Solid-state Lighting Research Articles

Robust luminescent material with superior color purity: Sm3+ ion-doped CaAl4O7 phosphor synthesized in a cost-effective approach for solid-state lighting applications

This work reports the synthesis of Sm3+ ion doped calcium dialuminate phosphor by microwave-assisted combustion synthesis technique. Phase purity and the crystal structure of the phosphors were affirmed by PXRD analysis and was found to have monoclinic structure. SEM study was performed to analyze the surface morphology. FTIR study clarifies the existence of functional groups. The optical bandgap of 4.43 eV was determined for CaAl4O7:Sm3+ (x = 0.03) sample. The emission spectra of the sample recorded upon excitation at 403 nm suggest orange color emission around 601 nm pertaining to the transition 4G5/2→6H7/2 of Sm3+ ions. The optimal dopant concentration was established at 3 mol%. CIE chromaticity coordinates of (x = 0.6029, y = 0.3964) were established for the optimized sample. Correlated color temperature of 1620 K demonstrates the emission of light in warmer region. The superior color purity of 99.21 % and color rendering index of 77 for the optimized phosphor material was manifested. The photoluminescence (PL) decay time (for Sm3+ concentration = 0.03 mol) was found to be 0.73 ms. Thermal stability of the sample was investigated and the activation energy was determined to be 0.152 eV by temperature-dependent PL study. To explore the lighting ability of the phosphor, phosphor-in-glass (P-i-G) material was fabricated. CaAl4O7:Sm3+ (x = 0.03) based P-i-G material validates excellent luminous efficacy (360 lm/W) and luminous efficiency (52.70 %) which affirms its practical applications.

Electronic Properties of Group-III Nitride Semiconductors and Device Structures Probed by THz Optical Hall Effect.

Group-III nitrides have transformed solid-state lighting and are strategically positioned to revolutionize high-power and high-frequency electronics. To drive this development forward, a deep understanding of fundamental material properties, such as charge carrier behavior, is essential and can also unveil new and unforeseen applications. This underscores the necessity for novel characterization tools to study group-III nitride materials and devices. The optical Hall effect (OHE) emerges as a contactless method for exploring the transport and electronic properties of semiconductor materials, simultaneously offering insights into their dielectric function. This non-destructive technique employs spectroscopic ellipsometry at long wavelengths in the presence of a magnetic field and provides quantitative information on the charge carrier density, sign, mobility, and effective mass of individual layers in multilayer structures and bulk materials. In this paper, we explore the use of terahertz (THz) OHE to study the charge carrier properties in group-III nitride heterostructures and bulk material. Examples include graded AlGaN channel high-electron-mobility transistor (HEMT) structures for high-linearity devices, highlighting the different grading profiles and their impact on the two-dimensional electron gas (2DEG) properties. Next, we demonstrate the sensitivity of the THz OHE to distinguish the 2DEG anisotropic mobility parameters in N-polar GaN/AlGaN HEMTs and show that this anisotropy is induced by the step-like surface morphology. Finally, we present the temperature-dependent results on the charge carrier properties of 2DEG and bulk electrons in GaN with a focus on the effective mass parameter and review the effective mass parameters reported in the literature. These studies showcase the capabilities of the THz OHE for advancing the understanding and development of group-III materials and devices.

Unveiling highly sensitive Dy3+ doped BaMgAl10O17 phosphor’s thermoluminescence trap features and temperature dependent luminescence for solid state lighting applications

This article explores the structural, morphological, thermoluminescence, and temperature-dependent emission properties of novel Dy3+ doped BaMgAl10O17(BAM-Dy) phosphors. Structural studies reveal that the phosphor has a similar structure to β-alumina. Rod-shaped interlinked surface morphology is a notable characteristic of the BAM-Dy samples. Incorporation of Dy3+ ions lead to the formation of distinct emission peaks (485 nm, 577 nm, and 635 nm) in the PL emission spectra. The effect of dopant concentration on the light output is crucial, and the highest PL intensity is observed for 1.5 mol% of Dy3+ concentration. The potential use of BAM-Dy phosphors for Gamma radiation detection and measurement is tested through thermoluminescence studies, which reveal high sensitivity, low threshold dose values, and exceptional response to low gamma doses, making them suitable for dosimetry applications. The investigation of trap parameters provides useful information about the number of traps, trapping mechanism, and trap energies, which is essential for in-depth study of synthesized phosphors for γ dosimetry application. The study of the effect of temperature on the luminescence behaviour is crucial for the application of phosphors in the light-emitting field. The BAM-Dy samples exhibit excellent thermal stability even at 210 °C, making them suitable for use in the field of White LEDs.

Photoluminescence emission enhancement in the LiSrVO4:Eu3+ vanadate phosphor by partial substitution of M+ ions (M+=Li+/Na+/K+); optical thermometry; and optical transition probabilities using Judd-Ofelt analysis

In solid state lighting (SSL), pcWLEDs gain more attention for various illumination applications. The Eu3+ activated LiSrVO4:xEu3+ (0–15 mol% in steps of 3) phosphors are prepared by the conventional solid state method and their phase formation is confirmed by PXRD. It suggest that the samples are in a monoclinic structure with P2/m space group. SEM results confirmed that the size of the prepared phosphor is in a micrometer range with an irregular spherical shape. The optical diffuse reflectance spectrum (DRS) consisted broad band absorption in the ultraviolet (UV) region (270–350 nm) and also, they are found to absorb strongly the NUV light (396 nm) and the blue light (466 nm). They exhibit the strongest emission at 617 nm for the samples under 326 nm excitation. The PL intensity of the phosphors are improved by co-doping. The optical transition probabilities of the LiSrVO4:9 mol% Eu3+ phosphor are also analyzed using the Judd-Ofelt theory. The optimized phosphor showed a good thermal stability and the lifetime values are in the millisecond range. The absolute and the relative sensitivities are obtained from the temperature dependent lifetime measurements. The LiSrVO4:9 mol%Eu3+ phosphor yielded CIE coordinates (x, y) of (0.5987, 0.4005), a low CCT of 1468K, and a color purity of 96.4 %. These results indicate the potential application of the LiSrVO4 based phosphors in WLEDs.

Concentration-dependent luminescence characterization of terbium-doped strontium aluminate nanophosphors.

The present investigation describes the synthesis of luminescent terbium-doped strontium aluminate nanoparticles emitting bright green light, which were synthesized through a solid-state reaction method assisted by microwave radiation. Various samples containing different concentrations of Tb were synthesized, and an analysis of their structural and morphological features was conducted using powder x-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The band gaps of the samples were determined utilizing the Kubelka-Munk method. The quenching mechanism observed was identified to be due to dipole-dipole interaction using the Dexter theory. The optimized sample with a terbium concentration of 4at.% has a luminescence lifetime of 1.05 ms with 20.62% quantum efficiency. The results of this study indicate that the terbium-doped strontium aluminate fluorescent nanoparticles exhibit promising potential for a wide range of applications, including bioimaging, sensing and solid-state lighting.

Behaviour quantification of Sm3+ in borotellurite glass phosphors for warm-colour illumination

Lighting in unconventional environments is closely related to eye health and circadian rhythms, making it essential for warm-colour light sources to align with technological advancements in solid-state lighting. Herein, warm light in spectral region over 550 nm is realised in Sm3+ doped multicomponent borotellurite (MBT-Sm) glass phosphors as colour converters for LEDs/LDs and their luminescent behaviours are quantified in detail. MBT-Sm glass phosphors standout for their high transparency and the large absorption/emission cross-section, with high quantum efficiency of 84.1 % and quantum yield of 19.15 % under violet LED excitation, and a high luminous flux of 3.33 lm under 50 mW laser. Remarkably, it not only possesses superior colour performance with the correlated colour temperature below 2000 K and colour purity up to 99.8 %, but also shows excellent heat resistance of luminescence. MBT-Sm glass phosphors show promising applications as colour conversion materials in innovative lighting technology.

Synthesis and photoluminescence properties of reddish-orange Li6ALa2Sb2O12:Sm3+ (A = Ca and Sr) garnet phosphors

Single-cubic-phase garnet phosphors of the trivalent samarium (Sm3+)-doped Li6CaLa2Sb2O12 and Li6SrLa2Sb2O12 matrices were investigated with respect to their crystal structure, morphology, and photoluminescence properties. The concentration quenching mechanism dominated by the dipole-dipole interaction determined the 5 mol% Sm3+ as the optimal doping concentration for the Li6ALa2Sb2O12:Sm3+ (A = Ca and Sr) garnet phosphors. As such, the performance comparison was carried out between Li6CaLa2Sb2O12:0.05Sm3+ and Li6SrLa2Sb2O12:0.05Sm3+ garnet phosphors in terms of various aspects (e.g., photoluminescence emission intensity, color purity, thermal stability, photoluminescence quantum yield, and decay curve). Particularly, the emission intensity of the Li6SrLa2Sb2O12:0.05Sm3+ was stronger than the Li6CaLa2Sb2O12:0.05Sm3+ phosphor. Interestingly, both Li6SrLa2Sb2O12:0.05Sm3+ and Li6CaLa2Sb2O12:0.05Sm3+ garnet phosphors exhibited beneficial thermal stability of 67.72 % and 61.67 % at 423 K, respectively. Overall, it is the first report to study and compare the photoluminescence performances of the reddish-orange Li6ALa2Sb2O12:Sm3+ (A = Ca and Sr) garnet phosphors. The findings of this work aim to design a thermal-stable garnet phosphor for potential solid-state lighting.

Spectroscopic study of yellowish white light emitting MgP2O6: Dy3+ phosphor

A yellowish white light emitting Dy3+ (0.5, 1, 1.5, 2, and 2.5 mole%) activated MgP2O6 phosphors were prepared using Solution combustion (SC) method. The X-ray diffraction (XRD) and Rietveld refinement confirmed the phase purity with “monoclinic symmetry” having space group P21/n. The lattice constant of the optimum doped sample is also refined by “Full Prof software”. Photoluminescence (PL) spectroscopy was employed to observe the luminescent properties, including both excitation and emission features. The phosphor verified intense yellowish emission at 573 nm, analogous to the hypersensitive electric dipole transition4F9/2→6H13/2. The critical activated concentration of MgP2O6:Dy3+ phosphor approximately occurs at 1.5 mole%. The phosphor exhibits conventional applications in solid-state lighting when excited under UV light at 348 nm.

Shelf-Stable Green and Blue Quantum Dot Light-Emitting Diodes with High Efficiencies.

Quantum dot light-emitting diodes (QLEDs) are promising electroluminescent devices for next-generation display and solid-state lighting technologies. Achieving shelf-stable and high-performance QLEDs is crucial for their practical applications. However, the successful demonstration of shelf-stable QLEDs with high efficiencies is limited to red devices. Here, we developed a solution-based amine ligand exchange strategy to passivate the surfaces of optical ZnO (O-ZnO) nanocrystals, leading to suppressed exciton quenching at the green and blue QD/oxide interface. Furthermore, we designed new bilayered oxide electron-transporting layers consisting of amine-modified O-ZnO/conductive ZnO. This design simultaneously offers suppressed interfacial exciton quenching and sufficient electron transport in the green and blue QLEDs, resulting in shelf-stable green and blue devices with high efficiencies. Our devices exhibit neglectable changes in external quantum efficiencies (maximum external quantum efficiencies of 22.4% for green and 14.3% for blue) after storage for 270 days. Our work represents a step forward in the practical applications of QLED technology.

Fabrication and luminous properties of BaAl2O4-LuAG:Ce composite phosphor ceramics for solid-state laser lighting

Based on the “effective ionic radius match effect” and the “charge balance substitution rule of ions”, mixed Ba2+, Al3+, Lu3+, and Ce3+ ions can be effectively regulated to a BaAl2O4-LuAG:Ce biphasic structure. The contribution of BaAl2O4 like as scattering centers can reduce overall reflection losses and enhance the light extraction efficiency of these composite phosphor ceramics (CPCs). In this work, a series of x wt.% BaAl2O4-LuAG:Ce (x = 0, 3, 5, 10, 15) CPCs were fabricated by vacuum sintering using co-precipitated composite powders. Homogenization at the atomic level of mixed Ba3+, Al3+, Lu3+, and Ce3+ ions in multiphase powders provides uniform distribution of BaAl2O4 and LuAG:Ce constituent phases in composite ceramics. The introduction of BaAl2O4 has an additive effect, which also consists in uniform aggregation of pores near their grains during sintering. It allows to adjust the size and amount of microstructural defects by varying the secondary phase content. Under the excitation of 10.8 W 450 nm LDs in a reflection mode, 3 wt% BaAl2O4-based CPCs show the optimum luminous flux of 2244 lm and a luminous efficiency of 208 lm·W−1. The obtained CPCs show a high application potential in solid-state laser lighting.

Energy Efficiency in Public Lighting Systems Friendly to the Environment and Protected Areas

Solid-state lighting technology, such as LED devices, is critical to improving energy efficiency in street lighting systems. In Ecuador, government policies have established the obligation to exclusively use LED systems starting in 2023, except in special projects. Ecuador, known for its vast biodiversity, protects its national parks, which are rich in flora, fauna and natural resources, through international institutions and agreements such as UNESCO, CBD and CITES. Although reducing electrical consumption usually measures energy efficiency, this article goes further. It considers aspects such as the correlated color temperature in the lighting design of protected areas, light pollution and the decrease in energy quality due to harmonic distortion. Measurements of the electromagnetic spectrum of the light sources were made in an area in the Galápagos National Park of Ecuador, revealing highly correlated color temperatures that can affect ecosystem cycles. In addition, the investigation detected levels of light pollution increasing the night sky brightness and a notable presence of harmonic distortion in the electrical grid. Using simulations to predict the behavior of these variables offers an efficient option to help preserve protected environments and the quality of energy supply while promoting energy savings.

Enhanced red emission of Er3+ ion by cooperative sensitization of Sb3+ and Yb3+ ions in β-NaYF4 microcrystals under 376 nm excitation

A series of Sb3+/Yb3+/Er3+ doped β-NaYF4 microcrystals were prepared via a hydrothermal method. With the increase of the concentration of Sb3+ ion, the red emission of Er3+ ion in Sb3+/Yb3+/Er3+ doped β-NaYF4 microcrystals was enhanced under 376 nm ultraviolet light excitation. However, Sb3+ ion can decrease the green and red emission of Er3+ in Sb3+/Er3+ double-doped β-NaYF4 microcrystals. Therefore, cooperative sensitization of Sb3+ and Yb3+ ions was observed in Sb3+/Yb3+/Er3+ tri-doped β-NaYF4 microcrystals for the first time. The possible energy transfer processes of Er3+→Sb3+→Yb3+→Er3+ under 376 nm ultraviolet light excitation were first proposed. These newfound processes can provide more research perspectives to explore the energy transfer relationships among Sb3+, Yb3+ and Er3+ ions. Furthermore, the stronger red emission has great potential applications in agricultural solid-state lighting and photovoltaic cell. And the CIE coordinate of β-NaYF4: 20 mol%Yb3+, 2 mol%Er3+, 30 mol%Sb3+ microcrystal under 376 nm excitation is (0.3206, 0.3307), which can be used as an excellent candidate for white light emitting diodes phosphor.

Effect of Li+ on luminescence properties and thermal stability of glass ceramics containing SrMoO4

Dy3+, Eu3+ co-doped glass ceramics (GCs) containing SrMoO4 crystalline phase were prepared by melt-curing-crystallization method. The most favorable heat treatment conditions for the glass ceramics were found to be 610 °C/2 h by differential scanning calorimetry (DSC), ultraviolet spectrophotometer (UV–Vis), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The best doping concentrations of Dy3+ and Eu3+ in this glass ceramic were 0.8 % and 0.6 %, concentration quenching caused by dipole-dipole interactions occurs when the content of rare earth ions in GCs continues to increase. The chromaticity coordinates of the Dy3+- Eu3+ co-doped glass ceramics changed from cool white light to warm white light with the addition of Eu3+ concentration. At the optimal doping concentration (0.8 % Dy3+-0.6 % Eu3+), the chromaticity coordinate of glass ceramics is (0.3972, 0.3331), and the related color temperature is 3047 K. The luminescence intensity can still reach about 80 % of room temperature at 180 °C, and its thermal quenching activation energy is 0.233 eV. This suggests that glass ceramics have excellent thermal stability. After adding an appropriate amount of Li+, the crystalline phase of the glass ceramics remained unchanged and the luminous intensity of the glass ceramics increased by a factor of about 1.4 in the same environment. The thermal quenching activation energy of the glass ceramic doped with 0.2 % Li+-0.8 % Dy3+-0.6 % Eu3+ was 0.344 eV. The experimental results indicate that GCs has potential application prospects in the field of solid-state lighting.

Yellowish light emitting Dy3+ doped single phase – BaNb2O6 phosphors for solid state lighting applications

BaNb2O6:Dy3+ phosphors that emit cool light has been synthesized via traditional solid-state reaction technique. Developed samples show orthorhombic structure with space group C2221 according to X-Ray Diffraction (XRD) and Rietveld structural refinement. Observations made using a scanning electron microscope (SEM) show densely packed particles with irregular shapes in the micrometre range. Optical bandgap was also determined using Diffuse Reflectance Spectroscopy (DRS). When excited at 389 nm, the as-prepared phosphors show blue (481 nm) and yellow (577 nm) emissions, which correspond to the 4F9/2 → 6HJ (J = 15/2, 13/2) transitions of Dy3+ ions. A thorough investigation has been done on the energy transfer process between Dy3+ ions. The optimized phosphor's computed chromaticity coordinates for the Commission Internationale de L'Eclairage (CIE) are x = 0.392 and y = 0.414. The values of CIE chromaticity coordinates and correlated colour temperature (CCT) of 3995 K endorse near cool light emission from the phosphor. Thermal stability and temperature dependent photoluminescence spectroscopy were studied for optimized phosphor which revealed that the phosphor can be a potential material for lighting applications at higher temperature. The study also reveals that BaNb2O6:Dy3+ phosphor could be a promising candidate for near ultra-violet (NUV) excited, yellowish LED applications.

Binary Host-induced Exciplex Enabled High Color-Rendering Index of 94 for Carbon Quantum Dot-Based White Light-Emitting Diodes.

White light-emitting diodes (WLEDs) with high color-rendering index (CRI, >90) are important for backlight displays and solid-state lighting applications. Although the well-developed colloidal quantum dots (QDs) based on heavy metals such as cadmium and lead are promising candidates for WLEDs, the low CRI still remains a significant limitation. In addition, the severe toxicity of heavy metals greatly limits their widespread use. Herein, the study demonstrates low-cost and environmentally friendly carbon quantum dots (CQDs)-based WLEDs that exhibit a high CRI of 94.33, surpassing that of conventional cadmium/lead-containing QD-based WLEDs. This achievement is attained through the employment of a binary host-induced exciplex strategy. The high hole/electron mobility and suitable energy levels of the donor and acceptor give rise to a broadband orange-yellow emission stemming from the exciplex. As the host, the binary exciplex is capable of contributing blue and orange-yellow emission components while efficiently mitigating the aggregation-induced quenching of CQDs. Meanwhile, CQDs effectively address the deep-red emission gap, enabling the realization of CQDs-based WLEDs with high CRI. These WLEDs also exhibit a remarkably low turn-on voltage of 2.8V, a maximum luminance exceeding 2000cd m- 2, a correlated color temperature of 4976 K, and Commission Internationale de l'Eclairage coordinates of (0.34, 0.32).

Win, lose, or draw? Forecasting the outcome of a race toward a dominant formal standard with machine learning

Accurate forecasting of the outcome of a race toward a dominant formal standard can help companies make informed decisions and develop appropriate strategies to achieve market leadership. This paper focuses on factors contributing to formal standards dominance and applies machine learning (ML) methods to predict which standard supporters will win in formal standard battles. The empirical context is the de jure standard-setting process in the Chinese solid-state lighting (SSL) industry. We employ 1011 valid sample datasets from 1998 to 2016. Our findings reveal that the random subspace (R.S.)-MultiBoosting approach outperforms the other three approaches regarding forecasting outcomes, especially when dealing with small datasets. Strong tie strength in standard supporting alliances, prior experience in patent application, and an appropriate level of marketization can enhance firms' chances of winning dominant formal standards.

Rare-Earth-Metal-Free Solid-State Fluorescent Carbonized-Polymer Microspheres for Unclonable Anti-Counterfeit Whispering-Gallery Emissions from Red to Near-Infrared Wavelengths.

Colloidal carbon dots (CDs) have garnered much attention as metal-free photoluminescent nanomaterials, yet creation of solid-state fluorescent (SSF) materials emitting in the deep red (DR) to near-infrared (NIR) range poses a significant challenge with practical implications. To address this challenge and to engineer photonic functionalities, a micro-resonator architecture is developed using carbonized polymer microspheres (CPMs), evolved from conventional colloidal nanodots. Gram-scale production of CPMs utilizes controlled microscopic phase separation facilitated by natural peptide cross-linking during hydrothermal processing. The resulting microstructure effectively suppresses aggregation-induced quenching (AIQ), enabling strong solid-state light emission. Both experimental and theoretical analysis support a role for extended π-conjugated polycyclic aromatic hydrocarbons (PAHs) trapped within these microstructures, which exhibit a progressive red shift in light absorption/emission toward the NIR range. Moreover, the highly spherical shape of CPMs endows them with innate photonic functionalities in combination with their intrinsic CD-based attributes. Harnessing their excitation wavelength-dependent photoluminescent (PL) property, a single CPM exhibits whispering-gallery modes (WGMs) that are emission-tunable from the DR to the NIR. This type of newly developed microresonator can serve as, for example, unclonable anti-counterfeiting labels. This innovative cross-cutting approach, combining photonics and chemistry, offers robust, bottom-up, built-in photonic functionality with diverse NIR applications.

Effect of Mn2+ Doping on the Photoluminescence of Hybrid One-Dimensional Lead Halide Post-Perovskites.

Although organic-inorganic hybrid one-dimensional (1D) lead halide postperovskites (LHPPs) have been reported to show white luminescence and tunable photoluminescence quantum yield (PLQY), their structure-property relationships are not fully understood. Here, we used Mn2+ to test the doping effect on the luminescence of two 1D-LHPPs compounds, namely, {TETA[Pb2Br6]}n 1 and {TETA[Pb2Cl6]}n 2, where TETA = triethylenetetrammonium. We found the pristine compounds show yellowish (551 nm) and bluish (447 nm) emission for 1 and 2, respectively, nanosecond excitation lifetimes (4.17 ns for 1 and 2.29 ns for 2) and low PLQYs (4.65 and 3.57% for 1 and 2, respectively). By fine-doping the Mn2+ ions to ca. 8% the PLQYs for 1 and 2 are maximized to 24 and 25% for 1 and 2, respectively. Upon the increasing Mn2+ dopant, the emission wavelengths can also vary gradually from 551 to 615 nm and from 447 to 660 nm for 1 and 2, respectively, covering almost the whole visible-light range, and the excitation lifetimes are enhanced to microseconds (0.77 μs for 1 and 0.39 μs for 2), owing to the more spin-forbidden d-d transition (4T1-6A1) component from the Mn2+ ions present in the photoluminescence spectra. Moreover, these Mn2+-doped 1D-LHPPs demonstrate high structural and optical stability in humid and high-temperature environments. Hence, such doped materials can be fabricated into a UV-pumped white light-emitting diode, rendering the potential application for solid-state lighting and display systems.

Green-Emitting Perovskite BaTiO3:Ho3+ Phosphors for Solid-State Lighting

Green-Emitting Perovskite BaTiO3:Ho3+ Phosphors for Solid-State Lighting

Spectroscopic evaluation of gold nanoparticles-embedded Dy3+-doped Li2CO3–SrO–ZnO–B2O3 glasses: white solid-state lighting potential

Spectroscopic evaluation of gold nanoparticles-embedded Dy3+-doped Li2CO3–SrO–ZnO–B2O3 glasses: white solid-state lighting potential