Low Color Temperature Research Articles

Ternary solid solution phosphors Ca1-x-yLixAl1-x-ySi1+x+yN3-yOy:Ce3+ with enhanced thermal stability for high-power laser lighting

The discovery of thermally robust phosphors is essential to achieve efficient and stable luminescence in solid-state lighting devices, especial in high-power devices. Here, a novel ternary solid solution phosphor enabling to address this challenge is designed by introducing isostructural LiSi2N3 and Si2N2O into CaAlSiN3 lattice. The compound, Ca1-x-yLixAl1-x-ySi1+x+yN3-yOy:Ce3+ (CALSON:Ce), exhibits an excellent thermal stability with an integrated emission loss of only 9% at 200 °C, far smaller than that of the parent CaAlSiN3:Ce3+ (25%). The enhanced thermal stability is assigned to the broadened band gap (5.21 → 5.50 eV) upon the formation of solid solutions. Moreover, the new phosphor presents a broadband (full width at half maximum of 135 nm) yellow-orange emission peaking at 580 nm and shows a high external quantum efficiency of 41.5%. The excellent photoluminescence properties and thermal stability of CALSON:Ce thus enable it to be used under high-power laser excitation, and to produce high-brightness white light having a luminous flux of 392 lm (luminous emittance of 781 lm mm−2), a low correlated color temperature of 4349 K, and a high color rendering index of 70. This work suggests that creating multi-component solid solutions would be a general strategy for designing novel phosphors.

Bright cyan-to-green color-tunable emissions from Ce3+/Tb3+ co-activated garnet phosphors for high-color-quality solid-state lighting

High-efficiency near-UV excitable inorganic phosphors with tunable emissions are highly demanded for white light-emitting diodes (LEDs) and displays. In this paper, a series of color-tunable cyan-green-emitting Ca2Lu0.99-xZr2(AlO4)3:1%Ce3+,xTb3+ (CLZA:1%Ce3+,xTb3+) phosphors was synthesized via a high-temperature solid-state reaction method. Their crystal structure, morphology, emission and excitation spectra, energy transfer properties, CIE color coordinates, internal quantum efficiency and temperature-dependent spectra were systematically researched. Impressively, these CLZA:1%Ce3+,xTb3+ phosphors showed an intense excitation band in the 370–475 nm wavelength range with a peak at 408 nm corresponding to the 4f→5d transitions of Ce3+ ions. Owing to the energy transfer from Ce3+ to Tb3+ ions, bright cyan-to-green color-tunable emissions were obtained in CLZA:1%Ce3+,xTb3+ phosphors with an increase of the Tb3+ doping concentration, and the corresponding CIE color coordinates changed from (0.156, 0.249) to (0.341, 0.533) when the Tb3+ doping concentration increased from x = 0 to 90%. The internal quantum efficiency reached up to 69%. Moreover, temperature-dependent spectra demonstrated good thermal stability and color stability of the as-prepared Ce3+/Tb3+ doped Ca2LuZr2(AlO4)3 phosphors. In addition, a white LED device was fabricated by coating the blend of the as-prepared cyan-emitting CLZA:1%Ce3+,10%Tb3+ phosphor and commercial red phosphor CaAlSiN3:Eu2+ on a 400 nm LED chip, which exhibited bright warm-white light with CIE coordinates of (0.425, 0.376), low correlated color temperature of 2,975 K and high color rendering index value of Ra = 83 and R9 = 89. These results revealed that the CLZA:Ce3+,Tb3+ phosphors could be excellent candidates for the application of near-UV-excited warm-white LEDs.

Plasmonic effects of copper nanoparticles in polymer photovoltaic devices for outdoor and indoor applications

The use of metal nanoparticles (NPs) that can trigger localized surface plasmon resonance (LSPR) is an effective method for improving the performance of organic photovoltaics (OPVs). Currently, most plasmonic NPs are based on noble metals, including gold and silver; their high cost limits their commercial applications in the cost-effective OPVs. Herein, copper (Cu) NPs, which are more abundant and cheaper, are adopted to fabricate OPVs. To avoid oxidation of Cu NPs, they are positioned at the cathode interface, so that their fabrication could be implemented in an inert environment. The resulting OPVs exhibited improved power conversion efficiencies (PCEs) under illumination at 1 sun, and the device enhancement could be attributed to the LSPR effects of Cu NPs. Further, their potential to enhance the performance of OPVs under indoor lighting conditions is evaluated. The enhancement factor of PCEs was higher, while the light source had a lower color temperature. It could be due to the fact that the main plasmonic band of the Cu NPs is localized in the red spectral range. The results reveal the consideration of matching between the LSPR spectral range and the emission spectra of the artificial light sources is very critical for indoor applications.

High-Brightness Red-Emitting Phosphor La3(Si,Al)6(O,N)11:Ce3+ for Next-Generation Solid-State Light Sources.

A novel high-brightness red-emitting phosphor, La3(Si,Al)6(O,N)11:Ce3+ (LSA), which can potentially be used as a laser-excited light source, is demonstrated. Laser-excited phosphor system has great potential for use as a white-light source, as it is orders of magnitude brighter than white LEDs. Although conventional yellow-green phosphors show excellent luminescent properties even under high-power laser excitation, red-emitting phosphors, which are essential to achieve a high color-rendering index and low color-temperature, show quantum efficiency quenching. This limits the output power in multiphosphor excitation systems. Ce3+ should successfully tolerate high-power excitation due to the shortest emission lifetime seen in rare-earth ions, caused by the 5d1-4f1 spin-allowed transition; however, a red-emitting Ce3+-doped phosphor of practical use has not been realized. LSA is described by the crystal-field modification of a yellow-emitting phosphor, La3Si6N11:Ce3+, with substitution of Al in Si sites. LSA shows 640 nm red emission together with tolerance for high-power excitation and thermal quenching, suggesting its significant potential for industrial applications that require ultrahigh brightness.

Engineering mixed polyanion red-emitting Rb2Bi(PO4)(WO4):Eu3+ phosphors with negligible thermal quenching and high quantum yield

The high-performance red-emitting phosphors are strongly demanded as the next generation solid state lighting materials. Benefitting from the favorable accommodation capacity of polyanions and high charge transfer energy state in the structure, the pure red-emitting Rb2Bi(PO4)(WO4):Eu3+ (RBPWO:Eu3+) materials with negligible thermal quenching and high quantum yield were synthesized. RBPWO:Eu3+ has high absolute quantum yields of 88.1% and exceptional thermal stability of 98.6% integral retention at 423 K relative to the initial value at 298 K. Additionally, affected by the low symmetry crystalline-field of D2h, the title phosphors exhibit intense absorption band peaking at 394 nm and pure red light with the color CIE values (0.6482, 0.3515). The white light-emitting diode (w-LED) device fabricated from the title material exhibits low correlated color temperature (4000 K), high color rendering index (Ra = 90) and moderate luminous efficiency (18.07 lm/W) in the preliminary experiment. The present work indicates that the RBPWO:Eu3+ phosphors are promising red components for the near ultraviolet light excited w-LEDs.

A red phosphor LaSc3(BO3)4:Eu3+ with zero-thermal-quenching and high quantum efficiency for LEDs

A novel red phosphor LaSc3(BO3)4:Eu3+ with high quantum efficiency and zero-thermal-quenching was reported. The crystal structure and electronic structure were investigated by Rietveld refinement method and density functional theory (DFT) calculations. The FE-SEM and TEM analysis were performed to further understand the phase evolution of LaSc3(BO3)4:Eu3+. The energy migration among Eu3+ ions was strongly suppressed due to the long distance of nearest-neighbor Eu3+ sites. The phosphor exhibited high doping concentration of 80 mol%, high quantum efficiency of 88.3% and zero-thermal-quenching until 275 °C. Further researches show that the zero-thermal-quenching behavior is consistent with the thermal disturbance model. Finally, A warm white light LED device with a low correlated color temperature (CCT) of 3438 K and high color rendering index (CRI) of 92.5 was fabricated based on the as-prepared red phosphor LaSc3(BO3)4:Eu3+, indicating that LaSc3(BO3)4:Eu3+phosphor is promising for high-power LEDs. These findings may open up new ways for the exploration of high-performance Eu3+-activated phosphors.

Synthesis of Silica-Coated Cs4PbBr6 and Cs4Pb(Br0.4I0.6)6 Quantum Dots With Long Lifetime and Enhancement in Quantum Efficiency for WLEDs Applications: Lightings With High CRI and Displays With Wide Color Gamut

To focus on developing white light-emitting diodes (WLEDs) for lightings with high color rendering index (CRI), low correlated color temperature (CCT), and the displays with wide color gamut, inorganic perovskite quantum dots (QDs) such as CsPbX3 (X = C1, Br, I) were the promising candidate owing to the excellent optoelectronic properties such as high quantum efficiency, narrow emission wavelengths, and tunable emission spectrum. Nevertheless, the CsPbBr3QDs in the form of powders or films had a poor air stability and severe decline of quantum efficiency. Therefore, in this article, a new idea was proposed that 0-D green–red perovskite QDs powders such as Cs4PbBr6 and Cs4Pb(Br0.4I0.6)6 with improved quantum efficiency and long lifetime were first developed by silica-coated method and crystal phase transition in low-temperature synthesis. The quantum efficiency in green Cs4PbBr6 powders could be significantly enhanced from 31.41% to 45.87% and red Cs4Pb(Br0.4I0.6)6 powders was 22.79%. Moreover, the as-prepared perovskite QD powders and commercial YAG phosphors combined with blue chips were applied to high-quality WLEDs for lightings and displays. More importantly, the as-fabricated wide Commission Internationale de l’Eclairage (CIE) color gamut WLEDs for displays possessed 115% National Television System Committee (NTSC) coverage rate and luminous efficiency of 51 lm/W under 20-mA driving current. On the other hand, the constructed WLEDs for high-power lightings would generate a warm white light with a luminous efficiency of 38 lm/W, extremely high CRI of 92.8, and low CCT of 3828 K under 350 mA. Hence, the proposed green–red perovskite QD powders had outstanding potential applications in WLEDs.

Eu3+-activated Ca2YTaO6 double-perovskite compound: A novel highly efficient red-emitting phosphor for near-UV-excited warm w-LEDs

In this work, novel Eu3+ ions activated red emitting Ca2YTaO6 (CYT) phosphors have been prepared via a high-temperature solid-state reaction approach. Their crystal structure and photoluminescence properties were investigated by X-ray diffraction (XRD) patterns, photoluminescence excitation and emission spectra, and decay lifetimes. XRD Rietveld refinement results revealed that the CYT:Eu3+ phosphors crystallized in the monoclinic structure with the space group of P21/n and lattice parameters of a = 5.5989 Å, b = 5.8449 Å, c = 8.1016 Å, α = γ = 90°, β = 89.8799°, and V = 264.625 Å3. The CYT:xEu3+ phosphors could be excited by near-ultraviolet light around 396 nm, and they showed bright narrowband red emissions peaking at 590, 614, 656, and 703 nm due to the 5D0→7FJ (J = 1–4) transitions of Eu3+ ions. The 614 nm red emission corresponding to the 5D0→7F2 transition was dominant in the emission spectra, indicating that the Eu3+ ions occupied non-centrosymmetric sites. The critical quenching concentration in CYT:xEu3+ phosphors was 50 mol%, and the optimal CYT:0.5Eu3+ phosphors showed PL intensity as great as 4.2 times higher than the commercial red phosphors Y2O3:Eu3+. CIE chromaticity coordinates of CYT:0.5Eu3+ phosphors were (0.6678, 0.3319), and the color purity reached up to 97.4%. The nonradiative energy transfer between the Eu3+ ions in the CYT host was attributable to dipole-dipole interaction, and the critical distance was roughly 7.97 Å. A warm white light-emitting diode (w-LED) based on the combination of a 395 nm LED chip with a blend of commercial BaMgAl10O17:Eu2+blue phosphors and commercial (Ba,Sr)2SiO4:Eu2+ green phosphors and as-prepared CYT:0.5Eu3+ red phosphors was fabricated, which gave warm white-light emission with excellent CIE color coordinates of (0.3833, 0.3859), low correlated color temperature of 3991 K, high color rendering index of 92.1, and good luminous efficacy of 21.76 lm/W.

High performance non-doped blue-hazard-free hybrid white organic light-emitting diodes with stable high color rendering index and low efficiency roll-off

White organic light-emitting diodes (WOLEDs), for display and lighting applications, combine features such as high performance, high color quality, low efficiency roll-off and blue-hazard-free are extremely important. In this study, we manufactured a highly efficient bluish-green thermally activated delayed fluorescence (TADF) OLED. The maximum external quantum efficiency (EQE), power efficiency (PE), and current efficiency (CE) were 16.0%, 46.2 lm/W, and 45.9 cd/A, respectively. Next, a non-doped and blue-hazard-free hybrid WOLED was prepared by employing reasonably inserting several red and yellow ultra-thin phosphorescent emitters in between the bluish-green TADF emitters. The device showed a maximum EQE of 18.7% and a low EQE roll-off of 7%. At 1000 cd/m2, a high color rendering index (CRI) of 87 and a low correlated color temperature (CCT) of 2759 were obtained. The result showed that bluish-green TADF material has potential applications in healthy WOLEDs without blue-hazard. Also, the strategy of inserting several long-wavelength ultra-thin phosphorescent emitters in between bluish-green TADF emitters with bipolar transport characteristic, which can reduce efficiency roll-off and enhance device electroluminescence efficiency, was demonstrated.

Double perovskite Ca2MgTeO6:Eu3+ red-emitting phosphors with high thermal stability for near UV/blue excited white LEDs

A series of Eu3+-doped double perovskite Ca2MgTeO6 (CMTO) red-emitting phosphors with high thermal stability were successfully prepared using the solid-state reaction at 1100 °C. The phase purity, surface morphology, and elemental mapping were investigated. Under near-ultraviolet (n-UV) (398 nm) and blue light (465 nm) excitation, the phosphors showed the strongest emission peak at 616 nm belonging to 5D0→7F2 transition. Besides, the ideal Eu3+ doping concentration was 0.30 mol. The major reason for the concentration quenching was the nearest neighbor ions interaction. More importantly, the CMTO:Eu3+ phosphors showed excellent thermal stability with a high value of activation energy (0.29 eV). The color purity of CMTO:0.30Eu3+ phosphor was up to 99.9% and the internal quantum efficiency (IQE) of CMTO:0.30Eu3+ was measured to be 53%. White light-emitting diodes (w-LEDs) based on the InGaN chip (λ = 398 nm) and GaN chip (λ = 465 nm) with high color rendering index (Ra) and low correlated color temperature (CCT) have been fabricated. Hence, the double perovskite CMTO:Eu3+ red phosphors have potential applications in the illumination field.

A novel Mn4+-activated Li3CsGe8O18 red phosphor and cation substitution induced photoluminescence improvement

Nowadays, non-rare-earth Mn4+-activated red phosphors have emerged for improvement of the lighting quality of phosphor-converted white light-emitting-diodes (pc-WLED), owing to the low cost and the admirable luminescence properties. In this work, a novel narrow-band red-emitting Li3CsGe8O18:Mn4+ phosphor was synthetized based on the component substitution from Li3RbGe8O18, which exhibits the red luminescence centered at 668 nm upon 466 nm excitation. By further designing [Cs+-Rb+] cation substitution, the photoluminescence intensity and luminescence efficiency are obviously improved. The photoluminescence intensity enhanced 1.75 times than Li3RbGe8O18:Mn4+ phosphor, while the corresponding internal quantum efficiency (IQE) increased by 1.57 times. According to the Rietveld refinement results, the corresponding mechanism of luminescence enhancement is attributed to the smaller distortion degree of the [Ge(1)O6] octahedron. The pc-WLED device is fabricated by the optimal Li3Cs0.5Rb0.5Ge8O18:1%Mn4+ red phosphor, yellow phosphor with Y3Al5O12:Ce3+ and 460 nm InGaN chip, showing a warm white light emission with low correlated color temperature (4474K) and high color rendering index (90.8). The result implies that the Li3Cs0.5Rb0.5Ge8O18:1%Mn4+ phosphor can be used as a potential red phosphor for pc-WLED application.

Violet-light-excitable super-narrow band green emitting phosphor for high-quality white LEDs

Violet-light-based (390–420 nm) white LEDs are emerging as high-quality lighting devices for indoor lighting and more vivid display, in which the use of narrow-band phosphors would be beneficial for the improvement of maximum accessible color gamut, color rendering index (CRI) and visual luminous efficiency (LE). The nature of 4f electronic configuration of Tb3+ ion enables efficiently narrow-band green emission but suffering from inefficient light absorption in violet light region. Here, violet-light-excitable Tb3+ luminescence is realized in Ce3+-doped garnet Ca2TbZr2Al3O12 (CTZA) via efficient energy transfer (ET) from Ce3+ to Tb3+, providing dominant green emission originating from 5D4-7F5 transition with super-narrow full width at half maximum (FWHM) of only 9.74 nm and high internal quantum yield (QY = 60%). The performance of the white LEDs using CTZA:Ce3+ is studied, showing high CRI of 90.1, low correlated color temperature (CCT) of 3686 K and a wide color gamut of 61% of National Television System Committee standard (NTSC) in Commission Internationale de L'Eclairage (CIE) 1931 color space, which suggests its great potential for violet-based white LEDs.

Highly Efficient Cyan-Green Emission in Self-Activated Rb3RV2O8 (R = Y, Lu) Vanadate Phosphors for Full-Spectrum White Light-Emitting Diodes (LEDs).

Phosphor-converted white-light-emitting diodes (pc-WLEDs) rely on combining a near-ultraviolet (n-UV) or blue chip with trichromatic and yellow-emitting phosphors. It is challenging to discover cyan-green-emitting (480-520 nm) phosphors for compensating the spectral gap and producing full-spectrum white light. In this work, we successfully discovered two unprecedented bright cyan-green emitting Rb3RV2O8 (R = Y, Lu) phosphors that gives emission bands centered at 500 nm upon 362 nm n-UV light excitation. Interestingly, the both self-activated compounds exhibit high internal quantum efficiencies (IQEs) of 71% for Rb3YV2O8 and 85% for Rb3LuV2O8, respectively. Moreover, controllable emission color can be successfully tuned from cyan-green to orange-red across the warm white light region by design strategy of VO43- → Eu3+ energy transfer. The thermal quenching of as-prepared phosphors could be effectively mitigated by this design strategy. Finally, the as-fabricated n-UV (λex = 370 nm) pumped phosphor-converted (pc) W-LED devices utilizing Rb3RV2O8 (R = Y, Lu) along with commercial phosphors demonstrate well-distributed warm white light with high color-rendering index (CRI) of 91.9 and 93.5, and a low correlated color temperature (CCT) of 5095 and 4946 K. It suggests that the both vanadate phosphors have potential applications in full-spectrum pc-WLEDs.

Double sites occupancy of Mn4+ in Cs2NaAlF6 with enhanced photoluminescence for white light-emitting diodes

In this work, we present a novel single-phase red phosphor of Cs2NaAlF6:Mn4+ with two Al3+ lattice sites, which shows two groups of vibrational phonon sidebands and ultra-intense zero phonon line (ZPL) under blue light illumination. The evidences have shown that the interesting spectral features originate from the non-equivalent occupation of Mn4+ for both Al3+ sites, which induces the neighboring cation vacancies surrounding Mn4+ and highly distorted [MnF6] octahedral in the Cs2NaAlF6 host. The luminescent behavior of double sites occupied by Mn4+ can absorb researchers’ interest on novel red-emitting phosphors. Profiting from the photoluminescence (PL) features, superior color rendering index of Ra = 90.3, R9 = 81, and low correlated color temperature of Tc = 3967 K are achieved from white light-emitting diode (LED) by using yellow Y3Al5O12:Ce3+ (YAG) and red Cs2NaAlF6:Mn4+ phosphors as blue light converters. These results suggest that Cs2NaAlF6:Mn4+ for phosphor has a stupendous potential for LED lighting.

Eu3+-activated Ca3Mo0.2W0.8O6 red-emitting phosphors: A near-ultraviolet and blue light excitable platform for solid-state lighting and thermometer

Eu3+-activated Ca3Mo0.2W0.8O6 phosphors, which presented bright red emissions mainly from the 5D0 → 7F2 transition of Eu3+ ions upon the near-ultraviolet and blue light excitation, were successfully prepared by a traditional high-temperature technology. The crystal structure, phase constitution, morphology, electronic structure, photoluminescent behaviors, decay time, internal quantum efficiency and thermal stability of the resultant phosphors were investigated in detail. Under the excitation of 365, 393 and 465 nm, the optimal doping concentration was 9 mol% and the electrical multipolar interaction contributed to the non-radiative energy transfer between Eu3+ ions in Ca3Mo0.2W0.8O6 host lattices. Additionally, through using the prepared compounds, commercial blue/green-emitting phosphors and light-emitting diodes (LEDs), the fabricated white-LEDs emitted warm white light with excellent performance, such as good CIE coordinates, high color rending index and low correlated color temperature, when driven by 30 mA of injection current. Ultimately, according to the response of the decay time to the temperature, the thermometric performances of the resultant phosphors in the temperature range of 298–573 K were studied. The maximum sensor sensitivity of the studied phosphors reached up to 1.16% K−1 at 523 K. These achievements revealed that Eu3+-activated Ca3Mo0.2W0.8O6 phosphors were promising candidates for solid-state lighting and thermometer.

The Influence of Classroom Illumination Environment on the Efficiency of Foreign Language Learning

This paper investigated foreign language learning efficiency in four different illumination environments (in different illuminance and color temperatures), focusing on the influence of the illumination environment on foreign language learners’ sentimental status, by means of foreign language skills testing in mind-map, objective evaluation of physiological reaction, and subjective evaluation of psychological reaction. It was shown that in different illumination environments, the language skills of foreign language learners were different, and their psychological and physiological reactions varied, which influenced the efficiency of foreign language learning. The results indicated that the ideal learning space was in high illuminance and low color temperature, which increased the stimulation in foreign language learners; promoted the formation of optimistic sentiment; and enhanced their interest in, and the quality and efficiency of, foreign language learning.

Strategies for Designing Antithermal-Quenching Red Phosphors.

Nowadays, red phosphor plays a key role in improving the lighting quality and color rendering index of phosphor‐converted white light emitting diodes (w‐LEDs). However, the development of thermally stable and highly efficient red phosphor is still a pivotal challenge. Herein, a new strategy to design antithermal‐quenching red emission in Eu3+, Mn4+‐codoped phosphors is proposed. The photoluminescence intensity of Mg3Y2(1− y )Ge3O12:yEu3+, Mn4+ (0 ≤ y ≤ 1) phosphors continuously enhances with rising temperature from 298 to 523 K based on Eu3+ → Mn4+ energy transfer. For Mg3Eu2Ge3O12:Mn4+ sample, the integrated intensity at 523 K remarkably reaches 120% of that at 298 K. Interestingly, through codoping Eu3+ and Mn4+ in Mg3Y2Ge3O12, the photoluminescence color is controllably tuned from orangish‐red (610 nm) to deep‐red (660 nm) light by changing Eu3+ concentration. The fabricated w‐LEDs exhibit superior warm white light with low corrected color temperature (CCT = 4848 K) and high color rendering index (R a = 96.2), indicating the promising red component for w‐LED applications. Based on the abnormal increase in antistokes peaks of Mn4+ with temperatures, Mg3Eu2Ge3O12:Mn4+ phosphor also presents a potential application in optical thermometry sensors. This work initiates a new insight to construct thermally stable and spectra‐tunable red phosphors for various optical applications.

The Impact of LED Color Rendering on the Dark Adaptation of Human Eyes at Tunnel Entrances.

The dark adaptation of drivers’ eyes at a tunnel entrance seriously affects traffic safety. This can be improved by the design of tunnel lighting. Light-Emitting Diode (LEDs) have been applied as a new type of luminaire in tunnel lighting in recent years, but at present, there are few studies on the influence of color rendering of LEDs on tunnel traffic safety, and there is no explicit indicator for the selection of appropriate color rendering parameters in tunnel lighting specifications, which has aroused researchers’ concern. In this article, several new color rendering evaluation indexes were compared, and as a result, it is considered that CRI2012 (a color difference-based color rendering index) is more suitable for evaluating the color rendering of LEDs used at tunnel entrances. The dark adaptation phenomenon was simulated in the laboratory. Four CRI2012s, three color temperatures and eight colored targets were used in the experiments. The results showed that yellow, silver and white can provide shorter reaction times, while red and brown lead to longer reaction times, which can provide a reference for the design of road and warning signs at tunnel entrances. The effect of target color on reaction time was greater than that of color rendering. Under most target colors, the higher the CRI2012, the shorter the reaction time. When designing the color rendering of the LEDs at a tunnel entrance, the value should thus be as large as possible (close to 100), and a lower color temperature value (about 2800 K) should be selected. This paper provides technical support for tunnel lighting design and a reference for tunnel lighting specifications, which is of significance to improve driving safety and avoid traffic accidents in highway tunnels.

Tunable Photoluminescence and Energy Transfer Efficiency in β-Ca3(PO4)2-Ca9La(PO4)7:Eu2+, Mn2+ Solid Solution Phosphors Introduced by Emptying Site and Structural Confinement Effect for Solid-State Lighting Application.

Full visible emission achieved by a single-phased system is of great interest to researchers for the development of high-quality solid-state lighting devices. Herein, novel Eu2+ and Mn2+ co-doped (1 - x)β-Ca3(PO4)2-xCa9La(PO4)7 solid solution phosphors are designed to realize single-phased white light emission. The effects of variational x on lattice structure, color-tunable emission, thermal stability, and energy-transfer efficiency from Eu2+ to Mn2+ are systematically investigated. Tunable color emissions are achieved by manipulating the redistributions of Eu2+ ions among the different cationic sites under the influence of generated empty site in the M(4) site. Meanwhile, the changes of critical distances among the Eu2+ and Mn2+ caused by the variational x results in the changes of energy-transfer efficiency from different Eu2+ luminescent centers to Mn2+ due to the existence of structural confinement effect. The calculated results indicate that Eu1-Mn and Eu2-Mn possess higher energy-transfer efficiencies than other Eu-Mn pairs. Under the combined influence of the two effects, single-phased full visible white emission covering from 400 to 700 nm has been realized via the adjustment of solid solution, which makes the fabricated white-light-emitting diode (WLED) possess high color-rendering index (86.9) and R9 (87.2) as well as low correlated color temperature (3947 K). The results show that the 0.2β-Ca3(PO4)2-0.8Ca9La(PO4)7:0.01Eu2+, 0.20Mn2+ could act as a promising phosphor for single-phased WLEDs. This work will open up a new avenue for tuning the multiple activator sites and energy-transfer efficiencies simultaneously to realize single-phased full visible white emission.

Strong Narrow Red Emission in a Perturbed Fergusonite System: Y3Mg2Nb3O14:Eu3+ for White LED Applications

A series of intense red-emission phosphors, Y3Mg2Nb3O14:Eu3+, with higher color purity were prepared via the conventional high-temperature ceramic route. The influence of Mg2+ ion incorporation in the highly symmetrical YNbO4 lattice on the luminescence properties was studied using powder x-ray diffraction, scanning electron microscopy with energy dispersive spectrometry, UV–visible absorption spectroscopy, and photoluminescence measurements. The developed phosphors crystallize into a monoclinic fergusonite-type structure with a C2/c space group even with the addition of Mg into the system. These phosphors display intense, sharp, red emission with a maximum at 613 nm under near-UV excitation. The photoluminescence studies suggest that Mg addition perturbs the A site network forming cation pairs of Eu3+-Y3+, Eu3+-Mg2+, and Eu3+-Eu3+ connected with O2− ions. The preferential occupation of cations in the A site network by the incorporation of Mg2+ ions in the YNbO4 host lattice induces Eu3+-Eu3+ separation and results in intense, sharp, red emission due to increased radiative probabilities. Moreover, the color purity of the Y3−xMg2Nb3O14:xEu3+ phosphor could achieve 92.4% that is attributed to the narrow full width at half maximum (FWHM ∼ 4 nm) of the red emission peaking at 613 nm. More importantly, the luminescence intensity of the developed phosphor is 9.4 times greater than that of the Philip’s red phosphor under near-UV excitation. Because of the intriguing red luminescence, phosphors exhibit Commission Internationale de l’Elcairage color coordinates (0.63, 0.35) close to the National Television System Committee standards, low correlated color temperature values for warm white lighting, and greater color purity (92.4%) for improving the color rendering index, which makes them a potential candidate for use in the fabrication of white light-emitting diodes.