High Correlated Color Temperature Research Articles

Research on the influence of light source characteristics on traffic visual distance in foggy areas at night

Adverse weather such as fog will reduce drivers' visual recognition ability, and important visual information in the driving will be weakened and even lost, which brings risks to driving safety. This paper sets out to explore causes for the decline in driving visual ability in foggy sections at night based on drivers' visual recognition demand mechanism. The purpose is to study the influence of light source characteristics on visual distance under open traffic conditions. Through an outdoor visual recognition test, data were collected on the visual recognition distances of 12 car drivers to standard gray small targets, under different light source characteristics and meteorological visibility conditions. Results revealed that the latter conditions, along with illuminance and correlated color temperature affected drivers' visual recognition ability in low meteorological visibility sections at night. At the same illuminance and meteorological visibility, a light source with high correlated color temperature could improve visual distance. The multivariate power function model of meteorological visibility, illuminance at the target and driver's visual distance in foggy areas were obtained by fitting. The research methods and conclusions could provide technical reference for improving traffic visual distance at night, and thus help lay a foundation for road construction and traffic control technology in foggy areas.

Alerting effects of light in healthy individuals: a systematic review and meta-analysis.

Light plays an essential role in psychobiological and psychophysiological processes, such as alertness. The alerting effect is influenced by light characteristics and the timing of interventions. This meta-analysis is the first to systematically review the effect of light intervention on alertness and to discuss the optimal protocol for light intervention. In this meta-analysis, registered at PROSPERO (Registration ID: CRD42020181485), we conducted a systematic search of the Web of Science, PubMed, and PsycINFO databases for studies published in English prior to August 2021. The outcomes included both subjective and objective alertness. Subgroup analyses considered a variety of factors, such as wavelength, correlated color temperature (CCT), light illuminance, and timing of interventions (daytime, night-time, or all day). Twenty-seven crossover studies and two parallel-group studies were included in this meta-analysis, with a total of 1210 healthy participants (636 (52%) male, mean age 25.62 years). The results revealed that light intervention had a positive effect on both subjective alertness (standardized mean difference (SMD) = –0.28, 95% confidence interval (CI): –0.49 to –0.06, P = 0.01) and objective alertness in healthy subjects (SMD = –0.34, 95% CI: –0.68 to –0.01, P = 0.04). The subgroup analysis revealed that cold light was better than warm light in improving subjective alertness (SMD = –0.37, 95% CI: –0.65 to –0.10, P = 0.007, I2 = 26%) and objective alertness (SMD = –0.36, 95% CI: –0.66 to –0.07, P = 0.02, I2 = 0). Both daytime (SMD = –0.22, 95% CI: –0.37 to –0.07, P = 0.005, I2 = 74%) and night-time (SMD = –0.32, 95% CI: –0.61 to –0.02, P = 0.04, I2 = 0) light exposure improved subjective alertness. The results of this meta-analysis and systematic review indicate that light exposure is associated with significant improvement in subjective and objective alertness. In addition, light exposure with a higher CCT was more effective in improving alertness than light exposure with a lower CCT. Our results also suggest that both daytime and night-time light exposure can improve subjective alertness.

Anchoring of red perovskite nanocrystals on YAG:Ce phosphor for high color rendering index WLEDs

Widespread application of YAG:Ce-based white light-emitting diodes (WLEDs) is being challenged for their poor color rendering index (CRI) and high correlated color temperature (CCT) due to the lack of red emission. Organic-inorganic hybrid perovskite nanocrystals (MAPbX3 PNCs, X = Cl, Br, I or mixture of them), presenting high photoluminescence quantum yield, tunable emission color and simple fabrication process have been recognized as promising red-emitting component for warm WLEDs. However, additional protection process for PNCs always needed due to their poor stability, which complicates the fabrication procedures of WLEDs. Besides, nano-sized PNCs and micron YAG:Ce powder display different sinking behavior in silicone, which also hard to ensure the uniform distribution of the two components and subsequently stable optical characteristics of the device. Herein, a one-pot anchoring strategy is implemented to realize the enhanced thermal and photo-stabilities of in-situ generated red-emitting MAPbBr0.5I2.5 PNCs and simultaneously strong interaction between the PNCs and YAG:Ce to form PNCs@A-YAG composite, which greatly simplifies the processes, and also avoids the uneven distribution of phosphor and PNCs in silicone. Furthermore, the WLED, fabricated by PNCs@A-YAG and a commercial blue chip, exhibits high CRI of 92, low CCT of 4755 K, and super high saturated red color R9 of 95, which are of vital importance in achieving warm white light for indoor lighting applications. This work could promote the practical application of perovskite nanocrystals in the field of high color rendering index WLEDs.

Blue-light-excitable broadband yellow-emitting CaGd2HfSc(AlO4)3:Ce3+ garnet phosphors for white light-emitting diode devices with improved color rendering index

The current commercial white light-emitting diodes (LEDs) are generally based on the combination of blue LED chips and Y3Al5O12:Ce3+ yellow phosphors. However, because of the lack of red component, such white LED devices exhibit cool white-light emissions with low color rendering index (Ra < 75, R9 < 0). Therefore, it is urgent to discover new blue-light-excitable yellow-emitting phosphors with enhanced red emissions for fabricating high color-quality white LEDs. In the present work, we demonstrate a novel broadband yellow-emitting CaGd2HfScAl3O12:Ce3+ garnet phosphor for blue-light-excited white LEDs with improved color rendering index. The as-prepared CaGd2HfScAl3O12:Ce3+ garnet phosphor possesses a cubic structure with Ia3¯d space group, and the unit cell parameters of the representative CaGd2HfScAl3O12:2%Ce3+ phosphor are a = b = c = 12.450 Å, α = β = γ = 90°, and V = 1,929.59(4) Å3. Impressively, we find that the CaGd2HfScAl3O12:Ce3+ garnet phosphor shows an intense absorption band in the 300–500 nm wavelength range with a maximum at 452 nm owing to the 4f→5d transition of Ce3+ ions. On 452 nm excitation, the optimal CaGd2HfScAl3O12:2%Ce3+ sample exhibits a broad asymmetric yellow emission band in the wavelength range of 470–750 nm with peak at 564 nm and full width at half maximum of 151 nm. The Commission Internationale de l’Eclairage chromaticity coordinates and internal quantum efficiency of the CaGd2HfScAl3O12:2%Ce3+ sample are (0.4485, 0.5157) and 30.4%, respectively. Finally, a white LED device is fabricated by combing a 450 nm blue LED chip with commercial Y3Al5O12:Ce3+ yellow-emitting phosphor, which generates white light with low color rendering index (CRI; Ra = 74.7, R9 = −12.7) and high correlated color temperature (CCT = 6,554 K) under the 60 mA driving current. In sharp contrast, another white LED device, which is made by coating our as-prepared CaGd2HfScAl3O12:2%Ce3+ yellow-emitting phosphors onto the surface of a 450 nm blue LED chip, produces white-light emission with high CRI value (Ra = 84.5, R9 = 26.3) and relatively low CCT of 5,649 K. This work reveals that the newly discovered broadband yellow-emitting CaGd2HfScAl3O12:Ce3+ phosphors can serve as a potential color converter in high-color-quality phosphor-converted white LEDs.

Robust thermal performance and color purity of samarium based deep red emitting phosphor for near-UV chip-based high-color-rendering

In the progress of LED phosphors, the chemical stability, thermal stability, and color purity was not usually given due attention. However, the most critical problems of WLEDs are the deficit in the red-spectral region, stability, low color-rendering index (CRI) and high correlated color temperature (CCT) limit its efficiency for vivid application. Herein, the Ca3YGa3B4O15:xSm3+ (CYGB:xSm3+) were prepared by a solid-state route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), diffuse reflection spectroscopy (DRS), and as well as photoluminescence (PL) spectra are used to exemplify the resulting samples. The structure and the Sm3+ dopants in the cation-borate phosphors were quantified, signifying the importance at Ca and Y sites. Under ultraviolet radiation-induced bright deep-red emissions with high color-purity up to 97.5%. The energy-migration (EM) between the Sm3+ ion was investigated both empirically and theoretically in the region of Sm3+ contents. Several theoretical-models were employed to simulate the lifetime of Sm3+ at various-concentrations, and the processes were investigated as a forced-electric dipole. The chemical-stability of CY0.95GB:0.05Sm3+ has also been investigated in this work. Interestingly, the CY0.95GB:0.05Sm3+ showed exceptional thermal-quenching resistance of>91.2% intensity at 400 K. The WLED containing CY0.95GB:0.05Sm3+ blended with the BAM:Eu2+ and CYAB:Tb3+ phosphor demonstrated low CCT ≈ 3843 K and high CRI ≈ 91.9. These findings were healthier than the industrial WLED having Y3Al5O12:Ce3+ and blue-LED.

Optimized lighting energy consumption for non-visual effects: A case study in office spaces based on field test and simulation

Recently, the non-visual effects of the light environment have received increasing attention. Some standards have proposed evaluation metrics for non-visual effects in office spaces to ensure the health and well-being of occupants. Non-visual metrics are new requirements for indoor light environments, whose impacts on lighting adjustment and ultimate lighting energy performance are currently unknown. Therefore, this study aimed to present a workflow to obtain optimal light outputs considering non-visual lighting requirements, in addition to traditional visual requirements. This workflow was implemented to calculate the annual lighting energy consumption under different light correlated color temperatures (CCTs), daylight conditions, and standard requirements for an actual office scenario. As deduced from the results, adding non-visual requirements may significantly increase the lighting energy consumption by 57 %. Furthermore, daylight and light with a higher CCT are beneficial for non-visual energy-saving. The additional non-visual requirements will not increase the lighting energy consumption under favorable daylight conditions. The 5500 K light can save up to 20 % of the annual lighting power consumption than the 4000 K light. The presented workflow and conclusions contribute to engineering office environments with enhanced lighting, better circadian stimulus, and improved office lighting energy efficiency.

The excellent luminous efficiency and high thermal stability of phosphor-in-glass for high-power laser

At present, fluorescent glass mainly emits a single yellow light. The characteristic of green and red luminescent materials limits its omni-directional combination with yellow light materials, resulting in high correlated color temperature and low color rendering index of laser lighting devices, which seriously reduces the quality of laser lighting. Therefore, the development of multi-color fluorescent glass to improve the color quality is a huge challenge in laser lighting technology. In this research, the glass matrix that can be compounded with multi-color phosphors is proposed to solve the problems of phosphor decomposition, oxidation, corrosion, and blackening during the vitrification process. Surprisingly, a 50 wt. % Ce:YAG&amp;1.5 wt. % CaAlSiN3-PiG (50 Y&amp;1.5 R-PiG) sample exhibits an excellent internal quantum efficiency of 94% and achieves a high luminous efficiency of 184 lm/W under laser irradiation. Moreover, an ultrahigh luminous efficiency of 331 lm/W is realized by using a laser device with a heat sink. It demonstrated that Y&amp;R-PiG can own excellent application prospects in high-quality lighting fields, such as laser displays and automobile headlights.

Effect of Eu2+ doping on photoluminescence of Al2O3:Tb3+ functional coatings formed by plasma electrolytic oxidation

Multifunctional coatings of Al2O3 co-doped Tb3+ or Tb3+/Eu2+ were synthesized by the rapid and facile plasma electrolytic oxidation method on pure aluminium substrate. SEM & EDS analysis revealed porous structure independent on the doping concentration, with uniform distribution of co-doped rare-earth elements and incorporated concentrations proportional to the rare-earth particles concentrations added to the basic electrolyte. The gamma phase of Al2O3 increases to the expense of the alpha phase of Al2O3 with rising content of Tb3+. The addition of Eu2+ caused no further phase transformations. The photoluminescence (PL) excitation spectrum of Al2O3:Tb3+ was featured by sharp peaks (due to inter-configurational 4f transitions of Tb3+) and orders of magnitude larger broad-band in the middle ultraviolet region ascribed to the 4f→4f5d transitions. The PL emission spectrum was featured by the typical 4f→4f transitions of Tb3+, with maximum green emission at 541 nm and intensity proportional to the doping concentration. As the Eu2+ emission and Tb3+ excitation overlap, the concentration dependent energy transfer Eu2+→Tb3+ (of dipole-dipole character) occurred, resulting in the 20x increase in total PL and 3.2x increased Tb3+ PL. The PL emission color of Al2O3:Tb3+ was green and concentration independent, while of Al2O3:Eu2+/Tb3+ the color was in the domain of cold white with high correlated color temperature, which slightly decreased with increasing Eu2+ concentration.

Is the use of high correlated color temperature light at night related to delay of sleep timing in university students? A cross-country study in Japan and China

BackgroundBlue-enriched white light at night has the potential to delay the circadian rhythm in daily life. This study was conducted to determine whether the use of high correlated color temperature (CCT) light at home at night is associated with delay of sleep timing in university students.MethodsThe survey was conducted in 2014–2015 in 447 university students in Japan and 327 students in China. Habitual sleep timing and type of CCT light at home were investigated by using a self-administered questionnaire. The Japanese students were significantly later than the Chinese students in bedtime, wake time, and midpoint of sleep. They were asked whether the lighting in the room where they spend most of their time at night was closer to warm color (low CCT) or daylight color (high CCT). The amount of light exposure level during daily life was measured for at least 1 week by the use of a light sensor in 60 students in each country.ResultsThe percentages of participants who used high CCT lighting at night were 61.6% for Japanese students and 80.8% for Chinese students. Bedtime and sleep onset time on school days and free days were significantly later in the high CCT group than in the low CCT group in Japan. The midpoint of sleep in the high CCT group was significantly later than that in the low CCT group on free days but not on school days. On the other hand, none of the sleep measurements on school days and free days were significantly different between the high CCT and low CCT groups in China. Illuminance level of light exposure during the night was significantly higher in Japanese than in Chinese, but that in the morning was significantly higher in China than in Japan.ConclusionsThe use of high CCT light at night is associated with delay of sleep timing in Japanese university students but not in Chinese university students. The effects of light at night on sleep timing and circadian rhythm may be complicated by other lifestyle factors depending on the country.

Optical and Dynamic Properties of ZnGa2S4

ZnGa2S4 luminescent compound is prepared by solid‐state reaction, which is confirmed by X‐ray diffraction to have a tetragonal structure. The photoluminescence (PL) emission and excitation spectra, infrared (IR) reflectivity and Raman scattering of the defective ZnGa2S4 compound are studied experimentally. High stability of the shape and peak positions of the PL spectra is observed in a wide range temperature range (100–290 K). It was determined that PL intensity increases with decreasing temperature. Higher correlated color temperature (CCT) value &gt;6000 K implies the suitability of using this material for light emitting diodes. Five modes of optical phonons are found in both IR reflectance and Raman spectra of ZnGa2S4 and identified from point group symmetry analysis. The calculations of the dynamic properties are carried out within the framework of the density functional theory (DFT) with full optimization of the lattice parameters. Results of calculations show that, the phonon‐dispersion curve is sensitive to S–Se replacement in ZnGa2S4 and gives rise to clearly pronounced energy gaps in the phonon spectrum.

Robust thermal performance of red-emitting phosphor composites for white light-emitting diodes: Energy transfer and oxygen-vacancy induced electronic localization

Ce3+ ion can effectively sensitize Sm3+ ion via energy transfer, and this phenomenon can led to the development of white light-emitting diodes (WLED). However, interestingly, high correlated color temperature (CCT), poor color-rending index (CRI), poor thermal stability, and low efficacy of available red phosphor still pose immense challenges. Herein, we undertook a combined analysis: X-ray diffraction (XRD), crystal refinement, electron spin resonance (ESR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and diffuse reflection spectroscopy (DRS). We also observed the optical properties of the resulting samples. The Ce3+ and Sm3+ dopants on the Sr2+ and La3+ sites in the mixed cation borate Sr3LaAl3B4O15 (SLAB) phosphors were quantitatively evaluated. A cerium ion merged as a sensitizer, improving the red emission intensity by enhancing it 3.9 times. The energy transfer (ET) between Ce3+ and Sm3+ was examined experimentally and with theoretical models as a function of Ce3+ concentrations at ambient temperatures. Several theoretical models were employed to simulate the luminescence decays of Ce3+ and Sm3+ doped samples at different doping levels and their transfer mechanisms were studied depending on forced electric dipole at each ion. Notably, the electronic sites created by the oxygen vacancies around the Ln3+ ions can effectively justify the highly efficient bluish-red phosphor. Additionally, the SL0.95AB:0.02Ce3+,0.03Sm3+ exhibited outstanding thermal-quenching (TQ) resistance and has > 94.8% intensity at 425 K. WLEDs made with the use of SL0.95AB:0.02Ce3+,0.03Sm3+ furnished an exceptional CRI exceeding 88 and low at CCT 4503 K. These results are superior to the parameters of commercial WLED containing Y3Al5O12:Ce3+ phosphor and blue LED chip (CCT≈7746 K, CRI≈75), and they could be a cornerstone for the fabrication of warm WLEDs.

Realizing high-performance color-tunable WOLED by adjusting the recombination zone and energy distribution in the emitting layer

Color-tunable white organic light-emitting diodes (CT-WOLEDs) having daylight chromaticity and a wide correlated color temperature (CCT) span can mimic our circadian cycle and realize application for lighting or decoration. The effects of the recombination zone and energy distribution on the electro-optical properties and color span are investigated in this paper. We find that it is beneficial to expand the CCT span by increasing the distance between the red ultrathin phosphorescent emissive layer and the center of the recombination zone. By increasing the concentration (y) of mCP in mixed host material in the emitting layer and the thickness (z nm) of the red ultrathin phosphorescent emissive layer, the CCT spans can be expanded towards high CCT and low CCT, respectively. The widest CCT span reaches 4032 K (2391–6423 K) in a simple all-phosphorescent CT-WOLED with a maximum luminance and power efficiency of 9249 cd m−2 and 15.35 lm W−1, respectively.

Full-visible-spectrum emission with high color rendering index and low correlated color temperature enabled by a single-phased phosphor of α-Sr2V1.98P0.02O7: 0.5% Eu3+

A single-phased warm white phosphor of α-Sr2V1.98P0.02O7: 0.5 % Eu3+ with low correlated color temperature (CCT) and high color rendering index (CRI) was synthesized by high temperature solid phase method. By changing the ratio of PO43−/VO43−, the emission intensity of VO43− and the energy transfer efficiency of VO43−→Eu3+ can be effectively tuned, and the full-spectrum warm white light emission of phosphors in the range of 400−700 nm can be realized. Moreover, the temperature-dependent emission spectra and thermal quenching properties were investigated in detail. On this basis, the WLED prototype devices were packaged with the synthesized phosphors α-Sr2V1.98P0.02O7: 0.5 % Eu3+ and 365 nm near-ultraviolet (NUV) chips and high-quality warm white light emission with CCT = 3188 K and CRI Ra = 93.5 were achieved. These findings provide new insights into exploring single-phased white phosphors for NUV-pumped warm w-LEDs with high CRI property and low CCT value.

Utilizing CaCO&lt;sub&gt;3&lt;/sub&gt;, CaF&lt;sub&gt;2&lt;/sub&gt;, SiO&lt;sub&gt;2&lt;/sub&gt;, and TiO&lt;sub&gt;2&lt;/sub&gt; phosphors as approaches to the improved color uniformity and lumen efficacy of WLEDs

The two elements that are most favorable in the quality evaluation for phosphor-converted LEDs (pcLEDs) these days are the chromatic homogeneity and the lumen output. In this study, a thorough research on enhancing color uniformity and luminous flux of pcLEDs that have a high correlated color temperature (CCT) of 8500K is carried out. The scattering enhancement particles (SEPs): CaCO 3 , CaF 2 , SiO 2 , and TiO 2 are used to accomplish the goal by adding them to a yellow phosphor compounding Y 3 Al 5 O 12 :Ce 3+ , and comparing their characteristics afterwards. LightTools program is used to build an optical simulation and Mie-scattering theory helps to examine the achieved results. Specifically, the parameters included in SEPs’ scattering calculation are the scattering coefficients, the anisotropic scattering, the reduced scattering, and the scattering amplitudes at 455 nm and 595 nm. The outcomes presented that compared to other SEPs, TiO 2 particles can yield the highest chromatic homogeneity. However, the lumen output reduces considerably as TiO 2 concentration greatly increases while it can be bettered when using SiO 2 particles with any particle size. For CaCO 3 particles, the color deviation of 620 K CCT can be reduced with 30% concentration, leading to the recommendation of using CaCO 3 to promote the CCT homogeneity and luminescence efficiency.

Single phase white LED phosphor Ca3YAl3B4O15:Ce3+,Tb3+,Sm3+ with superior performance: Color-tunable and energy transfer study

The white light-emitting diodes, contributing as a light initiator for the succeeding generation, is now becoming a consistently developing and attractive research area. However, the weak thermal stability, high correlated color temperature (CCT), and low color rendering (Ra) restrict its effectiveness for large-scale implementation. In this work, we reported for the first time the incorporation of rare-earth ions Ce3+-Tb3+-Sm3+ into Ca3YAl3B4O15 (CYAB) in the fabrication of WLEDs, which showed tunable photoluminescence properties to accomplish exceptional thermal stability, single-phase white light emission, and efficient energy transfer among Ce3+, Tb3+, Sm3+ ions, respectively. The crystal structure and the rare earth ion dopants in the cation borate CYAB phosphors were quantitatively evaluated, that highlighting the preferences at 9-fold-coordinated Y sites. The sensitization effects were studied by evaluating the photoluminescence, lifetime curves, and quantum efficiencies, respectively. Besides this, the CY0.45AB:0.50Tb3+,0.05Sm3+ and CY0.65AB:0.03Ce3+,0.20Tb3+,0.12Sm3+ phosphors possess significant resistance towards thermal quenching phenomena. The white LED either containing CY0.45AB:0.50Tb3+,0.05Sm3+ phosphor blended with the commercial blue phosphor or the single-phase WLED only containing CY0.65AB:0.03Ce3+,0.20Tb3+,0.12Sm3+ phosphor exhibited warm white emissions either with low CCT ≈ 4543 K or 3913 K and high Ra with 86.0 or 84.4, respectively. These results are superior to the commercial WLED containing Y3Al5O12:Ce3+ phosphor and blue LED chip (CCT ≈ 7746 K, Ra ≈ 75), that furnish either as a good candidate for the fabrication of warm WLED.

Blue-Light Hazard of Light-Emitting Diodes Assessed with Gaussian Functions.

The high blue proportion of phosphor-conversion white-light emitting diodes (pc-LEDs), especially of those with higher correlated color temperatures (CCT), raises concern about photochemically induced retinal damages. Although almost all general lighting service LEDs are safe, other applications exist, like spotlights for theatres or at construction sites, that can pose a severe blue-light hazard (BLH) risk, and their photobiological safety must be assessed. Because of required but challenging radiance measurements, a calculative approach can be supportive for risk assessment. It is the aim of this work to exploit Gaussian functions to study LED parameter variations affecting BLH exposure. Gaussian curve approximations for color LEDs, the BLH action spectrum, and the spectral luminous efficiency for photopic vision enabled analytically solving the BLH efficiency, , and the BLH efficacy of luminous radiation, . It was found that sigmoidal functions describe the CCT dependence of and for different color LEDs with equal spectral bandwidth. Regarding pc-LEDs, variations of peak wavelengths, intensities, and bandwidths led to linear or parabolic shaped chromaticity coordinate correlations. and showed pronounced CCT dependent extrema that might be exploited to reduce BLH. Finally, an experimental test of the presented Gaussian approach yielded its successful applicability for color and pc-LEDs but a minor accuracy for blue and green LEDs.

Preferred skin tones reproduction of three ethnic groups under different ambient lighting conditions

A large-scale experiment was conducted to investigate facial image quality on mobile phones. There were 8 original facial images from 4 skin tone types, each included a male and a female image. Each image was captured at 6500K and they were rendered to have 5 CCT (correlated colour temperature) and 5 Duv (the shifts away from the Blackbody locus) levels via CAT02 chromatic adaptation transform to simulate the effect of the images captured under 25 different lighting conditions. Each image was assessed under 9 ambient lighting conditions( including one dark condition) by 90 observers from 3 ethnic groups (Caucasian, Chinese and South Asian), each 30 observers. Preferred facial skin tone ellipse was established by maximizing the correlation coefficient between the model predicted probability and the preference percentage from the visual results. Four types of preferred skin tones had small differences in hue angle and chroma, but concentrated into a small colour region, about [24.7, 46.1°] for Cab* and hab values respectively. All ethnic group preferred images taken under illuminants having high CCT (6500-8000 K). It was also found that the chroma of the preferred skin tones will slightly increase as the ambient lighting CCT decrease.

Controlling the Surface Properties of TiO2 for Improvement of the Photo-performance and Color Uniformity of the Light-emitting Diode Devices

The photo-performance and color uniformity of the light-emitting diodes (LEDs) were enhanced by controlling the surface properties of the titanium dioxide (TiO2) particles as light scatting materials using a sol-gel-based surface modification method. Silane coupling agents of different carbon chain lengths (C3–C16) were introduced onto the TiO2 surface for investigating the light scattering effect depending on the TiO2 dispersibility in the encapsulant. The dispersibility of the modified TiO2 particles was greater than that of the as-prepared TiO2 particles (1.6–2.5 times). The dispersibility of TiO2 improved with the increasing carbon chain length of silane (C3–C6). However, the dispersibility did not increase but reduced when the carbon chain length was considerably long (C16) because the TiO2 surface was more hydrophobic than the encapsulant. After the fabrication of the LED devices, the TiO2-loaded LED device showed high photometric flux and low correlated color temperature despite using the same concentration of phosphor (3.0wt.% with respect to the added silicone resin). Furthermore, the photo-performance and color uniformity improved when the TiO2 dispersibility was increased. This can be attributed to the enhancement of light scattering in the LED package when the interfacial affinity of the TiO2/encapsulant was improved.

SrBaSiO4:Eu2+ phosphor: a novel application for improving the luminous flux and color quality of multi-chip white LED lamps

This paper described in detail the chromatic homogeneity and luminous flux influences in producing better quality white LED devices with various phosphor layers (MCW-LEDs). The method is to let Eu2+-activated strontium–barium silicate (SrBaSiO4:Eu2+) mixed with their phosphor compounding, which results in notable impact on lighting performance. The increase in concentration of yellow-green-emitting SrBaSiO4:Eu2+ phosphor also promotes the color performance and lumen output of WLED devices at high correlated color temperature around 8500K. This is the first time this approach is applied and it results can be utilized for better understanding of optical properties interaction with phosphor materials. Although SrBaSiO4:Eu2+ receives many positive responses, we still need to limit it concentration for high SrBaSiO4:Eu2+ concentration is detrimental to CQS. The appropriate choice of concentration and size of SrBaSiO4:Eu2+ is the principal factor to decide the performance of MCW-LEDs.

Photoluminescence properties and thermal stability of Eu3+-activated La7Ta3W4O30 red-emitting phosphors for near-UV-excited w-LEDs

Novel trivalent europium (Eu3+)-activated La7Ta3W4O30:xEu3+ (x = 0.5 mol%–40 mol%) red-emitting phosphors were synthesized by means of a high-temperature solid-state reaction. The structure, morphology, photoluminescence, thermal-stability properties, lifetime, and color-rendering of the prepared phosphors were investigated in detail. The La7Ta3W4O30:Eu3+ phosphors show five emission peaks under near-ultraviolet (n-UV) at 397 nm, and these peaks are ascribed to the transitions of 5D0–7Fj (j = 0, 1, 2, 3 and 4) by Eu3+ ions. The optimal doping concentration of Eu3+ is 20 mol%, and the critical distance of the energy transfer between the Eu3+ ions was calculated to be 1.768 nm. The quenching temperature (T0.5) of La7Ta3W4O30:20 mol%Eu3+ is about 440 K. The quantum yield (QY) was measured to be 85.85%. The fabricated white-light-emitting diodes (w-LEDs) possess high color-rendering index (Ra) of 90, and high correlated color temperature (CCT) of 5810 K, respectively. The Commission Internationale de L' Eclairage (CIE) coordinates are (0.311, 0.322). Therefore, the prepared phosphor has a promising application for w-LEDs.