Color Temperature Research Articles

Ca9-yMgyNaGd0.667(PO4)7:Eu2+: A Single Eu2+-Doped Full-Spectrum White Light Emission Phosphor with High Color Rendering Index.

The multi-cationic site occupation control of rare earth doped phosphor materials is one of the key factors in achieving single-phase full-spectrum emission. In this work, the site distribution of Eu2+ in Ca9NaGd0.667(PO4)7 (CNGP):x%Eu2+ phosphors with multi-cationic sites was determined. Under 385 nm excitation, CNGP:x%Eu2+ samples exhibited a cyan emission composed of three sub-Gaussian components. The CNGP:1.5%Eu2+ phosphor was structurally modified through the partial substitution of Mg2+ for Ca2+ according to the crystallographic site engineering theory, and corresponding luminescent properties had been adjusted. When the concentration of Mg2+ changed, the Ca9-yMgyNaGd0.667(PO4)7:1.5%Eu2+ (CNGPE:yMg2+) phosphors exhibited a tunable emission from cyan to orange and achieved white light emission at y = 0.6. Based on the change of the crystal field environment, the mechanism of Mg2+ substitution affecting the luminescence characteristics of CNGP:x%Eu2+ phosphors was researched in detail. The light-emitting diode device consisted of a CNGPE:0.6Mg2+ phosphor and a 385 nm chip and had a high color rendering index (CRI = 91.9), low correlated color temperature (CCT = 4852 K), and excellent color stability. The optical performance of this device makes it promising to be used in full spectrum lighting.

Bi3+ activated Li6Y(BO3)3 phosphors for full-spectrum lighting

The blue-violet emitting phosphors is a critical aspect of achieving a high-quality full-spectrum white light-emitting diodes (WLEDs). Here, the photoluminescence characteristics of blue-violet emitting phosphors Li6Y(BO3)3:Bi3+ and its application performances were systematically studied. The emission of the phosphors exhibits a high dependence on the excitation wavelength. Upon excitation at 372 nm, the phosphors emit blue light peaking at 407 nm. The excitation of 340 nm results in the occurrence of two peaks at 407 and 506 nm in emission spectra. A full-spectrum WLED prepared by coating a 365 nm n-UV LED and the mixture comprising the phosphors and three commercial phosphors. The WLED exhibits high color rendering index (Ra = 95) and low correlated color temperature (3555 K). Consequently, Li6Y(BO3)3:Bi3+ is a potential phosphor that can be used for full spectrum WLEDs.

The influence of lighting and thermal environments on sleep and cognitive function in older adults

Recent research has demonstrated the significant influence of lighting and thermal conditions on cognitive performance and sleep quality. However, a notable gap exists in understanding how these factors impact older adults within their living environments. This study examined the relationship between daily lighting and thermal exposures with cognitive performance and sleep quality in older adults. Eighteen older adults, with a mean age of 75 (SD = 7.7, female = 13), participated in a three-day study. Throughout the protocol, their indoor lighting and thermal conditions were monitored using environmental sensors. Participants were instructed to complete a series of cognitive tasks twice a day. Additionally, they wore a smartwatch-type actigraph and a wearable light tracker to monitor their sleep/wake patterns and daily light exposure. The findings showed that appropriate nighttime lighting correlated with improved evening cognitive performance. Higher nighttime indoor lighting intensity positively correlated with cognitive measures, while nighttime correlated color temperature (CCT) exposure had negative correlations. Daytime melanopic equivalent daylight illuminance (MEDI) exposure significantly predicted total sleep time, with increased circadian-effective light exposure reducing sleep fragmentation. Conversely, higher nighttime lighting intensity was linked to decreased sleep efficiency. Higher bedroom temperatures were associated with improved sleep efficiency and reduced fragmentation. These findings highlight the importance of optimizing lighting conditions and maintaining comfortable temperatures in residential environments to promote cognitive performance and sleep quality among older adults.

A new zero-dimensional hybrid antimony halide of (C25H46N)2SbCl5 with dual-emission and high quantum-efficiency for light-emitting application

Zero-dimensional (0D) organic-inorganic hybrid metal halides (OIHMHs) have received extensive attention due to their excellent photoelectric properties. Herein, a new 0D OIHMH single crystal, (C25H46N)2SbCl5, has been synthesized by slow antisolvent diffusion. In this crystal structure, C25H46N+ (C25H46N+ = Cetyldimethylbenzylammonium cations) cations separated SbCl52− to form a 0D square pyramid structure. (C25H46N)2SbCl5 single crystals (SCs) manifest bright orange-yellow dual-emission bands at 472 and 616 nm, while having a high photoluminescent quantum yield of 97.5 %. The lifetime of high energy (HE) emission and low energy (LE) emission at room temperature is 9.73 ns and 4.61 μs, respectively. Based on lifetime differences and temperature-dependent spectra, the HE emission band is ascribed to singlet self-trapped excitons (STEs), while the LE emission band with a broad full width at half maxima of 136 nm can be attributed to triplet STEs. (C25H46N)2SbCl5 appeared anti-thermal quenching behavior. In accordance with the luminescence characteristics of (C25H46N)2SbCl5, a warm white light-emitting diode device was fabricated with the correlated color temperature of 3410 K, the relevant color coordinate of (0.41, 0.39) and the color rendering index of 95.1, demonstrating (C25H46N)2SbCl5 a promising phosphor for solid-state light-emitting application.

High‐Efficiency Hybrid White Organic Light‐Emitting Diodes with Extremely Low Efficiency Roll‐Off and Superior Color Stability Enabled by an Emitting System with Imidazole‐Biphenyl Derivatives

AbstractHybride white organic light‐emitting diodes (WOLEDs) have experienced great success as a prospective technology for the new generation lighting source. Nevertheless, WOLEDs exhibiting excellent effciency and good color stability at high operation brightness are still rare. Herein, a simple but efficient blue molecule, pyrenoimidazole‐biphenyl (PPyIM), which exhibits promising external quantum efficiency (EQE) of 7.6% and 7.2% at the luminescence of 1000 −and 5000 cd m−2 in nondoped blue OLED, is first developed. And then, phenanthroimidazole‐biphenyl (PPIM) with analogous molecular skeleton of PPyIM is chosen as the host of phosphorescent dye PO‐01, and the resulting doped device achieves excellent EQE of 26.5% at the high luminescence of 5000 cd m−2. Furthermore, adopting PPyIM as nondoped blue emissive layer, the two‐color hybrid WOLED exhibites stable warm white emission with CIE coordinates of (0.454, 0.439), color rendering index (CRI) of 45, and correlated color temperature (CCT) of 2996 K. The maximum EQE reaches 23.5%, and the EQE still maintains 21.2% even at the luminance of 5000 cd m−2. Notably, this device exhibits exceptionally stable warm white emission, the CIE coordinates variation is only (0.004, 0.003) in the wide luminance range from 400 to 10000 cd m−2, representing the best outcome for hybrid WOLEDs to date.

Research on an Indoor Light Environment Comfort Evaluation Index Based on Electroencephalogram and Pupil Signals

With the development of modern technology, many people work for a long time around various artificial light sources and electronic equipment, causing them to feel discomfort in their eyes and even eye diseases. The industry currently lacks an objective quantitative environmental–visual comfort index that combines subjective and objective indicators. For this experiment, objective eye movement and electroencephalogram (EEG) signals were collected in combination with a subjective questionnaire survey and a preference inquiry for comprehensive data mining. Finally, the results on a Likert scale show that high screen brightness can reduce the visual fatigue of subjects under high illuminance and high correlated color temperature (CCT). Pupil data show that, under medium and high ambient illuminance, visual perception sensitivity is more likely to be stimulated, and visual fatigue is more likely to deepen. EEG data show that visual fatigue is related to illuminance and screen brightness. On this basis, this study proposes a new evaluation index, the visual comfort level (0.6404 average at a low screen brightness, 0.4218 average at a medium screen brightness, and 0.5139 average at a high screen brightness), where a higher score for the visual comfort level represents a better visual experience. The visual comfort level provides a useful reference for enhancing the processing of multi-dimensional and biomedical signals and protecting the eyes.

A novel Na2Ca2Si3O9: Tb3+ glass ceramic with high luminescence efficiency and robust thermal stability for white LED lighting application

Given the increasing demand for white light emitting diode (WLED) lighting devices marked by high color rendering indices (CRI) and exceptional thermal stability, there is a burgeoning interest in developing emitters with enhanced performance. Rare earth (RE) ion-activated glass ceramics (GCs) have garnered significant attention due to their outstanding physicochemical and thermal stability, alongside their high luminescence efficiency. In this study, the GCs doped with Tb3+ ions in the Na2O-CaO-SiO2 system matrix were synthesized, incorporating Na2Ca2Si3O9 nanocrystals averaging less than 100 nm in size. Notably, these GC materials demonstrated superior luminescence efficiency in the green light emission under the irradiation of 376 nm light compared to the parent glass. A comprehensive analysis of fluorescence spectra revealed an impressive internal quantum efficiency of 87.34 % for this Tb3+-doped GC. Furthermore, the GC retained 90 % and 84 % of the initial luminescence intensity at 150 °C and 200 °C in comparison to the luminescence level at room temperature, showcasing exceptional resistance to fluorescence thermal quenching. Verification experiments utilized UV LED chip, (Sr, Ca)AlSiN3: Eu2+ red phosphor, BaMgAl10O17: Eu2+ blue phosphor, and Tb3+-doped GC to encapsulate the WLED device, achieving a remarkable CRI of 92, CIE chromaticity coordinates (0.3547, 0.3361), and a correlated color temperature (CCT) of 4550K. In conclusion, the experimental outcomes unequivocally underscore the significant application potential of these Tb3+-doped GCs in the territory of warm WLED lighting.

Research on Characteristics Matching of Micro-LED Devices

This paper presents the design of a 40 × 40 micro-light-emitting (micro-LED) test array based on a 20 mm × 20 mm substrate. A study of the relationship between luminous brightness, driving current, and driving voltage revealed that the data voltages of the red, green, and blue micro-LED array from 0 to 255 grey levels are 0.31 V, 0.29 V, and 0.30 V, respectively, under the condition that the target brightness of the white field is 1000 nits and the color temperature is 9300 K. The brightness range of the red micro-LED array is 64.8–101.2%, the brightness range of the green micro-LED array is 66.5–102.8%, and the brightness range of the blue micro-LED array is 53.5–129.2%. In order to overcome the luminance nonuniformity, a grey level depth of 12 -bit is required. A 10T3C pixel driver circuit based on low-temperature polysilicon (LTPS) with a depth of 12 bits greyscale is designed and fabricated into the micro-LED display. A brightness uniformity of 84.1–97.1% can be achieved by brightness correction combined with a 12-bit greyscale depth system for micro-LED display. This provides a valuable reference point for subsequent improvements in the quality of micro-LED displays.

A phosphor-in-glass film prepared with a novel orange Lu2GdMg2AlSi2O12:Ce3+ phosphor and a cyan BaSi2O2N2:Eu2+ phosphor

The preparation of phosphor-in-glass (PiG) films containing orange and cyan phosphors is one of the possible ways to improve the color rendering index (CRI) and correlated color temperature (CCT) of white LEDs packaged with PiG films. Recently, by matrix ion substitution, we have synthesized a novel orange Lu2GdMg2AlSi2O12:Ce3+ phosphor. Then, we used a “coating and low-temperature sintering” method to prepare PiG films containing this novel orange phosphor and the commercial cyan BaSi2O2N2:Eu2+ phosphor on sapphire substrates. Combining these PiG films with blue LED chips, warm white LEDs with CRI above 90 and CCT below 4000 K can be obtained. This suggests that the PiG films containing cyan and orange phosphors are promising to improve the CCT and CRI of white LEDs packaged with PiG films.

A novel thermally-stable red phosphor CaYGaO4:Eu3+ for WLEDs and anti-counterfeiting ink

In this paper, CaYGaO4:xEu3+ (CYGO:xEu3+)phosphors were synthesized for the first time using a high-temperature solid-state method. The samples were characterized by X-ray diffractometer (XRD) and scanning electron microscope (SEM). Their energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to further investigate the microscopic composition of the samples. The forbidden bandwidths and densities of states of CYGO and CYGO:0.25Eu3+ were calculated by first principles methods. The emission and excitation spectra of the samples were tested by fluorescence spectroscopy, which showed that the samples can be excited by both UV and blue light. When the sample heated to 473 K, the luminescence intensity under 393 and 463 nm excitation stays at 83.99 % and 85.19 % of the room temperature, respectively, which demonstrates that CYGO:0.3Eu3+ possesses excellent thermal stability. The color coordinates (CIE), correlated color temperature (CCT) and color purity (CP) of the samples were also investigated. In order to explore its application in the field of white light-emitting diodes (WLEDs), CYGO:0.3Eu3+ was mixed with commercial blue and green phosphors in a certain ratio, and the chip was made into a WLED with 395 nm excitation, and the CIE of the lamps were (0.3338, 0.3521), with a correlated CCT of 5448 K, and a color rendering index (CRI) of Ra = 86.2. The thermal imaging performance of the small lamps was also evaluated for sustained usage, revealing minimal temperature fluctuations and excellent thermal stability. Consequently, CYGO:Eu3+ exhibits promising potential for applications in the field of WLEDs. Additionally, CYGO:0.3Eu3+ was selected as a representative sample for the creation of fluorescent ink and its subsequent application on various media. The outcomes indicate that this phosphor possesses promising potential for use in the field of anti-counterfeiting ink technology.

Near-pure red emission of highly thermally stable Eu3+ doped multi-component transparent oxyfluoride aluminosilicate glass-ceramic for red lasers and trichromatic WLEDs

In this paper, Eu3+ doped multi-component transparent aluminosilicate and oxyfluoride aluminosilicate glasses were fabricated by the melt-quenching procedure, and the glass-ceramics containing LiAlSi2O6 microcrystals (LAS glass-ceramics) were produced by a two-step heat treatment process. The XRD, SEM, and EDS data demonstrate that spherical single-phase LiAlSi2O6 microcrystals have precipitated from the glass matrices. The microhardness and flexural strength of the glass-ceramics vary in 6.27–6.66 GPa and 89.18–155.75 MPa, respectively. Phonon sideband analysis reveals that the phonon energies for both fluorine-containing and fluorine-free LAS glass-ceramics are approximately 971 cm−1, and the multiphonon relaxation rates (Wmp/W0) of the former are lower than those of the latter. Given its lower Wmp/W0 values, the fluorine-containing LAS glass-ceramic exhibits a higher emission intensity and a longer lifetime. Under 394 nm excitation, the fluorine-containing LAS glass-ceramic presents a warm and nearly pure red emission, characterized by a correlated color temperature of less than 3300 K and a color purity approaching 100 %. Time-resolved emission spectra support the photoluminescent stability of the Eu3+ ions. According to the Judd-Ofelt theory and spectral results, the fluorine-containing LAS glass-ceramic possesses lower Ω2/Ω4 and asymmetry ratios, leading to a more symmetrical local environment for the Eu3+ ions. Benefiting from its enhanced red emission, the 5D0→7F2 transition in the fluorine-containing LAS glass-ceramic exhibits a higher branching ratio (69.28 % > 50 %), emission cross-section (8.94 × 10−22 cm2), and gain bandwidth (12.12 × 10−28 cm3). Additionally, temperature-dependent photoluminescence spectra substantiate the excellent thermal stability of the Eu3+ doped fluorine-containing LAS glass-ceramic. Specifically, the intensity of the 5D0→7F2 transition at 150 °C remains 80 % of the initial intensity. Therefore, the Eu3+ doped multi-component transparent oxyfluoride aluminosilicate glass-ceramic has a significant competitive advantage in the field of red lasers and trichromatic WLEDs.

The preferential orientation controlling for efficient Sb2S3 and low Se content Sb2SeyS3-y indoor photovoltaics

Sb2S3 is a promising absorber material for indoor photovoltaics due to the appropriate direct bandgap of 1.75 eV, high element abundance, low toxicity, stability, and single phase. Considering the indoor lighting irradiance is very low and the resulting carrier numbers are relatively less and Sb2S3 is quasi-one-dimensional crystal structure, the preferential orientation controlling of Sb2S3 is very important to improve the power conversion efficiency (PCE) of Sb2S3 indoor photovoltaics. Herein, Sb2S3 and low Se content Sb2SeyS3-y films are prepared by chemical bath deposition and the preferential orientation of Sb2S3 films is controlled by introducing SbCl3 and selenourea in the growth solution. The uniformity of the S and Se distribution in low Se content Sb2SeyS3-y films is adjusted by introducing EDTA-2Na. Using the warm white LED with a color temperature of 3347 K and illuminance of 1000 lux, Sb2S3 and low Se content Sb2SeyS3-y indoor photovoltaics achieve the PCE of 16.58% for Sb2S3 and 17.62% for Sb2SeyS3-y, which is the highest PCE for antimony chalcogenide indoor photovoltaics. Therefore, the preferential orientation controlling by introducing SbCl3 and selenourea into the growth solution is an efficient strategy for fabricating high-efficiency Sb2S3 and low Se content Sb2SeyS3-y indoor photovoltaics.

Effects of Shading Nets Color on the Internal Environmental Conditions, Light Spectral Distribution, and Strawberry Growth and Yield in Greenhouses.

Greenhouses are used to create the appropriate environment for plant growth. Controlling the level of lighting using shading nets is one of the most commonly used methods for making suitable environmental modifications in greenhouses. The objective of this study was to examine the impact of three colored shading nets (green, black, and beige at shading rates of 50%) on inside air temperature, relative humidity, and spectral distribution of light in a greenhouse, as well as their effect on the growth and yield of strawberry plants. Data were collected during winter (December and January) and spring (March and April) months from shaded and unshaded blocks. The green net had the highest transmittance to solar radiation (τSR) during the two periods (38% and 35%, respectively) and the highest transmittance to photosynthetically active radiation (τPAR) of 34% during spring months, while the beige net had the highest τPAR of 27% during winter months. The black net had the smallest τPAR values during the two periods (22% and 29%, respectively). The lowest total light levels per season for solar radiation (SR) and photosynthetically active radiation (PAR) (746.8 and 293.7 MJ·m-2, respectively) were obtained under the black net, compared with (906.7 and 320.8 MJ·m-2, respectively) for the beige net, and (969.6 and 337.2 MJ·m-2, respectively) for the green net. The ratio of PAR to SR (PAR:SR) was 41% and 44% outside and inside the greenhouse for the control (without shade), respectively. The black net had the highest ratio of PAR:SR (39%) among the treatment nets. The green net transmitted more light in the blue-green region (400 to 570 nm) and transmitted the highest photon flux at 480 nm, while the beige net increased the infrared radiation flux from 730 nm and above and transmitted the highest photon flux at 604 nm. The study found that the green net increased the ratio of blue to red light (B/R), while the beige and green nets reduced the red to far-red light (R/FR) ratio. The photosynthetic rate, conductance to water, and transpiration were significantly higher for strawberries grown under the beige net. These results indicate that the beige net positively influenced leaf and stem characteristics, leading to improved strawberry yields. The best yields of strawberries were obtained under the beige net and the control group (no shade), surpassing the yields achieved under the black net by 26.3% and 21.4%, respectively.

Light Quality Influence on Growth Performance and Physiological Activity of Coleus Cultivars

This study investigates the influence of different light qualities, including red, green, blue, purple, and white lights, on the growth, physiological activity, and ornamental characteristics of two Coleus cultivars. Emphasizing the importance of leveraging phenotypic plasticity in plants within controlled environments, using light quality is a practice prevalent in the ornamental industry. The research explores the varied responses of two Coleus cultivars to distinct light spectra. The key findings reveal the efficacy of red light in enhancing shoot and leaf parameters in C. ‘Highway Ruby’, while red and green light exhibit comparable effects on shoot width and leaf dimensions in C. ‘Wizard Jade’. White light-emitting diodes (LEDs), particularly with color temperatures of 4100 K and 6500 K, promote root length growth in the respective cultivars. Moreover, chlorophyll content and remote sensing vegetation indices, including chlorophyll content (SPAD units), the normalized difference vegetation index (NDVI), the modified chlorophyll absorption ratio index (MCARI), and the photochemical reflectance index (PRI), along with the chlorophyll fluorescence, were significantly affected by light qualities, with distinct responses observed between the cultivars. In summary, this study highlights the transformative potential of LED technology in optimizing the growth and ornamental quality of foliage plants like Coleus, setting a benchmark for light quality conditions. By leveraging LED technology, producers and nursery growers access enhanced energy efficiency and unparalleled versatility, paving the way for significant advancements in plant growth, color intensity, and two-tone variations. This presents a distinct advantage over conventional production methods, offering a more sustainable and economically viable approach for increased plant reproduction and growth development. Likewise, the specific benefits derived from this study provide invaluable insights, enabling growers to strategically develop ornamental varieties that thrive under optimized light conditions and exhibit heightened visual appeal and market desirability.

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

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

Highly Efficient Red Emission from Novel Sm3+ Doped Na3La(PO4)2 Nanophosphors for Optoelectronic Applications.

Solution combustion procedure was used to create a succession of Na3LaxSm1 - x(PO4)2 (x = 0.01-0.15mol) nanocrystals that generate a warm deep reddish light. Both HR-TEM and X-ray diffraction examinations were used to examine the morphology and crystalline phase analysis. Energy-dispersive X-ray analysis (EDAX) approves the elemental examination. The luminescence spectrum exhibits a decent reddish-orange emission at 700nm wavelength upon near-UV illumination, which aligns with the electronic transition 4G5/2 → 6H11/2. According to Dexter's idea, nearest neighbor interlinkages are responsible for the concentration quenching that occurs after the Sm3+ ion composition reaches 6 mol%. Additionally, a detailed evaluation of the radiative lifespan (0.7519 ms), quantum efficiency (77%), Non radiative rate (307.40), color temperature (3170K), color purity (99.2%) and color coordinates (0.652, 0.338) was conducted. The optical characteristics that have been observed indicate that Sm3+ doped Na3La(PO4)2 phosphors could be a good option for improving WLED efficiency and color quality.

Tuning β-Si3Al3O3N5 phosphors by Eu or Ce doping for white light-emitting diodes (wLEDs)

SiAlON-based phosphors have garnered considerable attention in the field of white lighting owing to their excellent thermal stability, and rare earth doped SiAlON-based phosphors are expected to be used in a new generation of lighting sources. In this work, Eu2+ or Ce3+ doped Si3Al3O3N5 phosphors were synthesized by high temperature solid phase method. The microstructure of the phosphors exhibited irregular grain. The two phosphors exhibit green and cyan luminescence under 365 nm excitation, which are derived from the 5d-4f transitions of Eu2+ and Ce3+, respectively. The quenching concentrations are 3 % and 4 % for Eu2+ and Ce3+doped phosphors, respectively. The fluorescence intensity of Eu2+ and Ce3+ activated SiAlON powders decreased to 50 % of the room temperature intensity at 179 °C and 170 °C, respectively. The thermal activation energy values of the two phosphors were 0.35 eV, and the coordinate configuration diagram was constructed to comprehensively analyze the thermal quenching behavior of phosphors. Finally, the two phosphors powders were mixed with red and blue fluorophore to obtain white LEDs, showing low color temperature, high color rendering, high power unsaturation and long half-life. The SiAlON-based phosphors with excellent thermal stability obtained in this work achieve different wavelengths of luminescence in the green region. The results show that the β-Si3Al3O3N5 phosphor can be used as a candidate material for high-quality green light supplement for wLEDs.

Study on the Performance of Deep Red to Near-Infrared pc-LEDs by the Simulation Method Considering the Distribution of Phosphor Particles.

Effectively utilizing deep red to near-infrared (DR-NIR) phosphors to achieve the optimal performance of NIR phosphor-converted white LEDs (DR-NIR pc-wLEDs) is currently a research hotspot. In this study, an optical model of DR-NIR pc-wLEDs with virtual multilayer fluorescent films was established based on the Monte Carlo ray-tracing method. Different gradient distributions of the particles were assigned within the fluorescent film to explore their impact on the optical performance of pc-LEDs. The results show that, for the case with single-type particles, distributing more DR-NIR particles far from the blue LED chip increased the overall radiant power. The distribution of more DR-NIR particles near the chip increased the conversion ratio from blue to DR-NIR light. The ratio of the 707 nm fluorescence emission intensity to the 450 nm excitation light intensity increased from 1:0.51 to 1:0.28. For multiple-type particles, changes in the gradient distribution resulted in dual-nature changes, leading to a deterioration in the color rendering index and an increase in the correlated color temperature, while also improving the DR-NIR band ratio. The reabsorption caused by the partial overlap between the excitation band of the DR-NIR particles and the emission band of the other particles enhanced the radiant power at 707 nm. Distributing DR-NIR phosphor particles closer to the chip effectively amplified this effect. The proposed model and its results provide a solution for the forward design of particle distributions in fluorescent films to improve the luminous performance of DR-NIR pc-wLEDs.

Photo-thermal decoupling CdTe PV windows with selectively near-infrared absorbing ATO nanofluids

Solar energy conversion and utilization are crucial for buildings. Photovoltaic windows are a promising path to improving building energy efficiency. This study proposes a novel photo-thermal decoupling cadmium telluride (CdTe) PV windows with selectively near-infrared absorbing antimony-doped tin oxide (ATO) nanofluids. The PV-ATO window features four concentrations (200/400/800/1000 ppm). Hot box experiment results show that PV-ATO windows can reduce the peak indoor air temperature by up to 2.56, 2.06, 2.86, and 2.72 °C respectively, while the corresponding peak illuminance is cut by 13.01 %, 12.37 %, 17.40 %, and 56.28 %. Measured transmitted spectra's correlated color temperature (CCT) of the PV-Water and PV-ATO windows are in the range of 4811.0～5271.0 K; color render index (Ra) is between 95.7～98.8; color fidelity index (Rf) is between 96.9～99.1; color gamut index (Rg) is between 97.6～99.3. Regarding color rendering performance, the PV-ATO windows can outperform conventional windows. Energy simulation results show that the comprehensive energy-saving ratios of different PV-ATO windows in Guangzhou, Changsha, Chongqing, and Wuhan can achieve −11.27 %, −20.38 %, −0.08 %, and −5.17 %. The study points to low concentrations of ATO nanofluids (200 ppm) as the recommended value.

Substitutional effects of the anionic group systems [BO33−], [PO43− ], and [SO42−] on the down-conversion photoluminescence properties of Y2O3:Er3+ nanophosphors

A series of Y2O3, Y2O3: Er3+ (1 %) and Y2O3-AG: Er3+ (1 %) (where AG = BO33−, PO43−, and SO42−) nanophosphors were prepared via a chemical combustion technique. The primary X-ray powder diffraction results showed that the Y2O3:Er3+ phosphor materials crystallized into a cubic standard structure, while the Y2O3-AG: Er3+ phosphor materials transformed to hexagonal and tetragonal structures for the [PO43−] and [BO33−]-based phosphors, respectively. However, no changes were observed for the [SO42−]-based phosphor materials. The scanning electron microscope micrographs revealed that the particles were formed in the nanometre range with different sizes and shapes. The fourier-transformed infrared spectra showed the presence of various structural groups in the pure Y2O3 and Y2O3-AG: Er3+ phosphors. In addition to that, the optical bandgap energy values were obtained using the diffuse reflection spectra (DRS) spectra and Kubelka-Munk function theory. Under UV-379 nm excitation for the Y2O3-AG: Er3+ phosphors, the Y2O3–SO4: Er3+ emitted the most intense green light at 563 nm wavelength. The Commission Internationale de l'Elcairage colour coordinates and correlated color temperature values indicated that the Y2O3:Er3+, Y2O3-PO4:Er3+, and Y2O3–SO4:Er3+ phosphor materials are potential candidates for producing enhanced green color components in white light-emitting diode (w-LED) applications.