Commission Internationale De l'Eclairage Chromaticity Research Articles

Yellowish light emitting Dy3+ doped single phase – BaNb2O6 phosphors for solid state lighting applications

BaNb2O6:Dy3+ phosphors that emit cool light has been synthesized via traditional solid-state reaction technique. Developed samples show orthorhombic structure with space group C2221 according to X-Ray Diffraction (XRD) and Rietveld structural refinement. Observations made using a scanning electron microscope (SEM) show densely packed particles with irregular shapes in the micrometre range. Optical bandgap was also determined using Diffuse Reflectance Spectroscopy (DRS). When excited at 389 nm, the as-prepared phosphors show blue (481 nm) and yellow (577 nm) emissions, which correspond to the 4F9/2 → 6HJ (J = 15/2, 13/2) transitions of Dy3+ ions. A thorough investigation has been done on the energy transfer process between Dy3+ ions. The optimized phosphor's computed chromaticity coordinates for the Commission Internationale de L'Eclairage (CIE) are x = 0.392 and y = 0.414. The values of CIE chromaticity coordinates and correlated colour temperature (CCT) of 3995 K endorse near cool light emission from the phosphor. Thermal stability and temperature dependent photoluminescence spectroscopy were studied for optimized phosphor which revealed that the phosphor can be a potential material for lighting applications at higher temperature. The study also reveals that BaNb2O6:Dy3+ phosphor could be a promising candidate for near ultra-violet (NUV) excited, yellowish LED applications.

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

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

High-quality reddish-orange-emitting Sr6Y2Al4O15:Eu3+ phosphors for solid-state lighting and anti-counterfeiting applications

The reddish-orange emitting Sr6Y2Al4O15:Eu3+ phosphors were synthesized via a high-temperature solid-state reaction technique, and their luminescent properties were systematically studied. The dominant emission peak assigned to the electric dipole transition (5D0 → 7F2) was recorded at 612 nm owing to the non-inversion symmetry of the substituted sites of Eu3+ ions under the excitation of charge transfer band (∼261 nm). The emission of Sr6Y2Al4O15:Eu3+ revealed a Commission Internationale de l'Eclairage (CIE) chromaticity coordinate of (0.571, 0.368) and a color purity of 93.6 %. The thermal stability and photoluminescence quantum yield (PLQY) of Sr6Y2Al4O15: Eu3+ were analyzed, exhibiting a high thermal stability of 88.24 % at 423K and a good external PLQY of 36.24 %. Furthermore, the solid-state lighting (SSL) and flexible anti-counterfeiting applications of Sr6Y2Al4O15:Eu3+ were demonstrated. The red light-emitting diode (LED) was packaged with ∼260 nm ultraviolet LED chip, representing a CIE chromaticity coordinate of (0.5955, 0.3592) and a color purity of 86.53 %. The flexible anti-counterfeiting film was fabricated with polydimethylsiloxane polymer, and it showed tunable emission under different excitations. Moreover, the anti-counterfeiting ink was prepared and printed on various substrates. Consequently, the reddish-orange emitting Sr6Y2Al4O15: Eu3+ phosphors with high color purity, good thermal stability, and high quantum efficiency were introduced and potentially used in SSL and flexible anti-counterfeiting applications.

Structural and luminescence property evaluation of Sm3+ activated orange light emitting Li7La3Zr2O12 phosphors

• Synthesis of cubic blue light emitting pure LLZO and orange light emitting LLZO: xSm 3+ (x=0.1, 0.3, 0.5, 0.7 and 0.9 M.W%) phosphors by solid state reaction method. • The optical energy band gap values of synthesised phosphors for pure and Sm 3+ doped LLZO were calculated to be 4.140 eV and 3.972 eV, respectively. • The strongest PL emission band observed at 602 nm was assigned to 4 G 5/2 → 6 H 7/2 transition in orange region under the ultraviolet excitation wavelength of 408 nm. • The blue and orange light emission was confirmed by CIE chromaticity X, Y coordinates. • Color purity and CCT value of 0.5 MW% Sm 3+ doped LLZO phosphor was 85.9% and 2227 K, respectively. Samarium (Sm) activated Li 7 La 3 Zr 2 O 12 (LLZO) phosphors were synthesized by solid state reaction method. Crystal structure of Sm 3+ doped LLZO was investigated using X-ray diffraction and Raman spectroscopy analysis. From Raman spectra, the presence of characteristic Raman peak at 110 cm -1 confirms the formation of LLZO. The Raman peaks present at 345 cm -1 and 125 cm -1 correspond to T 2g Raman mode of vibration and E g mode of vibration, respectively. The optical energy band gap values of synthesised phosphors obtained from UV-Vis spectroscopy for pure and Sm 3+ doped LLZO were calculated to be 4.140 eV and 3.972 eV, respectively. Microstructure and selected area diffraction (SAED) pattern of phosphor was observed by High Resolution Transmission Emission Electron Microscope. Using an excitation wave length of 209 nm,blue emission was observed for pure LLZO and the chromaticity coordinate was found to be at (x=0.1636, y=0.0123). Sm 3+ doped phosphors showed orange light emission under 408 nm excitation due to transition of 4 G 5/2 - 6 H 7/2. as observed from the Commission Internationale de l’Eclairage (CIE) chromatic coordinate graph. The maximum intensity of emission was observed in 0.5% Sm 3+ doped LLZO with the calculated color purity and correlated color temperature of 85.9% and 2229k, respectively.

Triphenylamine-styryl-anthracene derivative without thermal fluorescence quenching property for spectrally stable organic/inorganic hybrid light emitting diodes with no UV residue

Herein, the organic blue emitting material (E)-4-(4-(anthracen-9-yl)styryl)-N,N-diphenylaniline (AnStDPA) with D–π–A chromophore was synthesized. The thermal, optical, electrochemical properties and the device performance of the AnStDPA were investigated. The AnStDPA shows high thermal stability with decomposition temperature (Td, 5% weight loss) value of 319 °C, high photoluminescence quantum yield (PLQY) with value of 0.92 and no thermal fluorescence quenching property. The HOMO and LUMO level of AnStDPA are −5.44 eV and −2.60 eV, respectively. When using AnStDPA to construct organic/inorganic hybrid LED, the LED exhibits blue emission, stable Commission Internationale de L'Eclairage (CIE) chromaticity coordinate of (0.1522,0.0895) and tranquil luminance efficiency of 10 lm W−1 (around) at various currents. In addition, the phosphor-free hybrid WLEDs based on AnStDPA and Rubrene (5,6,11,12-tetraphenylnaphthacene) were prepared. The device possesses luminance efficiency of 27.70 lm W−1 (at 19.90 mA), CCT of 4363 K, Ra of 65.2, and CIE chromaticity coordinate of (0.3471, 0.2750). Moreover, there is almost no ultraviolet (UV) residue in these hybrid LEDs based on the AnStDPA. We have simultaneously achieved organic/inorganic hybrid blue LED (based on near UV chip) with almost no UV residue and spectral stability.

In situ preparation and photophysical properties of a novel europium complex

Under hydrothermal conditions, a novel europium complex [Eu(H2O)2 (Me-IN)3]n·2nH2O·3nClO4 (1; Me ​= ​methyl; IN ​= ​isonicotinic acid) was synthesized in situ and characterized. Complex 1 crystallizes in the monoclinic space group P21/c with four formula units in one cell. Complex 1 is characterized by a one-dimensional (1-D) chain-like structure. The solid state photoluminescence emission is in the red region and the emission peaks should come from the 5D0 → 7F1, 5D0 → 7F2 and 5D0 → 7F4 characteristic emission of the Eu(III) ions. It has a CIE (Commission Internationale de L’Eclairage) chromaticity coordinates of (0.5442, 0.4444). A solid-state UV–visible diffuse reflectance spectrum unveiled that it possesses a wide optical band gap of 4.98 ​eV.

Photoluminescence properties and energy transfer of novel orange–red emitting phosphors: Ba3Bi2(PO4)4: Sm3+, Eu3+ for white light-emitting diodes

Sm3+, Eu3+ co-coped Ba3Bi2(PO4)4 phosphors, as potential phosphors for white light-emitting diode applications, were synthesized through the solid-state reaction method for the first time. The crystal structure, absorption spectra, photoluminescence properties, decay time, energy transfer mechanism, temperature-dependent properties, and Commission International De L’Eclairage (CIE) chromaticity coordinates were investigated systematically. The pure eulytite-type Ba3Bi2(PO4)4 phase was obtained after heating at 980 °C for 5 h. A notably enhanced absorption efficiency at 393 nm was observed when Sm3+, as a sensitizer, was doped into Ba3Bi1.82(PO4)4: 0.18Eu3+ and the band gap of the Ba3Bi2(PO4)4 host was estimated to be 4.19 eV. The emission intensity of Ba3Bi1.82(PO4)4: 0.18Eu3+ was significantly enhanced when Sm3+ was co-doped. The existence and mechanism of energy transfer from Sm3+ to Eu3+ were evaluated by photoluminescence spectra and decay time measurements. The CIE chromaticity coordinate of Ba3Bi1.75(PO4)4: 0.07Sm3+, 0.18Eu3+ phosphor was calculated to be (0.5746, 0.4197), respectively.

Structural and spectroscopic characteristics of Eu3+ embedded titanium lead phosphate glasses for red luminescence

A series of Eu3+ incorporated titanium lead phosphate glasses with the chemical compositions of 1 mol% Eu2O3+ xTiO2+(50–x)PbO+49P2O5 (where x = 1, 3 and 5) have been prepared by the melt quenching procedure. Structural investigations have been performed through XRD and FTIR spectra. Optical properties are investigated by absorption, excitation, photoluminescence emission, decay lifetime and CIE chromaticity measurements. Using absorption transition from 7F0 and 7F1 levels, the nephelauxetic ratio (β) and bonding parameter (δ) are estimated to determine the type of bonding between Eu3+ ions and the surrounding ligands. The absorption as well as the excitation spectra show that the band at 393 nm corresponding to 7F0 → 5L6 transition is very strong. Upon excitation at 393 nm, Eu3+ embedded titanium lead phosphate glasses exhibit maximum emission intensity for 5D0 → 7F2 transition at 611 nm which emits red color. Using Judd-Ofelt (JO) theory, the JO parameters Ω2, Ω4 and Ω6 have been estimated from the absorption and these parameters follow the trend of Ω2>Ω4>Ω6 for all glasses. These JO parameters are used to predict the branching ratio (βR), radiative transition probability (AR), stimulated emission cross-section (σPE) and radiative lifetime (τR). The larger value of spontaneous emission cross-section, suggests that the present glass samples are encouraging materials for Eu3+ embedded optical amplifiers and laser materials. Using the decay profile which shows single exponential, the luminescence decay lifetime of Eu3+ ions for the 5D0 metastable state is evaluated. The fluorescence quantum efficiencies have been evaluated which indicate that the values may be enhanced with the increase of titanium dioxide (TiO2) in the glass matrix. The color purity (CP) of the red emission and correlated color temperature (CCT) of these samples are calculated using the CIE (Commission Internationale de l’Eclairage) chromaticity diagram. Our investigation reveals that the present glasses may be utilized as red luminescent materials and red laser source for 5D0 → 7F2 emission at 611 nm.

A novel quinoline derivative containing a phenanthroimidazole moiety: Synthesis, physical properties and light-emitting diodes application

The deep-blue emitting material 2-(8-(benzyloxy)quinolin-2-yl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (QL-PPI) which contains 8-(Benzyloxy)quinoline core and phenanthroimidazole moiety, has been designed and synthesized. The non-doped OLED using QL-PPI as the emitting layer shows emission at 455 nm, full width at half maximum of 100 nm, maximum brightness of 250 cd m−2, maximum current efficiency of 0.47 cd A−1, and Commission Internationale de L'Eclairage (CIE) coordinate of (0.20, 0.22). Furthermore, the QL-PPI with a slight mass concentration in the silica gel is coated on the near ultraviolet (NUV) chip (380 nm) to prepare the hybrid deep-blue LED device HB1 with a y coordinate = 0.0541. The hybrid WLED device HW1 based on QL-PPI mixed with green phosphor [(Ba, Sr)2SiO4: Eu2+] and red phosphor [(Sr, Ca)2AlSiN3: Eu2+] is prepared. The hybrid WLED exhibits luminance efficiency of 18.05 lm W−1 (at 19.90 mA), Correlated Color Temperature (CCT) of 4580 K, Color Rendering Index (CRI) of 80, and CIE chromaticity coordinate of (0.3571, 0.3562). These results reveal that the QL-PPI can apply both in OLED and the hybrid LED simultaneously. The QL-PPI which used in the hybrid WLED has the potential to reduce reliance on rare-earth metals and improve the CRI of the hybrid WLED.

Enhanced local symmetry achieved zero-thermal-quenching luminescence characteristic in the Ca2InSbO6:Sm3+ phosphors for w-LEDs

A material’s structure vitally affects its luminescence property, which in turn determines its application. Therefore, understanding the correspondence between structural local symmetry and luminescence characteristics is vital for the design and synthesis of optical materials. A series of solid solution reddish-orange-emitting phosphors Ca2InSbO6:Sm3+ (CISO:Sm3+) was synthesized by the high-temperature solid-phase method and applied for white-light-emitting diodes (w-LEDs). Under 407 nm excitation, CISO:Sm3+ phosphors showed intense reddish-orange emission at 600 nm that is attributed to the 4G5/2 → 6H7/2 transition of Sm3+ ions. Given that Sm3+ ions are a structural probe, the relationship between their local symmetry and luminescence properties was discussed in detail. The photoluminescence intensity of CISO:Sm3+ phosphors continuously increases with rising temperature from 298 to 480 K based on the enhanced local symmetry. This phenomenon was further analyzed using the trap theory and charge compensation mechanism. High color purity (~99.9%) and proper Commission International del′Eclairage (CIE) chromaticity coordinates were achieved for the CISO:Sm3+ phosphors. Finally, the fabricated w-LED displayed superior color rendering index (Ra = 93) and CIE chromaticity coordinates (0.330, 0.357) and thus has great potential as reddish-orange-emitting substitutes in horticultural and solid lighting. This work initiates a new insight to construct thermally stable phosphors for optical applications.

Blue Laser Diode-Based Remote Solid-State Lighting Using Plastic Optical Fiber and Phosphor Film for a Hazardous Environment

In this study, we proposed and experimentally demonstrated the blue laser diode-based remote solid-state lighting using plastic optical fiber and phosphor film. The light-emitting part’s vicinity is free of electricity, which eliminates the risk of explosion and electromagnetic interference (EMI) and thus can find wide applications in hazardous or sensitive locations, such as gas plants and aircraft, to name a few. The color attributes of generated white light were studied by calculating correlated color temperature (CCT), color rendering index (CRI), Commission Internationale de l’Eclairage (CIE), and The maximum CRI of 77.6 with a corresponding CCT of 4674 K has been achieved at 360 mA. By changing the bias current from 280 mA to 360 mA, the of the generated light source is extremely small ranging from to which indicates that the obtained white light is perceived as neutral in appearance. The CIE chromaticity coordinates (x, y) of generated white light are very close to the Planckian locus. At 360 mA, CIE chromaticity coordinates (x, y) exhibit at (0.3528, 0.3443), which are very close to the standard neutral white light’s (0.333, 0.333). The proposed technique can be implemented in a hazardous environment.

Multiple Hydrogen Bond-Induced Structural Distortion for Broadband White-Light Emission in Two-Dimensional Perovskites

Low-dimensional hybrid lead-halide perovskites with broadband white-light emission upon near-UV excitation have attracted immense scientific interest due to their potential application for the next...

A novel efficient Mn4+-activated Ba2YTaO6 far-red emitting phosphor for plant cultivation LEDs: Preparation and photoluminescence properties

Novel efficient Ba2YTaO6:Mn4+ (BYT:Mn4+) far-red emitting double-perovskite phosphors for plant cultivation LEDs were reported in this article. These phosphors were successfully synthesized via a traditional high-temperature solid-state reaction method, and their crystal structure, luminescence properties, fluorescence decay lifetimes, Commission Internationale de l'Eclairage (CIE) chromaticity coordinates, internal quantum efficiency, and thermal stability have been systematically investigated. XRD Rietveld refinement demonstrated that the BYT:Mn4+ compound crystallized into cubic crystal system with Fm3‾m space group, and the lattice parameter were a = b = c = 8.445 (7) Å, α = β = γ = 90°, and V = 602.231 (10) Å3. Interestingly, the obtained samples showed an intense far-red emission band centered at 690 nm under excitation of 360 nm, which matched well with the absorption band of phytochrome PFR. In BYT:Mn4+ phosphors, the Mn4+ ions occupied the TaO6 octahedron by replacing the Ta5+ site, and the optimal doping concentration of Mn4+ ions was determined to be 0.4 mol%. The CIE chromaticity coordinates and internal quantum efficiency of BYT:0.4%Mn4+ phosphors were (0.7283, 0.2717) and 41.5%, respectively. In addition, when the temperature reached at 423 K, the emission intensity of BYT:0.4%Mn4+ phosphors remained 37% of that at 303 K. Therefore, all of these investigations demonstrated that BYT:Mn4+ phosphors could be used as potential far-red emitting phosphors for plants cultivation LEDs.

Spectral properties and Judd–Ofelt analysis of novel red phosphors Gd2InSbO7:Eu3+ with high color purity for white LEDs

Gd2InSbO7:Eu3+ red phosphors were successfully synthesized via high-temperature solid–state reaction. The phase purity, particle size, and luminescence properties of obtained phosphors were measured and analyzed in detail. The Gd2InSbO7 lattice possesses cubic structure with Fd-3m (227) space group. The phosphors emit bright red emission at 628 nm under 393 nm excitation, and this phenomenon is attributed to the 5D0–7F2 transition. The Judd–Ofelt parameters (Ω2, Ω4), transition ratio, and branching ratios (β) of Eu3+-doped Gd2InSbO7 phosphor were calculated on the basis of the emission spectra and decay lifetimes. The optimal content in Gd2InSbO7:xEu3+ is identified to be 15 mol%. The thermal quenching of Gd2InSbO7:Eu3+ is found to be over 500 K, and its activation energy is 0.26 eV. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of Gd2InSbO7:15%Eu3+ are (0.629, 0.371), which are close to ideal red chromaticity coordinates (0.670, 0.330). The fabricated w-LED exhibits good color rendering index (Ra) (86), correlated color temperature (CCT) (6997 K), and CIE chromaticity coordinates (0.302, 0.330). The obtained results demonstrate that Gd2InSbO7:Eu3+ phosphors have potential applications in white LEDs.

Abnormal thermal quenching and application for w-LEDs: Double perovskite Ca2InSbO6:Eu3+ red-emitting phosphor

Double perovskite compounds have the advantages of excellent chemical stability. Herein, a series of red-emitting Ca2InSbO6 (CISO):Eu3+ phosphors were synthesized through the high-temperature solid-state method. Phase purity, elemental composition, photoluminescence properties, and luminescence decay were investigated in detail. Under 395 nm excitation, the CISO:0.80Eu3+ phosphor manifested a brilliant red emission peak at 616 nm due to the 5D0→7F2 transition of Eu3+. The optimal doped concentration of Eu3+ was 0.80 mol. The critical distance (Rc = 8.41 Å) was calculated. The dominant concentration-quenching mechanism of Eu3+ was ascribed to the electric dipole–dipole interaction. Compared with commercial red phosphors (e.g., Y2O2S:Eu3+, and Y2O3:Eu3+), the Commission International del’Eclairage (CIE) chromaticity coordinates of the CISO:0.80Eu3+ phosphor (0.656, 0.338) were very close to those of the National Television System Committee [(0.670, 0.330)]. Impressively, the CISO:Eu3+ phosphors exhibited abnormal thermal-quenching phenomenon. Up to 380 K, the CISO:0.80Eu3+ phosphor did not exhibit thermal quenching, and its intensity increase was about 14%. The thermal-quenching mechanism was studied in detail, and the thermal activation energy (Ea) was found to be 0.34 eV. The CISO:0.80Eu3+ phosphor also had a high color purity (98.2%). Moreover, the internal quantum efficiency of the CISO:0.80Eu3+ phosphor reached as high as 82%. Thus, a white light-emitting diode (w-LED) with low CCT (4553 K), Ra (88.1), and CIE chromaticity coordinates of (0.345, 0.361) were obtained. All these results demonstrated the potential of the Ca2InSbO6:Eu3+ phosphors as red-emitting substitutes for w-LEDs.

KCa2Mg2V3O12: A novel efficient rare-earth-free self-activated yellow-emitting phosphor

The development of efficient near-ultraviolet (near-UV) excitable inorganic phosphors is highly important for application in near-UV-pumped white light-emitting diodes (LEDs). Herein, we reported on a novel efficient rare-earth-free yellow-emitting KCa2Mg2V3O12 vanadate phosphor. These phosphors were prepared by using a conventional high-temperature solid-state reaction method. Photoluminescence study revealed that KCa2Mg2V3O12 phosphor exhibited a broad excitation band in the 250−420 nm wavelength range with a peak at 346 nm, owing to the absorption of [VO4]3− groups. Upon 346 nm excitation, KCa2Mg2V3O12 phosphor showed bright yellow emission in the 400−800 nm range with a maximum at 540 nm and a full width at half maximum of 161 nm. Such self-activated broadband yellow luminescence was attributed to the 3T2→1A1 and 3T1→1A1 transitions of [VO4]3− groups. The Commission Internationale de l´Eclairage (CIE) color coordinates were calculated to be (0.3741, 0.4679), which were located in the yellow region in the CIE chromaticity diagram. Impressively, the internal quantum efficiency of KCa2Mg2V3O12 phosphor was measured to be as great as 41 %. In addition, the temperature-dependent emission spectra were recorded, and the activation energy Ea was determined to be 0.366 eV. The newly developed KCa2Mg2V3O12 phosphor might have application potential as color converter in white LEDs.

Applying InP/ZnS Green-Emitting Quantum Dots and InP/ZnSe/ZnS Red-Emitting Quantum Dots to Prepare WLED With Enhanced Photoluminescence Performances

Based on blue LED chips to excite Ce-doped yttrium aluminum garnet (YAG: Ce3+) yellow phosphors, InP/ZnS green-emitting quantum dots (QDs) and InP/ZnSe/ZnS red-emitting QDs are used as light conversion materials for WLEDs to improve the color rendering index (CRI) of the device and improve its color coordinates. We have proven this in previous work. But in the previous work, we only studied the CRI of the driving current from 5 mA to 100 mA. The CRI and the Commission International de L’Eclairage (CIE) chromaticity coordinates of the WLED device prepared before is not ideal under high current conditions. The emission peak position of InP/ZnSe/ZnS red-emitting QDs we used in previous work is 605nm. In this article, we adjusted the emission peak position of InP/ZnSe/ZnS red-emitting QDs to 611nm, and prepared WLED in the same way, which improved the problem that the CRI of WLED devices decreases rapidly and the chromaticity coordinates change greatly under high current conditions. The CRI of prepared WLED device in this article was increased to 91.0, the CIE chromaticity coordinates is (0.3365, 0.3334), and the correlated color temperature (CCT) is 5313 K. We also tested the dependence of the electroluminescence (EL) spectrum, CRI, CCT and chromaticity coordinates of the prepared WLED device on the current. Compared with the prepared WLED device before, the CRI of the WLED device prepared in this article has always remained above 90, hovering between 90 ~ 91, very stable. The chromaticity coordinate distribution is also very concentrated, the amplitude of the offset black body radiation is small, and it shows excellent color rendering and stable working performance. A 30-day aging test was performed on the prepared WLED device.

Synthesis and optical temperature sensing performance of NaLa(MoO4)2: Tb3+, Eu3+ phosphors

Abstract NaLa(MoO 4 ) 2 : Tb 3+ , Eu 3+ phosphors were prepared via the hydrothermal method using sodium citrate as chelating agent, and different morphologies of the samples were obtained through the change of the Na 3 Cit molar ratio to rare earth ions. The NaLa(MoO 4 ) 2 : Tb 3+ , Eu 3+ phosphors' structure, morphology, and temperature sensing performance were investigated using XRD (X-ray diffraction) and FE-SEM (Field Emission Scanning Electron Microscope) as well as temperature-dependent emission spectra. The XRD demonstrated that all the materials are body-centered tetragonal phase. The FE-SEM results show that a dosage of sodium citrate could control the NaLa(MoO 4 ) 2 : Tb 3+ , Eu 3+ phosphors' morphology. On the basis of the temperature-dependent emission spectra, the FIR (Fluorescence Intensity Ratio) of Eu 3+ and Tb 3+ in all the samples changed with the temperature and could represent the temperature. Furthermore, the phosphors' sensitivity increased with the value of Cit 3− /Re 3+ . Simultaneously, observed from the CIE (Commission International del’Eclairage) chromaticity coordinates, the range of the samples' luminescence color variation expanded with the Cit 3− /Re 3+ increases.

Color-tunable visible photoluminescence of Eu:CaF2 single crystals: variations of valence state and local lattice environment of Eu ions

In this article, Eu-activated CaF2 single crystals were synthesized by Bridgman-Stockbarge method. The dependence of photoluminescence properties of Eu: CaF2 crystals in UV-Vis regions on EuF3 doping concentrations were investigated. While the EuF3 doping concentration is increased from 0.6% to 6.0%, the CIE (Commission Internationale de L'Eclairage) color coordinates of Eu: CaF2 crystals can be tuned from (0.28, 0.12) to (0.60, 0.38), corresponding to the luminescence color from blue to orange. XPS (X-ray Photoelectron Spectroscopy) measurements indicated that Eu2+ and Eu3+ ions both existed in the crystals. With EuF3 doping concentration increasing, the proportion of Eu3+ ions increase from 16.73% to 39.00%, while that of Eu2+ ions decrease from 83.27% to 61.00%. Moreover, the integrated intensity ratio (R) of the 614 nm to 593 nm of Eu3+ ions increase from 0.38 to 0.44, indicating the local lattice environment symmetry of Eu3+ ions become lower with higher EuF3 doping concentrations. Furthermore, the CIE chromaticity coordinates of Eu: CaF2 crystals greatly depend on the excitation wavelength. The warm white-light emission has been realized in 0.6%Eu: CaF2 crystal when the excitation wavelength is around 322 nm.

Layered Structure Produced Nonconcentration Quenching in a Novel Eu3+-Doped Phosphor

Energy migration (energy transfer among identical luminescence centers) is always thought to be related to the concentration quenching in luminescence materials. However, the novel Eu3+-doped Ba6Gd2Ti4O17 phosphor seems to be an exception. In the series of Ba6Gd2(1- x)Ti4O17: xEu3+ ( x = 0.1, 0.3, 0.5, 0.7, and 0.9) phosphors prepared and investigated, no concentration quenching is found. Detailed investigations of the crystal structure and the luminescence properties of Ba6Gd2(1- x)Ti4O17: xEu3+ reveal that the nonoccurrence of concentration quenching is related to the dimensional restriction of energy migration inside the crystal lattices. In Ba6Gd2Ti4O17, directly increasing the number of Eu3+ ions to absorb as much excitation energy as possible allows to achieve a higher brightness. The highly Eu3+-doped Ba6Gd2(1- x)Ti4O17: xEu3+ ( x = 0.9) sample can convert near-UV excitation into red light, whose Commission Internationale de l'Eclairage (CIE) coordinates are (0.64, 0.36) and the color purity can reach up to 94.4%. Moreover, warm white light with the CIE chromaticity coordinates of (0.39, 0.39), the correlated color temperature of 3756 K, and the color rendering index of 82.2 is successfully generated by fabricating this highly Eu3+-doped phosphor in a near-UV light-emitting diode chip together with the green YGAB:Tb3+ and blue BAM:Eu2+ phosphors.