Trivalent europium-based monochromatic
red light-emitting phosphors
are an essential component to realize high-performance smart lighting
devices; however, the concentration and thermal quenching restrict
their usage. Here, we report a series of efficient Eu3+-substituted Li3Y3BaSr(MoO4)8 red-emitting phosphors based on a stratified scheelite structure
with negligible concentration and thermal quenching. All of the host
and phosphor compositions crystallize in monoclinic crystal structure
(space group C2/c). All of the phosphor
compositions produce narrow-band red emission (FWHM ∼6 nm),
which is highly apparent to the human eyes, and lead to exceptional
chromatic saturation of the red spectral window. Concurrently, detailed
investigations were carried out to comprehend the concentration and
thermal quenching mechanism. Absolute quantum yields as high as 88.5%
were obtained for Li3Y0.3Eu2.7BaSr(MoO4)8 phosphor with virtuous thermal stability (at
400 K, retaining 87% of its emission intensity). The light-emitting
diodes were constructed by coupling Li3BaSrY0.3Eu2.7(MoO4)8 red phosphor with a
near-UV LED chip (395 nm) operated at 20 mA forward bias, and the
hybrid white LED (an organic yellow dye + red Li3Y3BaSr(MoO4)8:Eu3+ phosphor
integrated with an NUV LED chip) showed a low CCT (6645 K), high CRI
(83) values, and CIE values of x = 0.303; y = 0.368, which indicated that the synthesized phosphors
can be a suitable red component for white LEDs. In addition, we have
systematically investigated the Sm3+ and Sm3+, Eu3+ activation in Li3Y3BaSr(MoO4)8 to display the latent use of the system in plant
growth applications and establish that the phosphor exhibits orange
red emission with an intense deep-red emission (645 nm (4G5/2 → 6H9/2)). The phytochrome
(Pr) absorption spectrum well matched the fabricated deep-red LED
(by integrating a NUV LED + Li3Y3BaSr(MoO4)8:Sm3+ and Eu3+ phosphor)
spectral lines.
Red emitting Li3BaSrGd3 -x Eu x (MO 4 ) 8 (M = W, Mo) phosphors with stratified scheelite structure have been synthesized by conventional solid state reaction. All the compositions crystallize in the monoclinic structure with space group C2/c. Host as well as the phosphors (Eu 3 + substituted) show broad absorption band in the UV to near UV region, due to the oxygen to molybdenum (absorption edge~360 nm, O 2À ! Mo 6 + ) or tungsten (absorption edge~320 nm, O 2À ! W 6 + ) charge transfer transition. The photoluminescence(PL) study of Eu 3 + substituted compositions show emission at~615 nm (due to the forced electric dipole (ED) 5 D 0 ! 7 F 2 transition of Eu 3 + ion), which confirms that the Eu 3 + ion present in the non-centrosymmetric site. In order to study the emission behaviour systematically the Judd-Ofelt (J -O) spectral intensity parameters were calculated. The Commission Internationale de l'Elcairage (CIE) colour coordinate values are well harmonized with the National Television Standard Committee (NTSC) standards. The presently synthesized tungstate phosphors have been used as reference for contrast between two. The entire compositions show better absorption in the near UV to blue region and emitting red light~615 nm indicates that this phosphor may find potential application as a red phosphor for white LED.
Three ancillary ligands based on imidazo-bipyridyl with phenyl (Ph), naphthyl (Np), and triphenylamine (TPA) substitution were synthesized and secondhand to formulate the consistent europium(III) ternary complexes using thenoyltrifluoroacetone as an anionic ligand. The complete investigation of spectroscopic, photophysical, and electrochemical properties was carried out. The attained results for all the ancillary ligands and their corresponding Eu complexes were compared with one another. All the Eu complexes reveal a broad excitation band ranging from the near-UV to blue region, along with high intense emission and apposite color purity. To further understand the ligand-to-metal energy transfer (ET) process, the geometry of the ligand was optimized and the energy level location (singlet and triplet) was calculated by using DFT and TD-DFT calculations. On the basis of the theoretical calculation, the ET mechanism was proposed. From PL emission spectra in the solid state, complete ET occurs from Ph, Np based ancillary ligands to the Eu ion, which yields a pure red emission, whereas the TPA functionalized based Eu complex shows incomplete ET. Fortunately, white emission was observed in the TPA based Eu complex in the solid state. The white LED was fabricated by using a white emitting complex integrated with 395 nm emitted LED (InGaN) chips under 20 mA forward-bias current. The excitation source from LED was fully observed by the complex shown for 3Eu and showed yellowish emission in different concentrations (the similar observation also reflected in solid). However, in the case of 1Eu and 2Eu complexes, they showed close to white emission. The Commission International de I'Eclairage (CIE) chromaticity coordinates are close to the National Television Standard Committee standard value for white emission, and in addition, the complex 3Eu coated with the blue LED chip (460 nm) by PMMA (1:10) showed bright white emission with CIE x, y values of 0.30, 0.33, respectively.
Dual emissive single-component white light emissive luminogens are promising color convertors for white light emitting diodes. In this context, a new class of bipolar phenanthroimidazole based (N1 functionalization with Ph,...
A new diphenylamine-functionalized ancillary-ligand-coordinated europium(III) β-diketonate complex showed incomplete photoexcitation energy transfer from a ligand to a Eu ion. A solvatochromism study led to a balancing of the primary colors to obtain single-molecule white-light emission. Thermal-sensing analysis of the europium complex was executed. The europium complex, conjugated with a near-UV-light-emitting diode (395 nm), showed appropriate white-light-emission CIE color coordinates (x = 0.34 and y = 0.33) with a 5152 K correlated color temperature.
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