Solid-state Lighting Applications Research Articles

Dy3+ doped KCa(PO3)3 phosphor for white light generation: structural and luminescent studies

Abstract Using the traditional solid-state reaction approach, Dy3+ ions doped KCa(PO3)3 phosphors have been synthesized to investigate their luminescent properties to produce high-quality white light for solid-state lighting applications, particularly in white LEDs. X-ray diffraction (XRD) patterns were used to examine the structure and phase of the phosphors. Using scanning electron microscopy (SEM), the morphology of the as-synthesized phosphor has been investigated. Fourier transform infrared spectroscopy (FT-IR) has been used to investigate several vibrational bands seen in the phosphor. Using diffuse reflectance spectra (DRS), the as-synthesized phosphors' optical band gap values have been estimated. When Dy3+ ions are excited at 350 nm, the photoluminescence (PL) spectra characteristics observed for the activated KCa(PO3)3 phosphor show strong white area emission at 575 nm, which is related to the 4F99/2 → 6H13/2 transition of Dy3+ ions. Additionally, the concentration quenching of Dy3+ ions doped at 4 mol% is seen in the PL spectra. Based on the observed PL spectra, the computed CIE chromaticity coordinates for the doped KCa(PO3)3 phosphors show that the optimised 4.0mol% Dy3+ doped phosphor is located in the deep white area. The lifespan of the as-titled phosphors decreases as the amount of Dy3+ ions increases in the host lattice. Additionally, the PL decay profiles shows a dual exponential behaviour when excited at 350 nm, with an emission wavelength at 575 nm. On the basis of the results of the aforementioned studies, we wish to project Dy3+ ion doped KCa(PO3)3 phosphors as white light generating materials in w-LEDs and for other photonic applications.

Construction of Interfacial Energy Transfer Nanoplatforms Using Carbon Dots and NaYF4:Eu3+ Nanoparticles

Förster resonant energy transfer (FRET) is a well-known and important phenomenon in physics, chemistry, and biology, which plays a crucial role in various photofunctional systems, including photovoltaics, and lighting, and sensing where molecular distances and interactions are probed. This paper presents a systematical investigation of the construction of interfacial FRET between carbon dots (CDs) and NaYF4:Eu3+ nanoparticles (NPs) via various synthesis routes. The interfacial FRET was found to take place from CDs to Eu3+ in the wet-mixed and the reacted nanocomposites owing to the presence of strong interfacial interactions, as evidenced by the results of Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) results. By employing CDs-sensitized NaYF4:Eu3+ NPs as a model system, we were able to elucidate the intricate FRET mechanism between CDs and NaYF4:Eu3+ NPs. Surprisingly, the reacted nanocomposite exhibits remarkable photo- and thermal-stability, as well as high resistance to thermal degradation, demonstrating the robustness of the interfacial FRET in enhancing Eu3+ emission intensity. The study presents a convenient and versatile approach to achieving interfacial FRET based on CDs nanocomposites, which have a promising potential application in solid-state lighting and biomedicine.

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

Efficiently green-emitting and ultra-stable CsPbBr3@SiO2 nanocomposites for white light-emitting diodes

Inorganic oxide especially SiO2 encapsulation strategy is an effective way to improve the stability of all-inorganic cesium lead halide perovskite (CsPbX3, X = Cl, Br, I) nanocrystals (NCs). However, when CsPbX3 NCs are encapsulated in SiO2 by in situ tetraethyl orthosilicate (TEOS) hydrolysis, the unavoidable by-products (water and ethanol) of TEOS hydrolysis commonly damage the structural and optical properties of the CsPbX3 NCs. Herein, TDPA-CsPbBr3 NCs with the dense tetradecylphosphonic acid (TDPA) passivation were pre-prepared and subsequently encapsulated into SiO2 via in situ TEOS hydrolysis. Benefitting from the dense phosphonic passivation layer capable of resisting the erosion of polar by-products generated by TEOS hydrolysis, the obtained TDPA-CsPbBr3@SiO2 nanocomposites maintain the excellent optical properties of the colloidal CsPbBr3 NCs, showing near-unity photoluminescence quantum yield (PLQY) and ultra-narrow full width at half maximum (FWHM). Furthermore, the TDPA-CsPbBr3@SiO2 nanocomposites exhibit outstanding stability against ethanol, UV light, and heating treatment due to the dual protection of dense phosphonate ligand layers and inorganic SiO2 matrix. The white light-emitting diodes (WLED) device was fabricated by sequentially depositing green-emitting TDPA-CsPbBr3@SiO2 nanocomposites and red-emitting K2SiF6:Mn on blue-emitting GaN LED chip. The obtained WLED exhibits excellent luminous performances with standard white emission of CIE Coordinates (0.33, 0.33), a color gamut 138 % of the NTSC and 103 % of Rec. 2020, respectively. This study demonstrates that TDPA-CsPbBr3@SiO2 nanocomposites have a potential application in solid-state lighting and backlight displays.

Interlaboratory Comparison on Absolute Photoluminescence Quantum Yield Measurements of Solid Light Converting Phosphors with Three Commercial Integrating Sphere Setups.

Scattering luminescent materials dispersed in liquid and solid matrices and luminescent powders are increasingly relevant for fundamental research and industry. Examples are luminescent nano- and microparticles and phosphors of different compositions in various matrices or incorporated into ceramics with applications in energy conversion, solid-state lighting, medical diagnostics, and security barcoding. The key parameter to characterize the performance of these materials is the photoluminescence/fluorescence quantum yield (Φf), i.e., the number of emitted photons per number of absorbed photons. To identify and quantify the sources of uncertainty of absolute measurements of Φf of scattering samples, the first interlaboratory comparison (ILC) of three laboratories from academia and industry was performed by following identical measurement protocols. Thereby, two types of commercial stand-alone integrating sphere setups with different illumination and detection geometries were utilized for measuring the Φf of transparent and scattering dye solutions and solid phosphors, namely, YAG:Ce optoceramics of varying surface roughness, used as converter materials for blue light emitting diodes. Special emphasis was dedicated to the influence of the measurement geometry, the optical properties of the blank utilized to determine the number of photons of the incident excitation light absorbed by the sample, and the sample-specific surface roughness. While the Φf values of the liquid samples matched between instruments, Φf measurements of the optoceramics with different blanks revealed substantial differences. The ILC results underline the importance of the measurement geometry, sample position, and blank for reliable Φf data of scattering the YAG:Ce optoceramics, with the blank's optical properties accounting for uncertainties exceeding 20%.

Ratiometric thermometry using down-conversion luminescence and solid-state lighting application of Er3+ activated strontium tungstate phosphor

Er3+ activated Sr3WO6 double perovskite crystallized in triclinic structure was synthesized via the solid-state reaction method at 1200 °C for non-contact optical thermometry and solid-state lighting. The phosphors under study were characterized via X-ray diffraction, scanning electron microscopy, diffusion reflectance spectra, and photoluminescence techniques. When excited with 380 nm, the Sr3WO6:Er3+ phosphors exhibited intense green emission, corresponds to 2H11/2/4S3/2-4I15/2 transitions of Er3+. The fluorescence intensity ratio of thermally coupled energy levels were computed within 303–513 K and subsequent relative sensitivity (0.56% K−1 at 303 K) was determined. Moreover, the PL intensity maintained 76.28% at LED burning temperature (150 °C) compared to PL intensity observed at room-temperature, denotes good thermal stability. Additionally, the fluorescent behaviour of the phosphors was examined via PL decay lifetime study. The PL quantum efficiency of the phosphor is computed via the Auzel's model using PL decay lifetime, and was obtained to be 80.32% for Sr3WO6:2% Er3+ phosphor.

Up-converted white light emission in Er3+ doped MgAl2O4 nanocrystals

This work presents the influence of host defect centers on the photoluminescence characteristics of Mg1−xErxAl2O4 (x = 0.005, 0.01, and 0.03) nanocrystals under UV and near-infrared (NIR) excitations. The spinel-structured nanocrystals are synthesized through the combustion method. The Rietveld refinement and nuclear magnetic resonance analyses estimated the Er3+ ion occupancy at octahedral and other random sites of the MgAl2O4 lattice, and the existence of various lattice defects. Diffuse reflectance spectra showed broad bands attributed to oxygen vacancies as well as antisite defects and sharp peaks attributed to f–f transitions of Er3+ ions. The upconversion luminescence spectra consisted of sharp emission lines, ascribed to Er3+ ions, in the green and red wavelength regions, which overlapped over the broad curve attributed to intrinsic defects. Further, the UV excited downconversion luminescence spectra showed two broad emission bands in blue–violet and red-NIR regions with a very weak Er3+ ion emission feature. This up- and downconversion emission revealed energy transfer between host and Er3+ ions via intrinsic defects. As a result, the emission color changes from bluish purple to white by varying the excitation wavelength from UV to NIR. This rare earth activated luminescence from MgAl2O4 nanocrystals would exhibit potential applications in display devices and solid-state lighting.

Synthesis and photoluminescence properties of Ba3(PO4)2:Eu3+/2+ phosphors

Single-phase phosphors of Ba3–хEu2х/3(PO4)2 (x = 0.01, 0.02) were obtained for the first time using solid-phase synthesis. These phosphors are isostructural to the palmierite mineral. The self-reduction of Eu3+ to Eu2+ in the Ba3(PO4)2 host was observed in air at high temperature. The dependence of luminescence intensity on temperature was studied over a broad range of 80–500 K. The luminescence intensity of Eu3+ is significantly depends on temperature and decreases as the temperature increases, while Eu2+ emission remains stable between 150 and 500 K. Eu3+ ions incorporated into the polyhedra of the M1 sites of the Ba3(PO4)2 structure demonstrated improved thermal stability compared to Eu3+ ions in the polyhedra of the M2 sites. Photoluminescence spectra, when excited at 395 nm, consist of intense bands at 585 nm and 610 nm, typical for Eu3+ cations. When excited at 330 nm, the luminescence spectra display a broad band centered at 425 nm, typical for Eu2+ cations. The resulting orange-red phosphors have potential applications in solid-state lighting.

The 2023 Nobel Prize in Chemistry: Quantum dots

The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Brus (prize share 1/3), and Moungi G. Bawendi (prize share 1/3) for groundbreaking inventions in the field of nanotechnology, i.e., for the discovery and synthesis of semiconductor nanocrystals, also termed quantum dots, that exhibit size-dependent physicochemical properties enabled by quantum size effects. This feature article summarizes the main milestones of the discoveries and developments of quantum dots that paved the road to their versatile applications in solid-state lighting, display technology, energy conversion, medical diagnostics, bioimaging, and image-guided surgery.

Optical properties of blue-light-emitting Y2 O3 :Ce nanophosphor for solid-state lighting application.

The structural, surface morphological, optical absorption and emission features of Y2 O3 :Ce (0%-5%) were studied. The samples had a body-centred cubic crystal structure. The undoped sample had a crystallite size of 29.03 nm, and it varied after doping with Ce. The grain size of the samples varied from 23.00 to 50.78 nm. All the samples exhibited a strong absorption band at 206 nm due to F-centre absorption and absorption involving the delocalised bands. In addition, the doped samples exhibited a secondary band at ~250 nm due to 4f → 5d transitions of Ce3+ ions. The optical bandgap of the undoped sample was found to be ~5.37 eV, and it decreased to 5.20 eV with an increase in Ce concentration to 5%. The undoped sample under 350-nm excitation exhibited a broad photoluminescence (PL) emission band with the maxima at 406 nm and a secondary band at 463 nm. In contrast, multiple PL peaks were centred at ~397, 436, 466, 488 and 563 nm in all the doped samples. The average lifetime of the emission band at 406 nm was 1.05 ns and that of the emission band at ~466 nm was 1.63 ns. The material has potential for solid-state lighting applications.

Enhancing energy transfer via inhibition defect density of coupled quasi-2D perovskite layers for efficient sky-blue light-emitting diodes

Metal halide perovskite materials have emerged as unique and promising candidates for full-color display and solid-state lighting applications. While substantial progress has been made in developing green, red and near-infrared perovskite light-emitting diodes (PeLEDs) with external quantum efficiency (EQE) approaching their theoretical upper limit, the performance of blue PeLEDs is still lagging far behind. Here, synergistic long and short hydrobromide chains are strategically introduced into the perovskite to regulate composition and dimensional engineering for promoting coupled quasi-two-dimensional perovskite thin films with enhanced photoluminescence quantum yield (PLQY) and reduced trap state density. The inclusion of the hydrobromide can also simultaneously passivate the perovskite defects by reducing nonradiative recombination loss and increasing the formation of n >1 phases for efficient exciton energy transfer. Encouraged by these findings, we finally demonstrate the most stable sky-blue PeLEDs to date with a half-lifetime of 515 min at high external quantum efficiency (EQE＞10 %), emitting at 486 nm with a peak EQE of up to 15.6 %.

Efficient Single-Phase Tunable Dual-Color Luminescence with High Quantum Yield Greater than 100% for Information Encryption and LED Applications.

In modern society, the investigation of highly efficient photoluminescent bulk materials with excitation-induced tunable multicolor luminescence and multiexciton generation (MEG) is of great significance to information security and the application of optoelectronic devices. In this study, two bulk Cu-based halide crystals of (C4H10NO)4Cu2Br5·Br and (C4H10NO)4Cu2I5·I·H2O, respectively, with one-dimensional structures were grown by a solvent evaporation method. Unexpectedly, (C4H10NO)4Cu2I5·I·H2O displayed excitation-induced tunable dual-color luminescence; one band is a brilliant green-yellow emission centered at 547 nm with a high photoluminescence quantum yield (PLQY) of up to 169.67%, and the other is a red emission at 695 nm with a PLQY of 75.76%. Just as importantly, (C4H10NO)4Cu2Br5·Br exhibits a strong broadband green-yellow emission at 561 nm under broad band excitation ranging from 252 to 350 nm, a long PL decay lifetime of 106.9 μs, and an ultrahigh PLQY of 198.22%. These materials represent the first two examples of 1D bulk crystals and Cu(I)-based halides that have a PLQY exceeding 100%. Combining the unusual luminescence characteristics with theoretical calculations reveals that MEG contributes to the green-yellow emission with ultrahigh PLQY > 100%, and that the red emission can be ascribed to [Cu2I5]3- cluster-centered emission. Additionally, an information encryption method was designed based on the Morse Code. The high luminescence characteristics of LED devices fabricated using the (C4H10NO)4Cu2Br5·Br and (C4H10NO)4Cu2I5·I·H2O crystals appear to lead to promising applications in solid-state lighting. This work extends the catalog of high-performance luminescent materials and also promotes application prospects of low-dimensional copper-based halides in optoelectronics.

Comparing the influence of cation order and composition in simulated Zn(Sn, Ge)N2 on structure, elastic moduli, and polarization for solid state lighting

Alloying and site ordering play complementary roles in dictating a material’s properties. However, deconvolving the impacts of these separate phenomena can be challenging. In this work, we simulate structures of Zn(Sn,Ge)N2 with varied Sn content and site ordering to determine the impacts of order and composition on structural and electronic properties. We assess the formation enthalpy, lattice parameters, elastic constants, spontaneous polarization, and piezoelectric coefficients. In mostly disordered structures (order parameters ranging from 0.2 to 0.4), the formation enthalpy exhibits local extrema as a function of the order parameter, deviating from the more linear trends seen in both fully disordered and fully ordered systems. This anomalous deviation from the otherwise linear trend in formation enthalpy with order manifests in each of the other properties calculated. This range of order parameters of interest may be caused by a transition in the ordering of the quaternary material similar to phase changes seen in ternary compounds but stretched over a region inclduing 20% of the order parameter range. Most parameters calculated are more sensitive to order than to composition in the limited composition range tested; however, the lattice parameter c, piezoelectric coefficient e33, and elastic moduli C12, C13, and C23 are more sensitive to composition. Of the properties compared, the piezoelectric coefficients are influenced most significantly by changes in both the composition and order parameter. Lattice parameters undergo the smallest changes with order and composition, but these small differences appear to impart large trends in the other properties. Better understanding the effects of disorder and group IV alloying in Zn(Sn,Ge)N2 allows for more accurate modeling of characteristics of this material system for solid state lighting and other applications.

Luminescence of Tm3+, Yb3+ Co-doped CaLaAlO4/LaAlO3 Mixed Phase Phosphor for Solid-state Lighting Application

CaLaAlO4/LaAlO3: 0.5%Tm3+, xYb3+ upconversion phosphors were prepared via the combustion method. The Tm3+ dopant concentration was constant (Tm=0.5mol%), while the concentration of Yb3+ co-dopant was varied (Yb = 1 – 10 mol%). The X-ray diffraction studies indicated a mixture of phases (tetragonal and hexagonal of CaLaAlO4 and LaAlO3 respectively). The optical absorption spectra of the upconversion phosphors have two absorption bands centered at 253 nm, and another band at 440 nm. The band at 253 nm is ascribed to the charge transfer band (CTB) between the ligand (O2-) and Yb3+ ions, while the broad band located at 440 nm was related to defect states in the lattice. The energy bandgap and refractive index of the optimized phosphor were 4.73 eV and 1.76 respectively. The upconversion emission peaks centered at 478 nm (1G4 → 3H6), 654 nm (1G4 → 3F4), and 801 nm (3H4 → 3H6) are associated to the electronic transitions of Tm3+ ions. As the Yb concentration increases, the colour emission is tuned from bluish white to blue light. The CCT and CIE coordinate of (0.2419, 0.2463) showed that the phosphor doped with 10 mol% of Yb3+ produces a bluish-white and its colour purity was 80%. Thus, the strong bluish-white light emission produced by the CaLaAlO4/LaAlO3: 0.5%Tm3+, xYb3+ phosphors could be used for solid-state lighting (SSL) or in multicolour displays.

Blue-Emitting SrLaAlO<sub>4</sub>: Ce Phosphors Obtained by Combustion Synthesis

In this study, a simple combustion synthesis was utilized to obtain the SrLaAlO4 (SLAO) host sample and SrLaAlO4: Ce (SLAO:Ce) phosphors with different Ce concentrations (1.0, 3.0, 5.0 and 7.0 mol.%). Also, the as-synthesized samples were subjected to a post-annealing treatment at 1200 °C in air. X-ray diffraction (XRD) patterns for the SLAO and SLAO:Ce phosphors correspond to pure tetragonal phase (JCPDS No 24-1125). The photoluminescence spectra of the SLAO:Ce phosphors (under 254 nm excitation) showed a blue emission peak at 470 nm attributed to the 5d → 4f Ce3+ transition. The SLAO:Ce phosphors doped with 1 mol.% of Ce showed the highest emission and quenching of photoluminescence was produced when the Ce dopant concentration increases (3.0-7.0 mol.%). The CCT and color purity are in the range of 6456 -8276 K and 49.1 -55.9 % respectively. Due to its strong blue emission, the SLAO:Ce phosphor could be a good candidate for UV phosphor converted LED or for solid state lighting applications.

Green Emission of Erbium Doped SYW Phosphors for Optical Thermometry And Solid‐State Lighting

AbstractA series of Er3+ ions doped Sr9Y2W4O24 (SYW) phosphors have been synthesised using solid‐state reaction technique. For optical thermometry and solid state lighting applications, the crystal structure, morphological, and luminescence features of the SYW : Er3+ phosphors were explored. X‐ray diffraction (XRD) reveal that synthesized phosphors having single phase with a tetragonal crystal structure and I41/a space group. Scanning electron microscopy (SEM) was used to examine the morphological behaviour and presence of composition elements. The optical bandgap of the phosphor was evaluated using UV‐Vis diffuse reflection spectra (DRS). The photoluminescence (PL) emission spectra were captured under 380 nm excitation, and the peak with the maximum intensity was identified at 563 nm ascribed to transition 4S3/2→4I15/2, that emits green color in visible region. The temperature dependent PL (TD‐PL) spectra show that SYW phosphor is substantially more thermally stable, having thermal activation energy of about 0.247 eV. Additionally, the fluorescence intensity ratio (FIR) was used to study the optical sensing characteristics of the thermal quenching transitions (2H11/2, 4S3/2) with maximum relative sensitivity (SR) and an absolute sensitivity (SA) being 1.33 % K−1and 0.307 % K−1, respectively. All of the aforementioned findings demonstrate that SYW : Er3+ ions doped phosphors have potential for optical thermometry and other photonic devices.

Advancements of Lanthanide-doped Phosphors in Solid-state Lighting Applications

Abstract: The challenge of energy conversion and enhancement has been a problem in the world of lighting technologies as the population and global industrialization grow rapidly. Solid-state lighting (SSL) has proven to be a better alternative in the illumination industry because of its environmentally friendly and high energy efficiency. Lanthanide-doped phosphors have gained global attention in SSL because they have versatile applications with enhanced overall performance and luminescence. This review delves into the advancement in lanthanide-doped phosphors for Solid-state lighting (SSL) applications. It discusses the in-depth analysis of how to tailor the crystal lattice design, optimize the host material for emission efficiency, and minimize the non-radiative pathways. This paper further discusses the lanthanide-doped phosphor composition, strategies to obtain desired emission spectra, and enhanced color rendering index with the Energy transfer mechanism and the synthesis techniques. This review also addresses 3 processes for expanding the light spectrum, current challenges, future directions, and emerging trends present in the lanthanide-doped phosphor in Solid-state lighting (SSL) applications.

Synthesis, characterization, and enhanced photoluminescence of ZrO2:Dy3+ phosphors by incorporating Li+, Na+ and K+ ions for LED applications

ZrO2:(0.01)Dy3+:xA+ (A = Li+, Na+ and K+) phosphors were prepared by one step solution combustion method. X-ray diffraction (XRD), reveal formation of different phases. Functional group presence and its vibrations are assigned from FTIR measurements. Influence of alkali metal ions (A+) on surface morphology were realized from SEM micrograph. XPS study was carried out to confirm the presence of Li+ ions. Photoluminescence (PL) spectra of the samples excited at 350 nm exhibited two strong emission peaks at 480 nm and 580 nm, which are characteristic transitions of Dy3+ ions. However, the relative intensity between these peaks varies considerably due to the variation of the co-dopant/compensator (Li+, Na+, K+) concentration, representing the variation of the crystal field. Effects of different charge compensators (A+) and their concentration on the structural and luminescence properties of ZrO2:(0.01)Dy3+:xA+ phosphors were thoroughly investigated. Further, Judd-Ofelt parameters were calculated. Total emission colour (TEC) concentration of ZrO2:(0.01)Dy3+ phosphors were improved remarkably with the addition of charge compensators (A+), which would promote their applications in solid state lighting. The effective blue emission of the phosphors was changing with different co-dopant incorporation. Implying possible use of this material as a blue emitting phosphor as a blue emitting component in three-component white light-emitting diodes (WLEDs).

The emergence and prospects of carbon dots with solid-state photoluminescence for light-emitting diodes.

The significant features of carbon dots (CDs), such as bright and tunable photoluminescence, high thermal stability, and low toxicity, endow them with tremendous potential for application in next generation optoelectronics. Despite great progress achieved in the design of high-performance CDs so far, the practical applications in solid-state lighting and displays have been retarded by the aggregation-caused quenching (ACQ) effect ascribed to direct π-π interactions. This review provides a comprehensive overview of the recent progress made in solid-state CD emitters, including their synthesis, optical properties and applications in light-emitting diodes (LEDs). Their triplet-excited-state-involved properties, as well as their recent advances in phosphor-converted LEDs and electroluminescent LEDs, are mainly reviewed here. Finally, the prospects and challenges of solid-state CD-based LEDs are discussed with an eye on future development. We hope that this review will provide critical insights to inspire new exciting discoveries on solid-state CDs from both fundamental and practical standpoints so that the realization of their potential in optoelectronic areas can be facilitated.

Synergistic interaction of multi-functional additives at the buried interface for efficient blue perovskite light-emitting diodes

The synergistic effect of the doping strategy of basic amino acid salts at the interface enables the simultaneous modification of PEDOT:PSS and the bottom interface of the perovskite film to achieve efficient sky-blue PeLEDs.