Narrow-Band Red-Emitting Phosphors with High Color Purity, Trifling Thermal and Concentration Quenching for Hybrid White LEDs and Li3Y3BaSr(MoO4)8:Sm3+, Eu3+-Based Deep-Red LEDs for Plant Growth Applications.

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.

Narrow-band red-emitting phosphor with negligible concentration quenching for hybrid white LEDs and plant growth applications.

Narrow-band red-emitters are the key to solving problems encountered by the current white LED technology. In this context, a series of new red-emitting Li3BaSrLa3(MoO4)8:Eu3+ phosphors were synthesized and characterized through various spectroscopic methods. All phosphor compositions were crystallized in the monoclinic phase, with space group C2/c. A broad charge transfer (O2-→ Mo6+) extended up to the blue region along with strong 7F0→5L6, 5D3 absorption, making them looked-for materials for warm white LED applications. The concentration quenching study reveals that there was no concentration-quenching occuring and the quantum yield of this non-concentration-quenching Li3BaSrLa0.3Eu2.7(MoO4)8 phosphor reaches 92.6%. The Li3BaSrLa0.3Eu2.7(MoO4)8 retain >80% of its emission intensity at 150 °C. The best red-emitting composition was integrated with near UV LED and obtained bright red emission with CIE x = 0.6647, y = 0.3357. White LED was fabricated by integrating the blue LED with yellow dye + red phosphor and white LED showed bright white light with CCT (5546 K), CIE (0.331, 0.385), and CRI (81%). In addition, the red LED spectrum is well-matched with the phytochrome (Pr) absorption spectrum and is useful for plant growth applications.

Narrow band red emitting europium complexes and their application in smart white LEDs and vapoluminescent sensors.

Narrow band red emitting phosphors play a vital role in high performance smart white LEDs. In this context, a series of new Eu(iii) complexes have been synthesized with neutral ligands (C1-functionalised phenanthro-imidazole-based ancillary ligands substituted with phenyl moieties (m-CF3, p-CF3, p-CH3 and 1-naphthyl and 2-naphthyl group)) and dibenzoylmethane (DBM) as an anionic ligand. All the newly synthesized Eu-complexes showed extremely narrow band red emission due to the electric dipole transition (5D0-7F2, both in solid and thin film) with high quantum efficiency. A combined experimental and theoretical study indicates that the energy transfer from the ligand to the metal ion is complete. A temperature dependent photoluminescence (PL) study in solution reveals that the red emission is retained (only the ED (5D0-7F2) intensity decreases with increasing temperature). Red LEDs and hybrid white LEDs were fabricated by using a near UV LED chip with europium complexes and a near UV/blue LED conjugated with a yellow organic dye and europium complex mixture, respectively. Hybrid white LEDs (Eu(DBM)3Phen-pCN-pCF3 + yellow organic dye) showed superior CRI (84%) and CIE (x = 0.36, y = 0.39) values (near UV based) and CRI (82%) and CIE (x = 0.34, y = 0.36) values (blue LED based). In addition, the studied Eu-complexes herein showed excellent reversible on-off-on luminescence behavior with exposure to acid-base vapours. Detailed spectroscopic investigation reveals that the protonation of the Eu-complexes (ligands) plays a key role in the on-off-on luminescence.