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(Ba1−xSrx)0.98Eu0.02ScO2F produces a tunable emission from cyan to green upon Sr2+ substitution. Ab initio molecular dynamics simulations revealed that Sr2+ weakens the local rigidity lowering the efficiency and thermal stability of the phosphors.

Monitors, televisions, and smartphones have been revolutionized by the invention of InGaN-based LED backlighting. Yet, regular exposure to the bright blue light emitted by these screens can lead to mood disorders and insomnia. Switching to a "human-centric" display that uses a violet-emitting LED chip and a trichromatic phosphor blend is one materials chemistry solution for this problem. The challenge is finding a blue-emitting phosphor with a sufficiently small Stokes’ shift to down-convert the violet LED light. This study reports a new oxynitride phosphor that meets this need. K3AlP3O9N:Eu2+ exhibits a narrow (45 nm, 2206 cm-1), thermally robust, and efficient blue photoluminescence upon violet excitation. Computational modeling and photoluminescence spectroscopy revealed that a rare combination of preferential excitation and site-selective quenching produce the desired optical properties. Combining K3AlP3O9N:Eu2+ with red- and green-emitting phosphors and a violet LED covers 10% more of the color gamut than a commercial tablet while simultaneously mitigating blue light exposure en route to next-generation, human-centric displays.

Single crystals of three new compounds, Na

The proliferation of energy-efficient light-emitting diode (LED) lighting has resulted in continued exposure to blue light, which has been linked to cataract formation, circadian disruption, and mood disorders. Blue light can be readily minimized in pursuit of "human-centric" lighting using a violet LED chip (λem ≈ 405 nm) downconverted by red, green, and blue-emitting phosphors. However, few phosphors efficiently convert violet light to blue light. This work reports a new phosphor that meets this demand. Na2MgPO4F:Eu2+ can be excited by a violet LED yielding an efficient, bright blue emission. The material also shows zero thermal quenching and has outstanding chromatic stability. The chemical robustness of the phosphor was also confirmed through prolonged exposure to water and high temperatures. A prototype device using a 405 nm LED, Na2MgPO4F:Eu2+, and a green and red-emitting phosphor produces a warm white light with a higher color rendering index than a commercially purchased LED light bulb while significantly reducing the blue component. These results demonstrate the capability of Na2MgPO4F:Eu2+ as a next-generation phosphor capable of advancing human-centric lighting.

The host structure of the new phosphor Sr6(BO3)3BN2:Eu2+ crystallizes tetragonally (Sr6(BO3)3BN2, P42/mbc, Z = 8, a = 12.8173(3) A, b = 14.0740(5) A, Rint = 0.037, R1 = 0.052, and wR2 = 0.121) and ...

The dual emission produced from Mn2+ when codoped with rare earth ions like Eu2+ or Ce3+ in inorganic compounds makes these materials attractive as efficient, color-tunable phosphors for warm-white...

Phosphor-converted light emitting diodes (LEDs) are a highly efficient form of solid-state lighting. A key performance metric of a phosphor is its thermal quenching (TQ), which is the percentage lo...

Complex alkaline earth silicates have been extensively studied as rare-earth substituted phosphor hosts for use in solid-state lighting. One of the biggest challenges facing the development of new phosphors is understanding the relationship between the observed optical properties and the crystal structure. Fortunately, recent improvements in characterization techniques combined with advances in computational methodologies provide the research tools necessary to conduct a comprehensive analysis of these systems. In this work, a new Ce3+ substituted phosphor is developed using Ba5Si8O21 as the host crystal structure. The compound is evaluated using a combination of experimental and computational methods and shows Ba5Si8O21:Ce3+ adopts a monoclinic crystal structure that was confirmed through Rietveld refinement of high-resolution synchrotron powder X-ray diffraction data. Photoluminescence spectroscopy reveals a broad-band blue emission centered at ∼440 nm with an absolute quantum yield of ∼45% under ultraviolet light excitation (λex = 340 nm). This phosphor also shows a minimal chromaticity-drift but with moderate thermal quenching of the emission peak at elevated temperatures. The modest optical response of this phase is believed to stem from a combination of intrinsic structural complexity and the formation of defects because of the aliovalent rare-earth substitution. Finally, computational modeling provides essential insight into the site preference and energy level distribution of Ce3+ in this compound. These results highlight the importance of using experiment and computation in tandem to interpret the relationship between observed optical properties and the crystal structures of all rare-earth substituted complex phosphors.

In this paper, the photoluminescent properties of a lead-free double perovskite Cs2NaInCl6 doped with Sb3+ are explored. The host crystal structure is a cubic double perovskite with Fmm symmetry, a = 10.53344(4) A, and rock salt ordering of Na+ and In3+. It is a wide bandgap compound (Eg ≈ 5.1 eV), and substitution with Sb3+ leads to strong absorption in the UV due to localized 5s2 → 5s15p1 transitions on Sb3+ centers. Radiative relaxation back to the 5s2 ground state, via a 3P1 → 1S0 transition, leads to intense blue luminescence, centered at 445 nm, with a photoluminescent quantum yield of 79%. The Stokes shift of 0.94 eV is roughly 33% smaller than it is in the related vacancy ordered double perovskite Cs2SnCl6. The reduction in Stokes shift is likely due to a change in coordination number of Sb3+ from 6-coordinate in Cs2NaInCl6 to 5-coordinate in Cs2SnCl6. In addition to the high quantum yield, Cs2NaInCl6:Sb3+ exhibits excellent air/moisture stability and can be prepared from solution; these characteristics make it a promising blue phosphor for applications involving near-UV excitation.

The photoluminescence spectrum generated by an ordinary phosphor-converted white light-emitting diode (pc-wLED) that combines a blue LED chip with a yellow phosphor or a near-UV LED with red, green...

One of society’s grand challenges is to reduce energy usage in ways that are cost-effective, sustainable, and environmentally benign. Replacing incandescent and compact fluorescent light bulbs with...

In the race to develop new luminescent materials for the next generation of light-emitting-diode (LED)-based solid-state lighting and display applications, it is often forgotten that color theory and human perception should be some of the principal factors guiding materials design. In this Viewpoint, we explore some of the antiquated colorimetrics established originally for incandescent and fluorescent lighting and discuss how they are still widely applied in the literature today to interpret the color quality of luminescent materials, like inorganic phosphors and quantum dots, and to analyze prototype devices, despite their shortcomings. We then shift our analysis toward contemporary ideas in color theory that more accurately describe the color quality of modern LED light bulbs and flat-panel displays. Finally, the perspective examines the opportunities and challenges of applying these new concepts to guide the design of luminescent materials used in LED-based applications.

Downconverters, primarily inorganic phosphors, are critical components in white solid-state LED-based lighting and liquid crystal display backlights. Research efforts have led to a fundamental understanding of a downconverter's absorption, photoluminescence, and efficiency as a function of composition, structure, and processing conditions. However, considerably less work has focused on the reliability of phosphors once they are incorporated into LED packages. Solving these issues is often the final step before the commercialization of new materials, but the significant resources and time required to evaluate and mitigate materials failure are rarely discussed in the literature. In this Perspective, we discuss the need for conducting downconverter reliability testing and the potential of accelerating, screening, and understanding downconverter failure modes. Our focus highlights the mechanisms of failure and discusses how this influences materials selection and the design of different LED packages. We also stress the potential for accelerated reliability testing protocols and note the potential role first-principles calculations and data-driven models could play in establishing the compositional-processing trends for different aspects of downconverter reliability. We close with possible research directions that could improve downconverter reliability and emphasize the importance of assessing a material's (chemical) stability where multiple manufacturing and processing steps can dictate system performance.

The concept of human-centric lighting stems from the evolution of sunlight’s intensity and color temperature throughout the course of a day. This natural progression of bright cold-white light during the middle of the day to a softer warm-white light in the evening stimulates intrinsic photosensitive retinal ganglion cells that control our circadian rhythm. The blue-hue of daylight activates these cells to produce dopamine and cortisol while suppressing melatonin, the sleep hormone, to keep humans awake and alert. The current generation of energy-efficient LED lights reproduce daylight by converting a blue-emitting LED into a broad-spectrum white light using inorganic phosphors. Unfortunately, the resulting intense blue-hue generated by cheap LED bulbs and the underlying blue light from even the most expensive bulbs have been shown to cause macular degeneration, cataract formation, mood disorders, and circadian disruption, resulting in insomnia and fatigue. This talk will investigate the production of a ‘human-centric’ light that minimizes blue light by using a violet LED chip and inorganic phosphors. We report a new phosphor, Na2MgPO4F:Eu2+, which can be readily excited by violet light to produce a bright blue emission. This material possesses all the necessary requirements for LED lighting, including a high quantum yield, thermally robust emission, and impressive chemical stability. Incorporating this material into a prototype device demonstrates our ability produce a warm-white light with a higher color rendering index than a commercially purchased LED light bulb while significantly reducing the blue component.

The proliferation of energy-efficient light-emitting diode (LED) lighting has resulted in continued exposure to blue light, which has been linked to cataract formation, circadian disruption, and mood disorders. Blue light can be readily minimized in pursuit of "human-centric" lighting using a violet LED chip (λ

The dual emission produced from Mn

Complex alkaline earth silicates have been extensively studied as rare-earth substituted phosphor hosts for use in solid-state lighting. One of the biggest challenges facing the development of new phosphors is understanding the relationship between the observed optical properties and the crystal structure. Fortunately, recent improvements in characterization techniques combined with advances in computational methodologies provide the research tools necessary to conduct a comprehensive analysis of these systems. In this work, a new Ce

One of society's grand challenges is to reduce energy usage in ways that are cost-effective, sustainable, and environmentally benign. Replacing incandescent and compact fluorescent light bulbs with energy-efficient, solid-state white lighting is one of the easiest and most promising solutions. Eu

The production of white light based on a near-UV LED chip requires incorporating three inorganic phosphors that emit in the blue, green, and red portions of the visible spectrum. Using a near-UV LED has the advantage of generating a light with excellent color quality, but due to the large Stokes’ shift between the LED excitation and the multiple phosphor emissions, these devices can suffer from a low overall efficiency. To minimize this inherent energy loss, the three phosphors employed to convert the LED emission must be very efficient, as measured by the internal photoluminescent quantum yield (Φ). In this work, we report the synthesis of a cubic borate, Ba3Y2B6O15, which when substituted with Ce3+ becomes an efficient blue phosphor. This compound can be prepared using a multistep high temperature solid state synthesis with the ensuing photoluminescent measurements revealing a broad excitation band (300–415 nm) making this phosphor compatible with a 365 or 400 nm LED chip. Ba3Y2B6O15:Ce3+ luminesces bri...

Information on the 5d level centroid shift (ϵc) of rare-earth ions is critical for determining the chemical shift and the Coulomb repulsion parameter as well as predicting the luminescence and thermal response of rare-earth substituted inorganic phosphors. The magnitude of ϵc depends on the binding strength between the rare-earth ion and its coordinating ligands, which is difficult to quantify a priori and makes phosphor design particularly challenging. In this work, a tree-based ensemble learning algorithm employing extreme gradient boosting is trained to predict ϵc by analyzing the optical properties of 160 Ce3+ substituted inorganic phosphors. The experimentally measured ϵc of these compounds was featurized using the materials' relative permittivity (ϵr), average electronegativity, average polarizability, and local geometry. Because the number of reported ϵr values is limited, it was necessary to utilize a predicted relative permittivity (ϵr,SVR) obtained from a support vector regressor trained on data from ∼2800 density functional theory calculations. The remaining features were compiled from open-source databases and by analyzing the rare-earth coordination environment from each Crystallographic Information File. The resulting ensemble model could reliably estimate ϵc and provide insight into the optical properties of Ce3+-activated inorganic phosphors.

In the quest to predict photoluminescent efficiency in rare-earth substituted inorganic phosphors, research has shown that materials consisting of ordered, rigid crystal structures tend to possess the highest photoluminescent quantum yields. A compound's Debye temperature (ΘD), which can be calculated using ab initio calculations, is an ideal proxy for quantitatively comparing structural rigidity among different inorganic compounds, allowing potentially efficient phosphors to be selected from large crystal structure databases. However, the high computational cost of these calculations limits estimating ΘD for unsubstituted host crystal structures only. It is assumed that the low substitution concentration of the rare-earth luminescent center does not significantly influence a material's Debye temperature. This work evaluates the validity of this approximation by examining the effect of luminescent center substitution on a host structure's ΘD. Two well-known phosphors, (Y1–xCex)3Al5O12 (x = 0 − 0.05) and Ba1-δEuδMgAl10O17 (δ = 0 − 0.15), were synthesized with varying rare-earth concentrations, while ΘD was computationally estimated and then determined by ultrasonic pulse-echo speed-of-sound and low-temperature heat capacity measurements. The ensuing results provide key implications for using ΘD as a proxy for structural rigidity in substituted inorganic compounds.