm corresponding to excitation energy 2.68 eV was due to the 5I8 → 5G6 + 5F1 transition. The photoluminescence emission spectra revealed that the synthesized phosphors emitted in the green color region with the 5S2 + 5F4 → 5I8 transition, releasing 2.27 eV energy. The emission and excitation analyses revealed the presence of concentration quenching as the Ho3+ concentration exceeded 0.03 mol in the Ca2La8−x (SiO4)6O2:xHo3+ series. Further, photometry analysis demonstrated a color purity exceeding 94 %, which supports the candidacy of these phosphors for solid-state lighting applications.

Comparative photoluminescence study of MAlB3O7:Dy3+ (M=Ca, Sr) phosphor for solid-state lighting applications

Comparative photoluminescence study of MAlB3O7:Dy3+ (M=Ca, Sr) phosphor for solid-state lighting applications

Synthesis, photoluminescence, Judd-Ofelt analysis, and thermal stability studies of Dy3+-doped BaLa2ZnO5 phosphors for solid-state lighting applications.

Here, we report a series of white-emitting Ba(La2-x Dy x )ZnO5 (x = 0-7 mol%) phosphors synthesized via a high-temperature solid-state reaction. The synthesized phosphor's phase purity and tetragonal crystal structure were confirmed by an X-ray powder diffraction (XRPD) pattern. The wide bandgap characteristic feature was assessed through reflectance spectra, and the estimated bandgap was found to be 4.70 eV. Besides analyzing the effect of doping on the surface morphology, the distribution of ions on the surface was observed through the secondary ion mass spectroscopy technique. The synthesized phosphor was found to display bluish (486 nm) and yellowish (576 nm) bands in the emission spectra under the excitation of 325 nm and 352 nm, which together are responsible for producing the white luminescence. The analysis of Judd-Ofelt parameters indicates the symmetric nature of Dy3+ substitution in the present host. The thermal stability of the phosphor was assessed by varying the temperature up to 403 K, and it was found that the synthesized phosphor possesses improved thermal stability with an activation energy of 0.29 eV. The photometric evaluations of the present phosphor revealed the CIE coordinates around the near-white regime (0.3448, 0.3836), along with the color-correlated temperature value of 5102 K. All research on this luminescent material's unique features points to the possibility of using it to fabricate white-light-emitting devices for solid-state lighting applications.

Corrugated 1D Hybrid Metal Halide [C6H7ClN]CdCl3 Exhibiting Broadband White-Light Emission.

Organic-inorganic hybrid metal halides (OIMHs) exhibiting white-light emission are a splendid class of emitters and are regarded as desired phosphors for solid-state lighting applications. Here we report a single-component white-light-emitting hybrid metal halide, namely, [C6H7ClN]CdCl3 (C6H7ClN = 4-(chloromethyl)pyridinium), which features a corrugated 1D anionic double chain composed of edge-shared CdCl6 octahedrons and exhibits broadband white-light emission with a photoluminescence quantum yield of 12.3% under 365 nm UV light irradiation. Density functional theory calculations and temperature-dependent emission spectral analysis unveil that the broadband emission of [C6H7ClN]CdCl3 is ascribed to self-trapped excitons. Moreover, a single-component white-light-emitting diode device with a correlated color temperature of 5214 K and color rendering index of 83.7 can be fabricated via coating [C6H7ClN]CdCl3 on a 365 nm UV light-emitting diode chip. Such a promising luminescent material provides guidance for the design and synthesis of OIMHs with unique structures and desired properties.

Near-UV excited green-emission enhancement by efficient energy transfer in Na1.8Mg0.9Si1.1O4:Ce3+,Tb3+ phosphor for solid-state lighting applications

Luminescence properties of phosphor play a key role in the performance of white light-emitting-diodes (LEDs). The Tb3+ emission under near-UV excitation is usually very weak due to f-f spin-forbidden transitions. In this paper, we report that Tb3+ emission under near-UV excitation enhances up successfully in Ce3+,Tb3+ co-doped Na1.8Mg0.9Si1.1O4 (NMSO) phosphor, as a result of efficient energy transfer from Ce3+ to Tb3+. The newly-prepared NMSO:Ce3+,Tb3+ exhibits a strong green-emission line at λmax = 545 nm under 340 nm excitation, and the quantum efficiency is 0.82. The maximum energy transfer efficiency is up to 92.3%. The good thermal quenching resistance, high color-rendering index Ra (91.5) and low CCT (4752 K) of the packaged white LED demonstrate that energy transfer of rare earth phosphors is an effective strategy to target tailored optical performance. NMSO:Ce3+,Tb3+ phosphor has potential applications in near-UV chip excited white LEDs as a green-emitting component.

Novel reddish-orange emitting ultraphosphate CaP4O11:Eu3+ phosphor: Synthesis and photoluminescence properties

In the present work, CaP4O11 was explored as a host material of phosphors for solid-state lighting applications for the first time. This ultraphosphate compound doped with Eu3+ ions was prepared via the solid-state reaction in air atmosphere. The photoluminescence properties were investigated under (UV) ray excitation. From a powder X-ray diffraction analysis, structural Rietveld refinement and IR/Raman spectroscopy, the formation of single phase CaP4O11 with a monoclinic structure was confirmed. The spectral distribution of the Eu3+ -doped CaP4O11 ultraphosphate results in an overall orange-red emission due to the non-negligible intensity of the 5D0→7F1 transition. One Eu3+ center was attributed according to the crystal structure and the luminescence characteristics. The luminescence decay curve of CaP4O11:Eu3+ was fitted into a single exponential function and the lifetime was about 3.8 ms. The obtained CaP4O11:Eu3+ phosphors may have a potential application for solid state lighting based on light emitting diodes technology.

Development of dumbbell-shaped La2Si2O7:Eu3+ nanocrystalline phosphors for solid-state lighting applications

There are ongoing efforts to develop novel phosphors with the properties required to make an object look as natural as it does under sunlight. It has been proven that particle morphology influences the luminescent properties of a phosphor. The rare-earth pyrosilicates, such as La2Si2O7 (LSO) are currently regarded as novel promising scintillators and protective pigments because of their good chemical and thermal stabilities. However, to date, there have been no reports available on the definite morphology of the LSO matrix and the precise luminescent properties of the trivalent europium (Eu3+)-doped LSO phosphor. Herein, we report the development of Eu3+-activated dumbbell-shaped LSO nanocrystalline phosphors using a two-step solvothermal and hydrothermal approach. After regrowth, the amorphous natured LSO:Eu3+ precursor was transformed into well-defined LSO:Eu3+ dumbbell-shaped nanocrystalline phosphors (LSO-R:Eu3+) with a pure monoclinic phase. The phase purity was verified by Rietveld refinement analysis. The formation mechanism of the dumbbell-shaped particles was evaluated using surface morphological studies, and the involvement of the crystal splitting mechanism was established. The luminescence spectra revealed robust red emission at 614 nm under ultraviolet (UV) and near-UV excitations. The dipole-dipole interactions between the neighboring Eu3+ ions induced the concentration quenching in LSO host matrix. Chromaticity coordinates (0.645, 0.342) emerged in the reddish-orange region and were comparable to the standard-definition and high-definition digital television coordinates (0.640, 0.330). Therefore, these results indicate that the synthesized LSO-R:Eu3+ dumbbell-shaped nanocrystalline phosphor is a promising auxiliary red component for assembling desired white light-emitting diodes for indoor illuminations.

Synthesis and luminescence properties of La7Ta3W4O30:Dy3+ yellow-emitting phosphor for solid-state lighting applications

This work was the first to synthesize the yellow-emitting phosphor La7Ta3W4O30:Dy3+ via a high-temperature solid reaction. The structure of La7Ta3W4O30:Dy3+ is trigonal crystalline pertaining to the R-3 (No.148) space group. Under 388-nm excitation, the photoluminescence spectrum of the La7Ta3W4O30:0.10Dy3+ sample exhibited four sharp peaks, which were attributed to 4F9/2–6H15/2 (480 nm), 4F9/2–6H13/2 (573 nm), 4F9/2–6H11/2 (658 nm), and 4F9/2–6H9/2 (753 nm) transitions. The optimal doping content of Dy3+ was 10 mol%, and the critical transfer distance (Rc) of the energy transfer between Dy3+ reached 22 A. The concentration quenching mechanism involved the dipole–dipole interaction. The quenching temperature was higher than 450 K. The fabricated white light-emitting diode (W-LED) possesses a high color rendering index (Ra = 88), good correlated color temperature (5710 K), and chromaticity coordinates (0.328, 0.335) that are close to those of standard white light (0.333, 0.333). Therefore, this prepared phosphor is a potential candidate for W-LED applications.

Effect of Eu3+ ion concentration on the structural and photoluminescence properties of Ba1.3Ca0.7SiO4 ceramic-based red phosphors for solid-state lighting applications

In this study, Ba1.3Ca0.7SiO4: Eu3+ red-orange phosphors were synthesized by the solution combustion method. The effect of varying Eu3+ molar percentages on the material properties including its intrinsic quantum efficiency (IQE) was investigated. XRD results showed synthesized phosphor is hexagonal T-phase Ba1.3Ca0.7SiO4 and the average crystallite size calculated using the Scherer’s formula was estimated to be ∼33 nm. SEM result showed the synthesized Ba1.3Ca0.7SiO4: Eu3+ phosphor had granular shaped and slightly agglomerated particles. The EDS shows that prepared samples contain Ba, Ca, Eu, Si, and O as expected. UV–vis measurement confirms the percent reflectance in the UV- region to be dependents on Eu3+ ions and the estimated bandgap vary between 3.80 and 4.23 eV. Photoluminescence emission measurements of all prepared samples at room temperature appeared to be entirely from inter configurational Eu3+ emission and depend both on the site symmetry as well as ion concentration. Hence, the peak centred at 592 nm is due to transition 5D0 →7F1, while the peak centred at 615 nm is due to transition 5D0 →7F2. The quadrupole-quadrupole multipolar interaction was found to be exclusively responsible for luminescence quenching. The Judd-Ofelt intensity parameters (Ω2, Ω4), asymmetry ratio (R0), and average decay lifetime of the nanocrystals showed dependence on concentration. High IQE values were obtained at low Eu3+ ion concentrations but the efficiency decreased with increasing ion concentration. The CIE color coordination confirmed that the emitted color fall in the strong orange-red region of the emission spectrum.

Sol–gel synthesis of CaLa2(MoO4)4:2xSm3+ microparticles: a red-emitting phosphor with splendid thermal stability for near-ultraviolet-based white light-emitting diodes

We dealt with the synthesis and photoluminescence (PL) behaviors of the Sm3+-activated CaLa2(MoO4)4 phosphors. Under 404 nm irradiation, the prepared samples emitted the visible red emissions from the intra-4f transitions of Sm3+ ions. The color coordinate and color purity of the achieved red emissions were (0.629, 0.370) and 78.2%, respectively. The PL-emission intensity was revealed to dependent on the dopant concentration and the optimal value was 3 mol%. By means of the theoretical calculation, it was found that the involved concentration quenching mechanism was dominated by the dipole–dipole interaction and the critical distance was 40.69 A. Furthermore, the thermal quenching performance of the resultant phosphors was examined utilizing the temperature-dependent PL-emission spectra and the activation energy was decided to be 0.122 eV. Ultimately, through integrating the synthesized phosphors with a commercial near-ultraviolet chip, a red-emitting light-emitting diode was packaged to explore the feasibility of the Sm3+-activated CaLa2(MoO4)4 phosphors for solid-state lighting applications.

A Facile Method Using a Flux to Improve Quantum Efficiency of Submicron Particle Sized Phosphors for Solid-State Lighting Applications

This work successfully verified that the addition of a flux (NH4F, NH4Cl, and H3BO3) during synthesis has an impact on the crystallite size and quantum efficiency of submicron-sized particles of CaMgSi2O6:Eu2+ phosphors. The addition of NH4F or NH4Cl increased the crystallite size in the submicron-sized particles, yielding an increase in emission intensity and quantum efficiency. On the other hand, the use of the H3BO3 flux crystallized a secondary phase, SiO2, and changed the lattice parameters, which degraded the luminescent properties. In addition, an excessive amount of NH4Cl was examined, resulting in nucleation of a secondary phase, CaSiO3, which changed the lattice parameters with no improvement in luminescent properties. These results demonstrate that the addition of a flux could be a method to improve the quantum efficiency of submicron-sized particles composed of nanocrystallites; however, a judicious choice of the flux composition and amount has to be carefully considered.

Citrate-based sol–gel synthesis and luminescent properties of Y6WO12:Eu3+, Dy3+ phosphors for solid-state lighting applications

The rare-earth ions (Eu3+, Dy3+) doped Y6WO12 phosphors were prepared by a citrate-based sol–gel method. The morphologies and structural properties of the as-prepared and doped samples were analyzed by scanning electron microscope images and X-ray diffraction patterns. The luminescent properties were studied by examining the excitation and emission spectra of the samples. The Eu3+ and Dy3+ ions doped samples exhibited their characteristic emission bands in the visible region under ultraviolet light excitation. The temperature-dependent photoluminescence (PL) properties of the samples were also investigated. The PL spectra of the synthesized samples by the sol–gel method were compared with those of the bulk sample prepared by a solid-state reaction. Similarly, the Commission International de I’Eclairage chromaticity coordinates and the decay times of Y6WO12:Eu3+ (3mol%) and Y6WO12:Dy3+ (2mol%) phosphors were studied.

Laser excitation of red, green, blue and trichromatic white rare-earth phosphors for solid-state lighting applications

Phosphors for solid-state lighting, based on a number of different compositional schemes and driven by light from blue light-emitting diodes (LEDs) are widely used for lighting applications. The low efficiency of pump LEDs at high drive currents (droop effect) limits the amount of light produced by conventional LED and phosphor combination. Pumping with laser diodes (LDs) can circumvent this limitation. In this paper we report on the characterisation of individual and a mixture of KEu(WO4)2 (red), BaMg2Al16O27:Eu, Mn (green) and (Sr,Mg)2SiO4:Eu (blue) phosphors, excited by a CW-driven LD operating at 404nm. The activator ion in each of these phosphors is, respectively, Eu3+, Mn2+ and Eu2+. Characteristics of light produced with each phosphor, variations with incident light power and phosphor temperature as well as effects from phosphor ageing are described. Results of comparison between pumping with coherent and incoherent light at the same wavelength are also described.