Correlated Color Temperature Values Research Articles

Spectral reflectance and chromaticity differences of various colors of interior finishing material samples under tunable LED lamps

The appearance of objects in interior lighting scenarios is determined by spectral characteristics of the light sources and of the interior finishing material surfaces. Within recent developments of tunable LED lamps, it is possible to vary the correlated color temperature (CCT) of the sources; however, it is relatively unknown whether such variations shall also shift the color appearance. Therefore, this study aims to identify and to analyze the spectral reflectance and chromaticity differences of various colors of interior finishing samples under a tunable LED lamp with varying CCT. The chromaticity coordinates were estimated from the spectrally reflected exitance, under the CIE standard illuminant E and a tunable LED lamp with 10 CCT values (2000–6500 K). Ten samples of painted plywood and wallpapers of various colors were tested. Spectral reflectance of the painted plywood and wallpaper with yellow, beige, red, pink, brown colors can be accurately measured under the tunable LED with CCT 5000 K. Meanwhile, dark blue, dark green, light green, gray, light gray colors are best to be measured under CCT 5500 K. The smallest difference of chromaticity coordinate (Δu'v' = 0.117) is obtained for the light green color sample, meaning that its color appearance is the least likely to change when illuminated by LED lamp with varying CCT. The key contribution is the method to determine the characteristics of interior finishing materials with different colors, observed under tunable LED lamps. The findings can be applied as guideline to optimize objects color appearance in various interior lighting scenarios.

Er3+ ion doped low phonon energy glass as a white light emitter

White light emitters remain in the need of continual development and research for new materials. In this context, a low phonon energy glass containing Er3+ ions was prepared using the conventional melt/casting technique. The chemical compositions of the synthesized materials were analyzed using X-Ray Fluorescence (XRF) measurements. X-Ray Diffraction (XRD) pattern strongly affirms the non-crystalline essence of the produced materials. The behavior of both density and Fourier Transform Infrared (FTIR) spectroscopy denoted that the Er3+ ions have a modifier role and non-bridging oxygens NBOs were formed inside the studied glass network. The studied glasses have low phonon energy, ranging from 647 to 659 cm-1. The obtained results of the thermal, thermo-mechanical, mechanical, and optical properties were discussed in light of the structural changes brought about by inserting Er3+ ions inside the studied network. The present glasses have high thermal stability, high thermal expansion, and high refractive index. With the increase of Er3+ ion content, the Vickers microhardness VMH decreased from 3.78 GPa to 3.20 GPa. Under near ultraviolet NUV 380 nm excitation wavelength, three emission bands; blue, green, and red are observed. The white light is possible by a suitable combination of these colors. The cool white light emission was confirmed using CIE 1931 chromaticity diagram and correlated color temperature values. According to the obtained results, the studied glasses are nominated as a white light emitter in photonic applications.

Design of green emitting CaZrO3:Tb3+ nanophosphor: Luminescence based platform for real-time ultrasensitive detection of latent fingerprints and anti-counterfeiting applications

Rare earth doped phosphors are widely applied to the numerous fields, such as luminescent paints, white-light emitting devices, photovoltaics, security inks, etc., owing to their inherent properties, such as sharp emission profiles, substantial stoke shifts, and long luminescence life time. Here, green emitting CaZrO3:Tb3+ (x = 1–11 mol %) nanophosphors have been successfully prepared by solution combustion route using Cordia myxa (lasura) leaves extract as fuel. The powder X-ray diffraction patterns shows orthorhombic crystal structure. Surface morphology of the samples showed porous and flakes type with large void spaces. Photoluminescence spectra exhibits a series of sharp peaks in the wavelength range of 475–650 nm, which ascribed to 5D4→7F6-3 transitions of the Tb3+ ions. The Commission Internationale de I'Eclairage chromaticity coordinates are evaluated from the photoluminescence emission spectra and exhibited co-ordinates (0.32, 0.40) located within the plane green region of the diagram. Highest color purity was achieved for 5 mol % of Tb3+ ions doped CaZrO3 nanophosphors with an average correlated color temperature value ~6025 K. Thermoluminescence properties of the prepared nanophosphors exposed with ultraviolet light exhibit two glow peaks at ~166 and 328 °C. A linear and sub-linear responses of the thermoluminescence intensity after ultraviolet light exposure on samples confirms that the samples are more suitable for dosimetry applications. Latent fingerprints are developed using optimized CaZrO3:Tb3+(5 mol %) nanophosphor exhibit high sensitivity and selectivity, high contrast and low background interference on different surfaces. More importantly, the single information encryption strategy was designed and used for high-level anti-counterfeiting. The results clearly indicate that the optimized nanophosphor has great potential for real time applications in white light emitting diodes, dosimetry and advanced forensic applications.

Al2O3–Ce:YAG composite ceramics for high brightness lighting: Cerium doping effect

Efficient Al2O3–Ce:YAG composite ceramic phosphors were obtained via reactive vacuum sintering using commercial α-Al2O3, Y2O3, and CeO2 powders as starting materials, and SiO2, MgO as a complex sintering additive. The effect of cerium content (0.05–0.3 at%) on the structural-phase state, optical and photoluminescent properties of ceramic phosphors were investigated comprehensively by X-ray diffraction, high-resolution scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, confocal laser scanning microscopy, ultraviolet-visible spectrophotometry, and photoluminescence examinations. It is shown that an increase in the cerium doping level of the composites initiates their partial recharging into the non-luminescent Ce4+ state and the parasitic introduction of magnesium ions into the aluminum oxide phase due to the stabilization of the crystal structure of Mg,Si,Ce:YAG solid solutions. The highest value of the photoluminescence intensity is observed for the 0.1 at% Ce3+ sample, which may be caused by the optimal ratio of its absorbance and radiative recombination rate compared to other samples. The obtained ceramic phosphors show excellent thermal quenching behavior – reduction in the photoluminescence emission intensities did not exceed 5% at heating temperatures to 150 °C, which can be regarded as almost unchanged. The correlated color temperature values of 1.0 and 0.4-mm-thick Al2O3–Ce:YAG samples with 0.05–0.3 at% Ce3+ doping varied between 4583 and 3890 K and 10,308–4146 K at color rendering index values of 61–35 and 74–55, respectively. It is concluded that 0.05–0.1 at% Ce3+-doped ceramic phosphors have an optimal balance between a high color rendering index, luminous efficiency, and appropriate correlated color temperature values for high-power and high-brightness natural white light-emitting diodes.

Realization of non-rare earth doped blue-emitting phosphor Ba2Y5B5O17: Sb by selective site excitation, and its application in n-UV excited wLEDs

In this work, a new series of non-rare earth doped Ba2Y5B5O17: x at.% Sb3+ (BYBO: x at.% Sb) blue light phosphors were synthesized by high temperature solid state method. The structural analysis supported that Sb3+ can occupy four different kinds of lattice sites in BYBO crystal structure. By selecting the excitation conditions for Sb3+ ions at different lattice sites, a wide range of emission wavelength tuning exceeding 100 nm can be achieved. Our experimental results demonstrated that, by using 370 nm near-ultraviolet (n-UV) light to excite the Sb3+ ions at the Y4 (Sb1) lattice occupancy in BYBO: 3 at.% Sb, the blue light emission can be realized. White light emitting diode (wLED) was fabricated by combining 370 nm n-UV chip with purchased (Sr, Ba)2SiO4: Eu, (Sr, Ca)AlSiN3: Eu and synthesized BYBO: 3 at.% Sb phosphor. From the measured electroluminescence (EL) spectrum of the packaged wLED, the correlated color temperature (CCT) and color rendering index (CRI) were calculated to be 3816 K and 91.25, respectively. These results indicated that BYBO: 3 at.% Sb can serve as excellent blue phosphor for preparing n-UV excited wLED with low CCT and high CRI value.

Analysis of fluorescence characteristics of Sm3+-doped B2O3-rich glasses for Orange-light-emitting diodes

Optical absorption and visible luminescence aspects including visible emission decay times have been examined for six Sm3+ (1 mol%)-doped B2O3-rich glasses comprising single and mixed alkali oxides which were synthesized via melting-and-quenching approach. Upon intense λexci. = 409 nm, fluorescence spectra displayed four bands peaked at 562 nm, 598 nm, 645 nm, and 706 nm owing to 4G5/2 upper level to 6H5/2, 6H7/2, 6H9/2, and 6H11/2 lower levels transitions respectively. Among identified emissions, orange fluorescence (598 nm) is found to be strong in all samples. Moreover Sm3+: Li ions having sample exhibits the dominant visible emissions band intensity in all samples, so for this sample, Judd–Ofelt (JO) analysis was carried out to calculate JO parameters Ωt (t = 2, 4, 6), and from them, radiative transition probabilities, branching ratios (calculated and experimental), and radiative lifetimes of Sm3+: 4G5/2 level to distinct lower energy states were derived utilizing absorption and emission spectra. CIE (Commission Internationale de l′éclairage) coordinates, correlated color temperature (CCT), color purity, color rendering index, and luminous efficiency of radiation were determined from visible luminescence spectra of all studied glasses, and obtained CIE coordinates and CCT values lie in the reddish-orange light region of CIE diagram, indicating their potential for orange LEDs (light-emitting diodes) application. Here derived CCT values are lower than the typical warm light sources CCT limit (<3200 K). 4G5/2 state luminescence decay patterns revealed double exponential behavior for assessing the measured lifetimes. Effective bandwidth, stimulated emission cross-section, and gain bandwidth were computed for observed luminescence transitions of Sm3+: Li ions possessing sample.

Pr3+-doped B2O3–Bi2O3–ZnO–NaF glasses comprising alkali/mixed alkali oxides for potential warm white light generation, blue laser, and E-+S-+C-optical bands amplification applications

For six 1 mol% Pr 3+ -doped B 2 O 3 –Bi 2 O 3 –ZnO–NaF glasses consisting of single and mixed alkali oxides, optical absorption and visible and near-infrared (NIR) luminescence traits including visible fluorescence decay times were investigated. Judd–Ofelt (J‒O) analysis from absorption spectra was performed to calculate J‒O parameters Ω λ ( λ = 2, 4, 6) by including and omitting 3 H 4 → 3 P 2 transition. Utilizing Ω 2 , Ω 4 , and Ω 6 values and refractive indices, radiative transition probabilities ( A R ), branching ratios ( β R ), and radiative lifetimes for all Pr 3+ ion's luminescent levels were estimated. For observed intense blue fluorescence band upon 443 nm optical pumping, various parameters considered in designing visible laser systems were evaluated. Pr 3+ : Na + K ions comprising glass possesses large spectroscopic quality factor, high A R and β R , large stimulated emission cross-section ( σ em ), high quantum efficiency, large gain bandwidth, and significant optical gain for 3 P 0 → 3 H 4 transition for a potential blue lasing action among all samples. Further, Commission Internationale de l'éclairage (CIE) coordinates, correlated color temperature (CCT), color rendering index, and luminous efficiency of radiation were derived from visible luminescence spectra and deduced CIE and CCT values represent the neutral or warm white light region. Upon 3 H 4 → 3 P 2 excitation, NIR luminescence spectra show 3 P 1 + 1 I 6 → 1 G 4 , 1 D 2 → 3 F 4 , and 1 D 2 → 1 G 4 transitions in which broadband ( 1 D 2 → 1 G 4 ) at 1.3–1.65 μm range with effective bandwidth ~157 nm was obtained for Pr 3+ : Na + K ions constituting glass with high A R (1938 s −1 ), moderate β R (26%), and large σ em (2.64 × 10 −20 cm 2 ) at 1.472 μm, and its gain profile covers the E-+S-+C-optical communication bands' range for effective broadband amplification operation.

Advantageous Occupation of Europium(III) in the B Site of Double-Perovskite Ca2BB′O6 (B = Y, Gd, La; B′ = Sb, Nb) Frameworks for White-Light-Emitting Diodes

At present, rare-earth-activated perovskite-type materials have attracted lots of interest from researchers owing to their excellent advantages of unique electron properties and stable structure. This present work was designed to synthesize, investigate, and compare the photoluminescence properties in europium(III) (Eu³⁺)-activated Ca₂BB′O₆ (B = Y, Gd, and La; B′ = Sb and Nb) double-perovskite (A₂BB′O₆) luminescent materials. The doped Eu³⁺ ions substitute the B sites of Y³⁺, Gd³⁺, and La³⁺ ions, which are distributed to the equilibrium valence state and exhibit little difference in ion radius among them. All the resultant samples have a monoclinic structure, and the B sites strongly affect the space group in double-perovskite Ca₂BB′O₆ frameworks. Additionally, the emission intensity, thermal stability, decay curve, color purity, quantum yield (QY), etc. were determined. The Ca₂BNbO₆:Eu³⁺ (B = Y, Gd, and La) frameworks have good QYs (>42%), which are promising for white-light-emitting diodes (WLEDs). Besides, the red-emitting Ca₂BB′O₆:Eu³⁺–polydimethylsiloxane (PDMS) and white-emitting CYN0.1Eu³⁺–commercial phosphors (CP)–PDMS films were fabricated. Eventually, the packaged WLEDs based on the Ca₂BNbO₆:Eu³⁺ (B = Y, Gd, and La) powders and a novel white-emitting structure based on the CYN:0.1Eu³⁺–CP–PDMS film were confirmed to have suitable color rendering index and correlated color temperature values for indoor illumination.

Design of a novel WLED structure based on the non-rare-earth Ca2Y(Nb,Sb)O6:Mn4+ materials

Herein, the novel white light-emitting diode (WLED) structures based on the Ca2Y(Nb,Sb)O6:Mn4+ materials were presented. The crystal structure, morphology, elemental composition, luminescent behavior, thermal stability, quantum yield, decay curve, and color purity of Ca2YSbO6:Mn4+ (CYS:Mn4+) and Ca2YNbO6:Mn4+ (CYN:Mn4+) phosphors were investigated and compared in detail. For these phosphors, the concentration quenching (CQ) mechanism is different. For CYS:Mn4+ phosphors, the dipole-dipole interaction dominates the CQ while the dipole-quadrupole interaction is dominant in CYN:Mn4+ phosphors. The emission intensity of the optimal CYN:Mn4+ phosphors was stronger than that of the CYS:Mn4+ phosphors. Meanwhile, the color purities of the optimal CYS:0.003Mn4+ and CYN:0.003Mn4+ phosphors were calculated to be as high as 96.40% and 96.91%, respectively. Eventually, it is interesting that the packaged novel WLED structure would improve the color rendering index and correlated color temperature values. From the above results, non-rare-earth Ca2Y(Nb,Sb)O6:Mn4+ materials with high color purities could be proposed for WLED devices.

Energy transfer analysis and realization of cool to warm white light in Dy3+ /Sm3+ /Er3+ triply doped multicomponent borosilicate glass for white light generation.

A series of Dy3+ /Sm3+ /Er3+ triply doped multicomponent borosilicate glasses (DSE) was synthesized using varying Er3+ ions concentrations through a conventional melt quenching technique. The influence of triple doping on the optical characteristics of the prepared glass was evaluated to estimate the possibility of achieving white light emission through optical absorption, photoluminescence excitation (PLE), and emission (PL) measurements. Based on the PLE and PL spectral profiles, the presence of energy transfer processes between Dy3+ , Sm3+ , and Er3+ was confirmed. Furthermore, for Dy3+ /Sm3+ /Er3+ triply doped glass, an enhancement in Er3+ green luminescence and a noticeable decrease in Dy3+ and Sm3+ emissions were detected with the increase in Er3+ concentration. The nature of energy transfer in DSE glass was investigated through Dexter's energy transfer mechanisms and the obtained result suggested that a dipole-dipole interaction was responsible for the dominant Sm3+ to Dy3+ and Dy3+ to Er3+ energy transfer processes. The precise characteristic colours that emanated from the as-prepared samples were evaluated using Commission Internationale de l'Éclairage co-ordinates and correlated colour temperature values and suggested its suitability for white light emission. The quantum efficiency of the prepared glass was determined experimentally. The aforementioned results recommend that the Dy3+ /Sm3+ /Er3+ triply doped multicomponent borosilicate glass irradiated with ultraviolet light sources might be useful for the generation of cool/warm white light-emitting applications.

Visible to infrared emission from (Eu3+/Nd3+):B2O3 + AlF3 + NaF + CaF2 glasses for luminescent solar converters

Melt quenching technique was used for the preparation of fluoroborate (BFanc:B2O3 + AlF3 + NaF + CaF2) glasses with europium (Eu3+) and neodymium (Nd3+) ions. The absorption bands of (Eu3+/Nd3+):BFanc glasses in the visible and near infrared (NIR) regions and their spectral response with the standard solar spectrum were studied. The co-operative type down conversion (DC) process was explored using a photoluminescence (PL) spectra, which can convert a blue photon (464 nm) of Eu3+ (visible) into three photons (905, 1072, and 1346 nm) of Nd3+ (NIR) ions. The decay curves for the 615 nm (5D0→7F2) emission were fitted well to the bi-exponential function in (Eu3+/Nd3+) co-activated BFanc glasses. The faster decline of lifetime with increasing Nd3+ concentration indicates the efficient energy transfer (ET) between Eu3+ and Nd3+ ions. This ET:(Eu3+ → Nd3+) upon a dipole-quadrupole interaction was confirmed by the Dexter and Reisfeld’s theory. Moreover, quantum efficiency (ηQE) was calculated from the results of decay times, and achieved a maximum value of 185%. By stimulating with 464 nm, the color coordinates were significantly fallen in red region and their correlated color temperature values were calculated to be at around 1000 K. The aforementioned results suggest that (Eu3+/Nd3+):BFanc glasses could be used as the spectral convertors in silicon solar cells and efficient NIR emitters, and also for warm light sources.

Carbon‐Dot‐Based White‐Light‐Emitting Diodes with Adjustable Correlated Color Temperature Guided by Machine Learning

AbstractHere, we show the fabrication of the carbon dots (CDs) with green and orange emissions from PTCDA (perylene‐3,4,9,10‐tetracarboxylic dianhydride). Using these CDs as emitters, the orange (or green) CDs LEDs were fabricated, which show electroluminescence (EL) spectra centered at 560 nm (or 498 nm) with an external quantum efficiency (EQE) of 1.98 % (1.76 %) adhering a luminescence of 626 cd m−2 (or 519 cd m−2). The machine learning was successfully used to predict PL CCT value. With the model, the white photoluminescence (PL) emission with adjustable correlated color temperature (CCT) from 3093 to 11018 K via combining blue, green, and orange CDs was achieved. Then, we obtained the warm white CDs LEDs with CCT of 3107, 4071 and 4548 K, and cold white CDs LEDs with CCT of 5632 (CIE coordinates of (0.33, 0.33), EQE: 1.18 %, luminescence: 598 cd m−2) and 6034 K accurately.

Carbon-Dot-Based White-Light-Emitting Diodes with Adjustable Correlated Color Temperature Guided by Machine Learning.

Here, we show the fabrication of the carbon dots (CDs) with green and orange emissions from PTCDA (perylene-3,4,9,10-tetracarboxylic dianhydride). Using these CDs as emitters, the orange (or green) CDs LEDs were fabricated, which show electroluminescence (EL) spectra centered at 560 nm (or 498 nm) with an external quantum efficiency (EQE) of 1.98 % (1.76 %) adhering a luminescence of 626 cd m-2 (or 519 cd m-2 ). The machine learning was successfully used to predict PL CCT value. With the model, the white photoluminescence (PL) emission with adjustable correlated color temperature (CCT) from 3093 to 11018 K via combining blue, green, and orange CDs was achieved. Then, we obtained the warm white CDs LEDs with CCT of 3107, 4071 and 4548 K, and cold white CDs LEDs with CCT of 5632 (CIE coordinates of (0.33, 0.33), EQE: 1.18 %, luminescence: 598 cd m-2 ) and 6034 K accurately.

Study of the Photoluminescence Characteristics of 4,4′-((1E,1′E)-Quinoxaline-2,3-diylbis(ethene-2,1-diyl))bis(N,N-dimethylaniline)

A comparative investigation on the photophysical properties of a quinoxaline derivative 4,4'-((1E,1'E)-quinoxaline-2,3-diylbis(ethene-2,1-diyl))bis(N,N-dimethylaniline) (QDMA2) was performed by employing many spectroscopies. Based on the pump-dump/push-probe measurement, it is found that a solvent-stabilized charge-transfer state can participate in the relaxation of excited QDMA2 with increasing solvent polarity. Meanwhile, the aggregated QDMA2 molecules were engineered into the organic light-emitting diode test, which showed a correlated color temperature value of 1875 K. With the help of a diamond anvil cell, the pressure-dependent photoluminescence of aggregated QDMA2 shows that the intermolecular interaction can affect the color and intensity of photoluminescence through adjusting the band gap and irradiative channel of the aggregated molecules. These results are important for understanding the structure-property relationships and the rational design of functional materials for optoelectronic applications.

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.

Tunable luminescence and realization of warm white light via energy transfer from Dy3+/Er3+/Sm3+ triply doped glasses for photonic applications

The spectroscopic exploration of Dy 3+ /Er 3+ /Sm 3+ singly, doubly and triply doped BaO + ZnF 2 +K 2 O + SiO 2 +B 2 O 3 glasses have been carried out through photoluminescence excitation and emission, decay profiles, CIE color co-ordinates and correlated color temperature (CCT) values. Co-occurrence of Dy 3+ , Er 3+ and Sm 3+ luminescent bands in the fluorescence spectra of Dy 3+ /Er 3+ /Sm 3+ triply doped multicomponent borosilicate glasses with different excitation wavelengths (348, 374, 379 and 400 nm) emphasizes the existence of energy transfer processes and is studied in detail. The luminescence intensity of Er 3+ and Sm 3+ bands has shown a remarkable reduction with the increase in Dy 3+ content, whereas Dy 3+ bands seemed to be enhanced monotonously. Luminescent kinetics of as-prepared samples were investigated thoroughly by using recorded decay profiles and the observed decrement in lifetime values validated proposed Er 3+ (or Sm 3+ ) to Dy 3+ energy transfer routes. The energy transfer efficiency was considerably increased with the increase in concentration of Dy 3+ ions and is substantially interpreted using partial energy level diagrams. The estimated CCT values and CIE color co-ordinates of the prepared samples were significantly changed from reddish-orange to warm white light and it suggests the suitability of the material for lighting applications. • Multicomponent borosilicate glass is optically activated with Dy 3+ /Er 3+ /Sm 3+ ions. • The influence of Dy 3+ ions on the spectroscopic properties of triply doped glasses was examined. • Luminescent kinetics of as-prepared samples were investigated thoroughly by using photoluminescence decay profiles. • Energy transfer from Er 3+ (or Sm 3+ ) to Dy 3+ occurs. • Tunable luminescence was observed in the glassy system under different excitation wavelengths.

Recommendation of indoor luminous environment for occupants using big data analysis based on machine learning

To provide an optimal luminous environment for occupants, a personalized luminous environment can be recommended by analyzing personal lifelog data. A basic platform for collecting lifelog data was constructed based on a previous study, and the collected data were classified into three types: task, fatigue, and emotion. Twelve tasks were defined, and appropriate ranges of illuminance and correlated color temperature (CCT) were recommended for each task. In addition, fatigue was divided into four levels, and the most appropriate values of illuminance and CCT were specified within the ranges recommended for each task. In addition, the lighting colors that can alter or improve emotions were designated by selecting the first and second priorities among the five emotions. Totally, 31,680 luminous environment data were processed based on the collected lifelog data, which were divided into training and test datasets. A machine learning (ML)-based luminous environment recommendation system was constructed by applying four ML algorithms (K-nearest neighbor, decision tree, random forest, and support vector machine). The system was designed to recommend an occupant-customized luminous environment based on the task type, fatigue level, and emotion class, and showed an accuracy of approximately 92% or higher.

The impact of LED spectrum and correlated color temperature on driving safety in long tunnel lighting

According to the Chinese Guidelines JTG/T D70/2-01-2014, there are many long tunnels in China, especially in mountainous areas. In long tunnels, tunnel lighting influence not only visual performance but also non-visual effects. Non-visual effects has enhanced the importance of some factors directly related to driving safety, such as pupil constriction and visual fatigue which seriously affect reaction time of driver. In this work, the relationship between LED spectrum, correlated color temperature (CCT) and reaction time, pupil area difference are analyzed respectively by the experiment of reaction time. Five LEDs with different CCT and short-wave relative spectral value (RSV) are compared to HPS and MH under different tunnel lighting conditions. Experimental results show that, in the threshold and transition zone of long tunnel at luminance160cd/m2, 80 cd/m2 and 24 cd/m2, reaction time is the shortest and pupil constricted the most for LED lighting with CCT 5100 K and short-wave RSV 0.312. While in the interior zone of long tunnel at luminance 4.5 cd/m2 and 2.5 cd/m2, reaction time is the shortest and pupil constricted the most for LED lighting with CCT 3800 K and short-wave RSV 0.215. Based on the results, combining the impacts of visual performance and non-visual effects in long tunnels, this work proposed the recommended values of CCT and short-wave RSV for LED light sources that are suitable for the luminance level of different zones. In this way, the precise lighting can be implemented to meet the needs of long tunnel lighting for driving safety and energy saving.

Realization of high-quality white light emission in single-phased α-Sr2P2O7: Dy3+, Tm3+ phosphor

A single-phased white phosphor of α-Sr2P2O7: Dy3+, Tm3+ with low correlated color temperature (CCT) was synthesized by high temperature solid phase method. Our experimental results show that by co-doping Tm3+ and Dy3+ ions in the α-Sr2P2O7 matrix, the blue characteristic emission peak of Tm3+ ions can be used to effectively enhance the blue emission of the phosphor, and finally achieve high-quality white light emission. Moreover, since the emission spectrum of Tm3+ overlaps with the excitation spectrum of Dy3+ in the wavelength band from 445 to 465 nm, Tm3+ can transfer energy to Dy3+ ions, so the emission spectrum of Dy3+ can be further regulated and the emission intensity can be improved. Consequently, by optimizing the co-doping ratio of Tm3+ and Dy3+ ions, we achieved the optimal white light emission in α-Sr2P2O7: 0.01Tm3+, 0.01Dy3+ samples. Under the excitation of 351 nm ultraviolet light, the color coordinates of α-Sr2P2O7: 0.01Tm3+, 0.01Dy3+ emitting white light are (0.3292, 0.3521), and the CCT value is 5500 K, which are almost consistent with the color coordinates of standard white light and the color temperature of daylight. Therefore, α-Sr2P2O7: Dy3+, Tm3+ is a single-phased white phosphor material with great application potential for UV excitation.

Rare-earth-free Sr2YSb1-xO6:xMn4+: Synthesis, structure, luminescence behavior, thermal stability, and applications

We report the rare-earth-free Sr2YSbO6 (SYS):Mn4+ phosphors with excellent photoluminescence performance for indoor illuminations. The phase structure, elemental composition, luminescence behavior, thermal stability, lifetime, color purity, and quantum yield (QY) were analyzed in detail. The resultant sample showed a broadband excitation wavelength in the range of 250–450 nm, and the optimal doping concentration was 0.5 mol%. Under the suitable excitation wavelength of 307 nm, the SYS:0.005Mn4+ phosphor emitted a deep-red emission with the Commission Internationale de I'Eclairage chromaticity coordinate of (0.708, 0.290) and a high color purity of 93.34%. The emission intensity was found to be about 59.45% at 423 K while the activation energy was 0.28 eV. Moreover, the lifetime and QY of the optimal sample were measured to be 641.58 µs and 38.37%, respectively. Eventually, the white lighting-emitting didoes (LEDs) exhibited a strong white light with good color-rendering index (CRI) and correlated color temperature (CCT) values. Besides that, the novel LED structure based on the SYS:0.005Mn4+-polydimethylsiloxane film could also emit a warm white region while the CRI and CCT values were measured to be about 81.39 and 3091 K.