Warm White Light-emitting Diodes Research Articles

Synthesis and photoluminescence of Ba1-xSrxMgSi4O10:Eu2+ phosphors for warm white light-emitting-diodes

Efficient and thermally stable blue-cyan-emitting phosphors are urgently demanded to cover the “cyan gap” for high quality light-emitting-diodes (LEDs) lighting. This work provides a series of blue to cyan color-tunable Ba0.96-xSrxMgSi4O10:0.04Eu2+ phosphors developed via solid-solution method. The phase transformation, photoluminescence, quantum efficiency and thermal stability were investigated in detail. Notably, Sr2+ substitution is effective to red-shift the emission toward cyan emission (from 465 to 480 nm). Simultaneously, the quantum efficiency and thermal stability can be well maintained. Finally, using a 365 nm near-ultraviolet (NUV) LED chip combining with the as-prepared blue-cyan-emitting phosphor, β-SiAlON:Eu2+ green-emitting phosphor and CaAlSiN3:Eu2+ red-emitting phosphor, a warm-white LED device was fabricated with correlated color temperature (CCT) of 4329 K, and color-rendering index (CRI) of 92. These results indicate that the Ba1-xSrxMgSi4O10:Eu2+ blue-cyan-emitting phosphors may have potential applications for high quality NUV-pumped warm-white LED lighting.

Controllable morphology, excellent stability and non-equivalent doping-induced optical properties of Mn4+-activated K2NaScF6 red phosphor for high-quality warm WLED

Currently, Mn4+ activated fluoride red phosphor has been widely studied to improve the optical performance of white light-emitting diode (WLED) in the field of high-efficiency lighting and wide color gamut backlight display. In this paper, a series of red-emitting K2NaScF6:Mn4+ phosphors are synthesized by a simple co-precipitation method with a non-equivalent substitution of Mn4+ for Sc3+ at room temperature. The crystal structure, morphology and elemental composition of K2NaScF6:Mn4+ phosphors prepared using different reaction conditions are systematically investigated. Interestingly, the K2NaScF6:Mn4+ phosphors exhibit narrowband red emission with low correlated color temperature (CCT), high color purity and short fluorescence lifetime. Compared to equivalent doping, the mechanism of short fluorescence lifetime caused by non-equivalent doping has also been systematically discussed. The optimal doping concentration is determined by setting a series of Mn4+ doping concentrations and the concentration quenching mechanism is analyzed. The crystal field strength (Dq), Racah parameters (B and C) and nephelauxetic ratio (β1) are calculated in detail to evaluate the crystal field environment of Mn4+ in K2NaScF6. The good water resistance of the as-prepared sample K2NaScF6:Mn4+ is verified by comparing with the commercially available phosphor K2SiF6:Mn4+. Moreover, the thermal stability is also analyzed by calculating the activation energy (Ea), chromaticity shift (ΔE) and chromaticity coordinate variation (CCV). Importantly, the as-packaged warm WLED (InGaN chip + YAG:Ce3+ + K2NaScF6:Mn4+) has excellent optical properties (CCT = 4082 K, color rendering index (CRI, Ra = 91.2) and luminous efficiency (LE) = 78.86 lm/W), and it exhibits good output stability at high drive currents. In summary, our work demonstrates that K2NaScF6:Mn4+ red phosphors possess a great potential application in warm WLED for the indoor lighting.

Novel self-activated red-emitting CsSrEu (PO3)6 phosphor: Synthesis, luminescent properties and enhancement by partially anion substitution

Novel self-activated red-emitting CsSrEu(PO3)6 was synthesized by high-temperature solid-phase method, and their enhanced luminescence were obtained by the modification of local structure. CsSrEu(PO3)6 was efficiently excited at 394 nm and emitted bright red light centered around 609 nm. Their luminescence intensity of CsSrEu(PO3)6 phosphor substituted by (BO3)3-/(SiO4)4- is about 1.346 or 1.454 times of the initial values respectively. The temperature-dependent luminescent spectra show that the emission intensity of CsSrEu(PO3)6 substituted by (BO3)3-/(SiO4)4- at 423 K remains 90.9 % and 86.6 % of the initial value respectively. The internal quantum efficiency is 88.4 % and 83.5 % respectively. White light-emitting diode fabricated by the phosphors, commercial blue-green phosphors and 395 nm chips show high color quality. The overall results indicate that the CsSrEu(PO3)6 phosphor substituted by (BO3)3-/(SiO4)4- group is promising candidate in warm white LED and anionic group substitution can be used to optimize luminescent properties of phosphors.

Substrate and nutrient manipulation during continuous cultivation of extremophilic algae, Galdieria spp. RTK 37.1, substantially impacts biomass productivity and composition.

The extremophilic nature and metabolic flexibility of Galdieria spp. highlights their potential for biotechnological application. However, limited research into continuous cultivation of Galdieria spp. has slowed progress towards the commercialization of these algae. The objective of this research was to investigate biomass productivity and growth yields during continuous photoautotrophic, mixotrophic and heterotrophic cultivation of Galdieria sp. RTK371; a strain recently isolated from within the Taupō Volcanic Zone in Aotearoa-New Zealand. Results indicate Galdieria sp. RTK371 grows optimally at pH 2.5 under warm white LED illumination. Photosynthetic O2 production was dependent on lighting intensity with a maximal value of (133.5 ± 12.1 nmol O2 mgbiomass -1 h-1) achieved under 100 μmol m-2 s-1 illumination. O2 production rates slowed significantly to 42 ± 1 and <0.01 nmol O2 mgbiomass -1 h-1 during mixotrophic and heterotrophic growth regimes respectively. Stable, long-term chemostat growth of Galdieria sp. RTK371 was achieved during photoautotrophic, mixotrophic and heterotrophic growth regimes. During periods of ammonium limitation, Galdieria sp. RTK371 increased its intracellular carbohydrate content (up to 37% w/w). In contrast, biomass grown in ammonium excess was composed of up to 65% protein (w/w). Results from this study demonstrate that the growth of Galdieria sp. RTK371 can be manipulated during continuous cultivation to obtain desired biomass and product yields over long cultivation periods.

Highly effective red phosphor for warm white LEDs without rare earth elements

The use of red fluorescent powder derived from nitrides and oxides in warm white LEDs is a pressing concern due to its lower quantum efficiency. Fluoride red phosphors activated by Mn4+ ions show promising potential for application in white light-emitting diodes (LEDs) due to their distinctive narrowband red emission and broad blue excitation, along with the relatively mild synthesis conditions required. However, the quantum efficiency of early Mn4+-doped fluoride phosphors was not optimal, highlighting the importance of identifying a suitable preparation method and matrix. Here, we introduce an efficient and thermally stable red fluoride phosphor, Cs2SiF6:Mn4+, which demonstrates a remarkable quantum efficiency of 98.32 % achieved through ion exchange techniques. However, even at a temperature of 423 K, the luminous intensity still maintained at 95 % of that under room temperature conditions. By incorporating Cs2SiF6:Mn4+ as a red emitter, a stable 10 W high-power warm white LEDs with a luminous efficiency of approximately 126.1 lm/W can be realized. These findings underscore the significant potential of the red phosphor Cs2SiF6:Mn4+ in advancing high-performance, high-power warm white LEDs.

Development and Evaluation of a High-Efficacy Solar-Powered Light Trap for Rice Black Bug (Scotinophara Coartata) Management

Rice black bugs (RBB) are a major pest causing significant yield losses in rice farms. This study investigates a novel solar-powered light trap for RBB control. The trap utilizes LEDs with different color temperatures (warm white and daylight) and incorporates an auto-response system for efficient operation. Performance evaluation over three months revealed the highest efficacy for the 50-watt warm white LED bulb (948 grams captured), followed by the daylight bulb (724 grams). However, the study found no significant difference between developing light traps with warm white and daylight LED in capturing RBBs. The trap's functionality was excellent, with low maintenance requirements. These findings suggest that the solar-powered light trap with warm white LEDs offers a promising, sustainable solution for RBB management in rice production.

Phosphor Ceramic Composite for Tunable Warm White Light.

Composite phosphor ceramics for warm white LED lighting were fabricated with K2SiF6:Mn4+ (KSF) as both a narrowband red phosphor and a translucent matrix in which yellow-emitting Y3Al5O12:Ce3+ (YAG) particles were dispersed. The emission spectra of these composites under blue LED excitation were studied as a function of YAG loading and thickness. Warm white light with a color temperature of 2716 K, a high CRI of 92.6, and an R9 of 77.6 was achieved. A modest improvement in the thermal conductivity of the KSF ceramic of up to 9% was observed with the addition of YAG particles. In addition, a simple model was developed for predicting the emission spectra based on several parameters of the composite ceramics and validated with the experimental results. The emission spectrum can be tuned by varying the dopant concentrations, thickness, YAG loading, and YAG particle size. This work demonstrates the utility of KSF/YAG composite phosphor ceramics as a means of producing warm white light, which are potentially suitable for higher-drive applications due to their increased thermal conductivity and reduced droop compared with silicone-dispersed phosphor powders.

A comparative study on the impact of cation replacements on the structural, optoelectronic and thermodynamic characteristics of hexafluorides red phosphors Cs2MF6 (M = C, Ge, Pb, Si) using first-principles calculations: a prospect for warm-white LEDs (w-LEDs) applications

A comparative study on the impact of cation replacements on the structural, optoelectronic and thermodynamic characteristics of hexafluorides red phosphors Cs2MF6 (M = C, Ge, Pb, Si) using first-principles calculations: a prospect for warm-white LEDs (w-LEDs) applications

Efficacy and Optimal Timing of Warm-white or Red + Far-red LED Lamps in Regulation of Flowering in Long-day Ornamentals

When natural days are short, photoperiodic lighting at the end or beginning of the day (day extension) or in the middle of the night (night break) promotes flowering of long-day plants. The objective of this study was to compare broad-spectrum warm-white light-emitting diodes (LEDs) and red (R) + far-red (FR) LEDs at flowering regulation when delivered at different timings in the night period. We performed a greenhouse experiment on four long-day ornamentals [coreopsis (Coreopsis grandiflora) ‘Early Sunrise’, snapdragon (Antirrhinum majus) ‘Liberty Classic Yellow’, petunia (Petunia ×hybrida) ‘Easy Wave Burgundy Star’, and petunia ‘Wave Purple Improved’]. We grew plants under a truncated 8-hour photoperiod with or without low-intensity (∼2 μmol·m−2·s−1) nighttime lighting from warm-white or R+FR LEDs. For each light quality, we delivered four timings: 1) 8 hours after dusk; 2) 8 hours before dawn; 3) 4 hours after dusk + 4 hours before dawn; and 4) 4-hour night break. The effectiveness of floral promotion was determined by time from the treatment onset to the first open flower. Coreopsis flowered similarly under all lighting treatments, irrespective of light quality and timing, but did not flower under the short-day treatment by the end of the experiment. At flowering, coreopsis was 18% to 19% shorter under white than R+FR LEDs. In contrast, snapdragon flowered 9 to 20 days later under white than R+FR LEDs, when delivered for 8 hours at night, but flowered similarly under these two lamp types as a 4-hour night break. Compared with the short-day treatment, white and R+FR LEDs promoted flowering of both petunia cultivars, although flowering generally occurred later under white than R+FR LEDs. Snapdragon and petunia ‘Easy Wave Burgundy Star’ developed 30% to 122% more lateral branches under white than R+FR LEDs, when delivered for 8 hours at night. The effectiveness of warm-white LEDs was generally unaffected by timing, although it was most promotive of flowering in snapdragon when delivered for 8 hours before dawn. For R+FR LEDs, 8-hour day-extension lighting was generally more effective than 4-hour night-break lighting, irrespective of timing. We conclude when delivered for 8 hours at night, warm-white LEDs are generally less effective than R+FR LEDs at promoting flowering of long-day ornamentals but similarly effective as 4-hour night-break lighting. The effectiveness of day-extension lighting is generally independent of timing, although for R+FR LEDs, 8 hours after-dusk and/or before-dawn lighting was generally more effective than 4-hour night-break lighting.

Effectively enhanced the luminescent properties and water resistance of K2TaF7: Mn4+ red phosphors by introducing In3+ ions in the matrix and constructing a homogeneous core-shell structure

Shell-free K2Ta1-xInxF7: Mn4+ red phosphor was synthesized by introducing In3+ ions in K2TaF7: Mn4+ with a non-centrosymmetric octahedral structure. The strategy of the heterogeneous substitution of In3+ by Ta5+ further distorted the octahedral structure, effectively enhanced the emission intensity of Mn4+. Its overall luminous intensity was increased to 6.9 times that of K2TaF7: Mn4+. Moreover, the red phosphor with a homogeneous core-shell structure was successfully prepared by using a weak reducing agent citric acid to solve the problem of poor water resistance. After soaking in water for 10 days, the emission intensity of the red phosphor with a homogeneous core-shell structure retained 90% of the initial value. It is the first time to successfully construct a core-shell structure for A2BF7: Mn4+ type fluoride phosphors to effectively improve its water resistance. Mixing it with commercial YAG: Ce3+ yellow phosphor and encapsulating them with a commercial blue chip led to the development of warm white light-emitting diodes (WLEDs) with good qualities. K2Ta1-xInxF7: Mn4+ red phosphor with homogeneous core shell is a novel red phosphor with good luminous performances and excellent water resistance.

Highly efficient blue-light-excitable ultra-broadband orange-emitting Mg2.5Y1.5Al1.5Si2.5O12:Ce3+ garnet phosphors for solid-state lighting

Lighting and display technologies are revolutionized by the invention of YAG:Ce3+ phosphors driven by InGaN blue light-emitting diode (LED). Yet, the faint emission components in the red spectral region from typical LED devices can cause circadian rhythm disorders and aesthetic fatigue of the human eye. Developing broadband orange-emitting phosphor with abundant red coverage is one of the approaches for addressing this challenging problem. Herein, an innovative ultra-broadband orange-emitting Mg2.5Y1.5Al1.5Si2.5O12:Ce3+ (MYASO:Ce3+) garnet phosphor is successfully reported to bridge the above gap. The representative MYASO:4%Ce3+ sample exhibits an unexpectedly luminescence band with the full width at half maximum (FWHM) of up to 155 nm, the high thermal robustness (58%@423 K), and satisfactory internal quantum efficiency of 67% upon 465 nm blue light excitation. Such a large FWHM value results from the occupation of a single crystallographic site of Ce3+ in the dodecahedral [YO8] position of MYASO garnet host. Red-shift emission with respect to commercial YAG:Ce3+ is mainly attributed to the cooperative effect of the enhanced crystal field strength and increased Stokes shift. The emission intensity reduction at the high-temperature environment of MYASO:4%Ce3+ is derived from the enhancement of the thermal cross-relaxation associated with the larger Stokes shift (4839 cm−1). The resulting high-quality warm white LED device fabricated from the optimal MYASO:4%Ce3+ sample shows a satisfactory color rendering index (CRI = 84), comfortable correlated color temperature (CCT = 4032 K) and an excellent luminous efficacy (LE = 58.7 lm W−1) under a 60 mA drive current. These findings stimulate the exploration of ultra-broadband orange-emitting phosphors with abundant red emission to fabricate high-CRI warm-white LEDs for healthy solid-state lighting.

Spectral studies of thermally stable Dy3+/Sm3+ co-doped Li2Ba5W3O15 phosphors for warm white LEDs

In the current study, a series of Li2Ba5W3O15: RE3+ (RE = Dy, Sm) [LBW:Dy3+/Sm3+] phosphors were prepared using a high-temperature solid-state method. X-ray diffraction, Scanning electron microscopy with energy-dispersive x-ray analysis scans showed that the crystal form was consistent with the standard LBW and comprised small irregularly shaped particles. Diffuse reflectance spectral (DRS) data was utilized to calculate the band gaps. Fluorescence study shows that LBW material doped with Dy3+ and Sm3+ yield distinct colors at 496 nm (blue) for Dy3+ and 582 nm (green-yellow), 612 nm (yellow), and 669 nm (red) for Sm3+ when excited by near-ultraviolet (336 nm) light. The observation of energy transfer between Dy3+ and Sm3+ ions play a role in modifying the luminescence of LBW:Dy3+/Sm3+ co-doped phosphors. With a constant excitation wavelength (λ Ex), different levels of activator doping lead to a change in the emission colors from their neutral white light to a deep orange-red region for LBW:Dy3+/Sm3+ phosphors. The decay curves demonstrate a decrease in lifetime with an increase in the concentration of activator ions (Sm3+). For D3S5 phosphor, the temperature-dependent photoluminescence characteristics were analyzed under λ Ex = 336 nm excitation. The results indicate excellent luminescence thermal stability with an activation energy of 0.16 eV at λ Ex = 336 nm. With its low color-correlated temperature and good thermal stability, the prepared phosphor sample shows potential as a solid-state emitting phosphor that can be used with UV chip stimulation for warm white LED applications.

Er3+-activated Na0.5La0.5MoO4 multifunctional molybdate phosphors for optical thermometers and white LEDs

In this report, we have successfully prepared a series of Er3+-activated Na0.5La0.5MoO4 green molybdate phosphors by solid-state reaction. The X-Ray diffraction patterns confirmed that all diffraction peaks of Na0.5La0.5MoO4:Er3+ phosphors matched well with the standard data card with orthorhombic phase and the Rietveld refinement results indicated that the space group of the crystal structure was I41/a. Under 379 nm excitation, Na0.5La0.5MoO4:3%Er3+ phosphor exhibited strong green emission, with two strong emission peaks at 530 nm, 551 nm and a weak one centered at 656 nm, corresponding to the transitions of 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2, respectively. The experimental results showed that the optimal doping concentration of Er3+ was x = 3%, and electric dipole-dipole interaction was the major mechanism for the concentration quenching according to Dexter theory. Surprisingly, the optimal Na0.5La0.5MoO4:3%Er3+ phosphor presented thermal enhancement to the ratio of 2H11/2 → 4I15/2 transition to 4S3/2 → 4I15/2 transition in the elevated temperature range of 300–475 K. The maximum Sa and Sr were 1.79 × 10−2 K−1 and 1.094% K−1 respectively, which were applied to optical thermometers based on fluorescence-intensity-ratio technique. Furthermore, Na0.5La0.5MoO4:3%Er3+ phosphor had excellent thermal quenching performance (I425K/I300K = 93.47%) and high activation energy (Ea = 0.366 eV). Finally, the prepared Na0.5La0.5MoO4:3%Er3+ green phosphor, commercial BaMgAl10O17:Eu2+ blue phosphor and CaAlSiN3:Eu2+ red phosphor were combined with the 365 nm near-UV chip to produce a warm white LED device with high color index (Ra = 86.4) and low correlation color temperature (CCT = 4328 K). The above results suggested that the Er3+-activated Na0.5La0.5MoO4 multifunctional phosphors had considerable potential in the field of optical temperature measurement and phosphor-converted white light emitting diodes.

Tuning of emission in BaLa1−x−yGa3O7:xDy3+, yEu3+ by local symmetry effects for WLEDs

Melilite structured phosphor is a significant luminescent material, but limited by its structure and luminescent properties, its luminescence intensity and spectral composition cannot satisfy the application requirements. To solve this issue, we look into the connection for the first time between the amount of rare-earth elements added and the symmetry of structure in melilite phosphors. We got the results by looking at the PL spectral data and J-O parameters of the melilite phosphor BaLa1−x−yGa3O7:xDy3+,yEu3+. Dy3+ was located in the low symmetry site, resulting in the local asymmetry being successfully enhanced to obtain warm-white color coordinates (0.398, 0.393) by adjusting the concentration of Eu3+ to vary the Y/B ratio of Dy3+ and the R/O ratio of Eu3+. Meanwhile, in the way that energy is transferred with an electric quadrupole-electric quadrupole between phosphor dopant ions. The energy transfer efficiency of Dy3+-Eu3+ is up to 81.99 %. At 475 K, the phosphor maintains an intensity of 81.1 % and exhibits reliable thermal stability. The color purity and EQE of BLGO:0.40Eu3+ are 49.7 % and 38.56 %, respectively. These results reveal that modifying the local symmetry surrounding the doped ions allows for adjusting the luminescence's wavelength composition. This approach can be applied to phosphors generated for warm white light-emitting diodes (WLEDs) with a single matrix.

Efficient preparation strategy of high quantum yield multicolor CDs for warm white LED

Multicolor carbon dots (CDs) possess tremendous potential applications, especially in optoelectronic devices. However, further applications in warm white LED have been constrained due to the extremely low quantum yield (QY) of multicolor CDs. In this work, fluorescence enhancement multicolor CDs (o-CDs(cat.) (emitted yellow, Em = 550 nm, QY = 85.4 %), m-CDs(cat.) (emitted blue, Em = 440 nm, QY = 35.7 %), p-CDs(cat.) (emitted red, Em = 610 nm, QY = 73.8 %)) with almost 15 % QY improvement, without changing the fluorescence emission wavelength, was successfully achieved by introducing MnSO4 into the reaction system. The relevant mechanism may be the catalytic effect of MnSO4, which leads to the increased content of C = N and pyridine N, further suppressing non radiative transitions, leading to the increasement of QY. Finally, the obtained high QY multicolor CDs were applied to warm white LED with the color coordinates (CIE) of (0.33,0.36), color rendering index (CRI) of 90, correlated color temperature (CCT) of 3473 K. Laying the foundation for the research methods and mechanisms of metal ion caused high QY of CDs.

STUDY OF K2SiF6:Mn4+@SiO2 PHOSPHOR FOR WHITE LEDS WITH HIGH ANGULAR COLOR UNIFORMITY

The distinctive wide-band blue illumination absorption and red strait-line discharge of the phosphor K2SiF6:Mn4+ (KMnSF) make it an attractive material for manufacturing warm white light-emitting diodes (WLED). Nevertheless, using the highly corrosive raw ingredient HF to produce commercial KMnSF red phosphor has negative effects on the environment and people. In this study, microfluidic technology was used to successfully manufacture the KMnSF without the need for HF compound while resulting in a phosphor product with homogenous granule shape and size. The luminescence capabilities of the KMnSF samples were then thoroughly examined and characterized. Eventually, we made WLED packages comprising of blue LED chips, yellow phosphor Y3Al5O12:Ce3+ (YGA:Ce), red phosphor KMnSF, and SiO2 scattering particle. Via varying the SiO2 concentration during the simulation process, the prepared WLED’s optical performances are obtained. The scattering properties of the phosphor layer as well as the lighting transmission and distribution were simulated with the utilization of both LightTools software and Monte Carlo theory. According to the outcomes, the microfluidic-synthesized K2SiF6:Mn4+ proves to be appropriate for WLED apparatuses. Besides, the proposed phosphor compound with SiO2 scattering particles showed the improvement in luminous flux and angular uniformity of the WLED.

The effect of different light wavelengths on the germination of lettuce, cabbage, spinach and arugula seeds in a controlled environment chamber

The rapid development of vertical farming techniques in recent years has accelerated the necessity for a more thorough investigation into the utilization of artificial lighting. Cultivation in controlled environment systems primarily relies on artificial lighting to provide energy to the plants. One food category that has surged in popularity in recent years is microgreens, which are seedlings consumed during their early stages of growth. Hence, enhancing seed germination and promoting rapid seedling growth can yield significant benefits in this field. The main aim of this study was to analyze how lettuce, cabbage, spinach, and arugula seeds respond under various light spectra and photoperiodic schemes. The selected spectra were UV-A, blue, red, far-red, blue+red, blue+red+far-red, cool-white LED, warm-white LED and darkness, under three different photoperiods: 4, 12 and 24 h. All lighting treatments presented different effects on both seed germination and the morphological characteristics of the seedlings. Lettuce and spinach seeds exhibited robust germination capacity in both darkness and light. However, significant increases in germination rates were observed for cabbage and arugula when exposed to light. In the case of lettuce, a 12 h photoperiod with a blue spectrum led to a 100% germination rate and a leaf area of 77.4 mm². For cabbage, the highest germination rate observed was 70%, which occurred under a blue-red spectrum with a 12 h light cycle. The corresponding leaf area was 44 mm². Spinach exhibited its highest leaf area, reaching 119.16 mm², and a 90% germination rate when exposed to a four h far-red spectrum. Arugula achieved its greatest leaf area, measuring 58.57 mm², and a germination rate of 70% when exposed to a 24 h photoperiod combined with blue-red-far-red lighting. The proper combination of spectra can significantly enhance seed germination rates and guide the plants’ growth towards the desired morphological characteristics.

A new yellowish‐green‐emitting phosphor: Eu2+‐doped Ba3YAl2O7.5

AbstractA yellowish‐green emitting phosphor Ba3YAl2O7.5:Eu2+ was synthesized by a solid‐state method. The crystal structure, luminescence, concentration quenching, fluorescence decay, and thermal quenching properties were systematically investigated. Under blue light (440 nm) excitation, Ba3YAl2O7.5:Eu2+ phosphors exhibit a yellowish‐green emission peaking at 550 nm with a full width at half maximum ∼ 69 nm, and The Commission Internationale de l'Eclairage (CIE) coordinates of Ba3YAl2O7.5:Eu2+ are (0.4064, 0.5811). Structural analysis and Van Uitert equation along with fluorescence lifetime analysis reveal that Eu2+ ions occupy 6‐coordinated Y and 9‐coordinated Ba sites in Ba3YAl2O7.5, and therefore generate two emission sub‐bands at 582 and 548 nm. In addition, Ba3YAl2O7.5:Eu2+ phosphor remaining 43% photoluminescence emission intensity at 125°C with an activation energy of 0.372 eV. Utilizing the title phosphor (Ba3YAl2O7.5:3%Eu2+), commercial red (Ca,Sr)AlSiN3:Eu2+ (CSAlSi:Eu2+) phosphor, and InGaN‐based blue light emitting diode (LED) chip, a proof‐of‐concept warm white LEDs (WLEDs) with a color rendering index of 80.1, CIE chromaticity coordinates of (0.411, 0.381), luminous efficacy of ∼ 22.13 lm/W, and correlated color temperature of ∼ 3288 K is achieved. Thus, Eu2+ activated Ba3YAl2O7.5 phosphors have the potential application in WLEDs pumped by a blue LED chip for solid‐state lighting application.

Ce3+-Activated SrLu2Al3ScSiO12 Cyan-Green-Emitting Garnet-Structured Inorganic Phosphor Materials toward Application in Blue-Chip-Based Phosphor-Converted Solid-State White Lighting.

Phosphor-converted white-light-emitting diodes (WLEDs) with superhigh color rendering index (CRI) are the ongoing pursuit of next-generation solid-state lighting. One of the most important challenges is the limited improvement in CRI on account of the absence of a cyan component in the typical commercial combination. Here, a bright broad-band cyan-green-emitting phosphor with cubic garnet structure, SrLu2Al3ScSiO12:Ce3+ (SLASSO:Ce3+), was successfully reported, which can compensate for the absence of cyan cavity in the 480-520 nm blue-green emission region. With 439 nm blue-light irradiation, the as-fabricated SLASSO:Ce3+ phosphor yields a broad-band cyan-green emission with the maximum emission peak positioned at 525 nm and an appropriate full width at half-maximum (fwhm) of 111 nm, capable of providing more cyan emission component without sacrificing green emission. Meanwhile, the optimal SLASSO:2%Ce3+ phosphor features CIE color coordinates of (0.3254, 0.5470) with cyan-green hue, along with a high internal quantum efficiency of up to 93%. Additionally, thermal stability measurements at different temperatures reveal that the luminescence emission intensity of the proposed phosphor retains 44% of its original integral emission intensity at 423 K with respect to room temperature, while also demonstrating an excellent color stability (ΔE = 5.4 × 10-3). This work shows that the highly efficient SLASSO:Ce3+ garnet phosphor can be utilized as a potential cyan-green-emitting phosphor for filling the cyan gap, resulting in the construction of a high-quality warm WLED with high CRI for "human-centric" sunlight-like full-spectrum solid-state illumination.

Multiwavelength Excitation in Ho3+-Doped All-Inorganic Double Perovskites Achieved by Codoping Mn2+ for Warm-White LEDs and Plant Growth.

Doping lanthanide ions is an efficient method to modify the optical properties of lead-free double-perovskite halides. However, most lanthanide-doped double perovskites show a low luminescence efficiency and require a high excitation energy. Here, we have successfully prepared a series of Ho3+-doped Cs2NaBiCl6 microcrystals through a simple hydrothermal method and obtained strong characteristic emissions of Ho3+ at 492 and 657 nm under low-energy excitation (449 nm). After codoping Mn2+, apart from the characteristic emissions from Ho3+ under 450 nm wavelength excitation, the orangish-red luminescence consisting of the emission band centered at 591 nm from Mn2+ and a sharp emission peak at 657 nm from Ho3+ is obtained under 355 nm UV light excitation. Photoluminescence (PL) emission and excitation spectra, along with the PL decay curves, confirm the existence of an energy-transfer channel from Cs2NaBiCl6 to Mn2+ and then from Mn2+ to Ho3+. The enhanced absorption efficiency (10.5 → 70.7%) suggests that the codoping of Mn2+ overcomes the low absorption efficiency caused by f-f forbidden transitions of Ho3+. Finally, the diverse luminescent performance within the Cs2NaBiCl6:Ho3+, Mn2+ phosphor is realized by altering the excitation wavelength, thereby enabling its application in warm-white-light-emitting diodes and plant growth in this work.