Synthesis and Optical Properties of New Red Emitting Phosphor Li3 BaSrGd3-x Eux (MO4 )8 for White LEDs

Narrow-band dazzling red-emitting (LiCaLa(MoO4)3:Eu3+) phosphor with scheelite structure for hybrid white LEDs and LiCaLa(MoO4)3:Sm3+,Eu3+-based deep-red LEDs for plant growth applications

Presently, the preparation of dazzling narrow-band red-emitting phosphors for solid-state lighting is still a challenge. In this context, herein, a series of pure narrow-band red-emitting LiCaLa1-xEux(MoO4)3 phosphors was synthesized and characterized, and their spectroscopic properties were systematically studied. In addition, a series of orange-red-emitting LiCaLa1-ySmy(MoO4)3 phosphors with the simultaneous doping of Eu3+ was synthesized for plant growth applications. The optical studies revealed that the phosphors showed pure red emission with a full width at half maximum of ∼5 nm and 97% color purity. Alternatively, their absorption spectrum showed good absorption strength in the near UV to blue region. Non-concentration quenching behavior was observed even when the concentration of Eu3+ in the lattice was 100%. The dominant electric dipole transition in the emission spectrum indicated that the Eu3+ ion occupies a non-centrosymmetric site in the lattice. At 150 °C, the phosphor retained 88.83% of its emission intensity calculated at room temperature. Thus, it can be useful for the fabrication of LEDs. Subsequently, Eu-rich red and white LEDs (integrated with yellow phosphor) were fabricated with near-UV and blue LED chips, respectively. The fabricated hybrid white LED showed pure white emission with a CCT of 4762 K, CRI of 81%, and close CIE coordinates of (0.34, 0.33). The absolute quantum yield for the fully substituted LiCaEu(MoO4)3 composition was calculated to be 44.50% upon excitation at 395 nm. To utilize LED light for plant growth applications, efforts were made to synthesize orange-red (Sm3+) and deep-red (Sm3+, Eu3+) phosphors and utilize the simultaneously doped phosphor for the fabrication of deep-red LEDs. The spectral lines well-matched the spectrum of phytochrome (Pr). Thus, the phosphor in the present study is a potential candidate as a red and deep-red phosphor for the fabrication of hybrid white LEDs and deep-red LEDs (for plant growth purposes), respectively.

Recent progress in trivalent europium (Eu3+)-based inorganic phosphors for solid-state lighting: an overview

Narrow band red-emitting phosphors are significant constituents but still a bottleneck for next-generation smart displays and high-performance lighting (solid-state lighting based white light-emitting diodes (WLEDs)) technology. This review emphasizes the fundamental understanding and comprehensive overview of the recent progress and challenges associated with inorganic phosphors or down (wavelength) convertors, providing special attention to narrowband red-emitting oxide phosphors for phosphor-converted WLEDs (pc-WLEDs). In this context, the comprehensive progress on trivalent europium (Eu3+, in scheelite and double perovskite structures) based oxide phosphors with special emphasis on structure-composition-property-correlations is briefly reviewed. Furthermore, the challenges faced in the design of new oxide red phosphors and strategies to improve their absorption, emission efficiency, and future research direction are highlighted.

Stable and efficient narrow-band red emitters with high colour purity for white LEDs and plant growth applications

The search for extremely narrow-band new red emitters is essential for smart displays and lighting applications. Herein, we report the synthesis of a series of red-emitting Eu³⁺-substituted Li₃BaSrY₃(WO₄)₈ and solid-solution (Li₃BaSrY_0.3Eu_2.7(WO₄)_8-y(MoO₄)_y) phosphors with a stratified scheelite structure and the systematic investigation of their optical properties. All the compositions show broad absorption (charge transfer (O^2- → M⁶⁺)) extended up to the blue region along with strong characteristic Eu³⁺ excitation lines. The phosphor compositions exhibit proficient narrow-band red emission (quantum yield up to 85%; full width at half maximum (FWHM) = 6 nm; CIE colour coordinates x = 0.65, y = 0.35, i.e. approaching the NTSC standard for red colour) of exceptional colour purity (94% to 98%), and this host supports heavy trivalent Eu activation (showing zero concentration quenching of the emission (Eu-rich lattice)). The dominating electric dipole (⁵D₀ → ⁷F₂, red emission) transition shows Eu³⁺-ion occupancy in the non-centrosymmetric site in the host lattice. The selected composition shows better absolute quantum efficiencies compared to commercial phosphors. The presently synthesized phosphors have proven to be thermally stable against the temperature quenching effect. The fabricated red LED showed excellent performance, colour purity, LER and CIE values. The excellent optical properties, quantum yield and thermal stability make the phosphor applicable as a red component in solid-state lighting devices and as a light source for plant growth applications.

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 Li₃Y_0.3Eu_2.7BaSr(MoO₄)₈ phosphor with virtuous thermal stability (at 400 K, retaining 87% of its emission intensity). The light-emitting diodes were constructed by coupling Li₃BaSrY_0.3Eu_2.7(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 (⁴G_5/2 → ⁶H_9/2)). 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.

Layer-structure-suppressed concentration quenching of Dy3+ luminescence and the realization of a single phase white light-emitting phosphor cooperated with Tm3+

A special layered structure helps to suppress the concentration quenching to achieve high dysprosium–thulium co-doping single-phase white light.

A study of negative-thermal-quenching (Ba/Ca)AlSi5O2N7:Eu2+ phosphors

Phosphor is an important part of the new generation of light-emitting diodes (LEDs), which requires high luminous intensity and high-temperature resistance. In this study, a series of excellent (Ba_1-x-yCa_x)AlSi₅O₂N₇:yEu²⁺ phosphors was developed, which were synthesized by a high-temperature solid-state reaction in a reducing atmosphere. In addition, the crystallinity and luminescence intensity of the samples could be enhanced by some amount of Ca²⁺ substitution. The luminescence intensity was the highest when the Eu²⁺ concentration reached 0.06. Furthermore, the thermal stability of the luminescence was studied in detail. The results were satisfactory, showing that the luminescence intensity of the (Ba_1-xCa_x)AlSi₅O₂N₇:Eu²⁺ phosphors exhibited unique negative-thermal-quenching characteristics both at high (273-473 K) and low (4-273 K) temperatures. And the phosphor combined with UV LED chip and red phosphor Sr₂Si₅N₈:Eu²⁺ can achieve a CRI of 90.4 in white LED application which indicated the (Ba_1-xCa_x)AlSi₅O₂N₇:Eu²⁺ phosphor has potential in LED applications.

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 (O^2-→ 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 Li₃BaSrLa_0.3Eu_2.7(MoO₄)₈ phosphor reaches 92.6%. The Li₃BaSrLa_0.3Eu_2.7(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.

Zero-concentration quenching: a novel Eu3+ based red phosphor with non-layered crystal structure for white LEDs and NaSrY(MoO4)3:Sm3+ based deep-red LEDs for plant growth

Oxide based highly efficient narrow band red emitting phosphors are still a bottleneck in white LED applications. Trivalent europium ion based phosphors could be a better choice, however their weak oscillator strength restricts their use in white light emitting diodes (LEDs). Herein, we report a novel red emitting NaSrEu(MoO₄)₃ (NSEuM) phosphor with zero concentration quenching (non-layered crystal structure). The phosphors (NaSrY_1-xEu_x(MoO₄)₃, x = 0.1-1, in increments of 0.1) were synthesized through a traditional solid-state reaction and their phase formations were analyzed by powder X-ray diffraction (PXRD) followed by Rietveld refinement. Under 395 nm excitation, all the phosphors showed sharp emission at 616 nm (full width at half maximum, FWHM ∼4-5 nm) owing to the ⁵D₀→⁷F₂ electric dipole transition of the Eu³⁺ ion. A concentration dependent photoluminescence (PL) study revealed that there is no concentration quenching of the systems, leading to them having superior emission characteristics over those of commercial red phosphors as well as a reported Eu³⁺ phosphor with a layered structure. The color purity of the synthesized phosphor was observed to be 96.32% and it shows excellent thermal stability at 423 K, retaining 64.6% of the emission intensity of its initial room temperature. The NSEuM phosphor shows a high absolute quantum yield of 79.7%. Besides this, a red LED (near UV (NUV) LED chip with the NaSrEu(MoO₄)₃ phosphor) as well as a hybrid white LED (NUV LED chip with an organic yellow dye + red NSEuM phosphor) were fabricated and their optical properties were studied. After the inclusion of the red phosphor in the hybrid white LED, the color rendering index (CRI)/correlated color temperature (CCT) were improved significantly (60/9333 K vs. 79/6004 K, respectively). In addition, to show the potential use of the system in plant growth application, we systematically investigated the Sm³⁺ activation in NaSrY(MoO₄)₃ and found that the phosphor shows orange red emission with an intense deep red emission (645 nm (⁴G_5/2→⁶H_9/2)). We fabricated a hybrid red/deep red LED by integrating a NUV LED with a mixed Sm³⁺ and Eu³⁺ phosphor and the spectral lines were well matched with the phytochrome (Pr) absorption spectrum. The presently investigated phosphor showed potential in a white LED as well as a deep red/orange-red LED for plant growth.

High performance red/deep-red emitting phosphors for white LEDs

NaSrGd(MoO₄)₃:Eu³⁺ red phosphor exhibits higher quantum efficiency (82%) and the fabricated white LED showed 74% CRI and 6823 K CCT.

Systematic investigation of Eu3+ activated Na2Ln4(MoO4)7 [Ln = La, Gd and Y] narrow band red emitting phosphors for hybrid white LEDs and plant growth

A sequence of Eu³⁺ activated Na₂Ln₄(MoO₄)₇ [Ln = La, Gd and Y] red phosphors has been synthesized using a conventional solid-state method.

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

The synthesized molecular Eu-complex based hybrid white LED showed superior color rendering index. In addition, the complex also showed on-off-on luminescence with exposure to acid–base vapours.

Neutralizing the Charge Imbalance Problem in Eu3+-Activated BaAl2O4 Nanophosphors: Theoretical Insights and Experimental Validation Considering K+ Codoping

In recent years, rare-earth-doped nanophosphors have attracted great attention in the field of luminescent materials for advanced solid-state lighting and high-resolution display applications. However, the low efficiency of concurrent red phosphors creates a major bottleneck for easy commercialization of these devices. In this work, intense red-light-emitting K⁺-codoped BaAl₂O₄:Eu³⁺ nanophosphors having an average crystallite size of 54 nm were synthesized via a modified sol-gel method. The derived nanophosphors exhibit strong red emission produced by the ⁵D₀ → ⁷F _J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ upon UV and low-voltage electron beam excitation. Comparative photoluminescence (PL) analysis is executed for Eu³⁺-activated and K⁺-coactivated BaAl₂O₄:Eu³⁺ nanophosphors, demonstrating remarkable enhancement in PL intensity as well as thermal stability due to K⁺ codoping. The origin of this PL enhancement is also analyzed from first-principles calculations using density functional theory. Achievement of charge compensation with the addition of a K⁺ coactivator plays an important role in increasing the radiative lifetime and color purity of the codoped nanophosphors. Obtained results substantially approve the promising prospects of this nanophosphor in the promptly growing field of solid-state lighting and field emission display devices.

Photoluminescence properties of novel Ba2Lu5B5O17:Eu3+ red emitting phosphors with high color purity for near-UV excited white light emitting diodes

A series of new red-emitting Ba₂Lu_4.98−xEu_xLa_0.02B₅O₁₇ (0.1 ≤ x ≤ 1.0) phosphors were synthesized via the high-temperature solid-state reaction method. The phase formation of the as-synthesized Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ phosphor was confirmed by powder X-ray diffraction analysis. It was found that La³⁺ doping resulted in the reduction of LuBO₃ impurities and thus pure phase Ba₂Lu₅B₅O₁₇ was realised. The morphology of Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ phosphors was studied by field emission scanning electron microscopy (FE-SEM). As a function of Eu³⁺ concentration the photoluminescence spectra and decay lifetimes were investigated in detail. Under excitation at 396 nm, a dominant red emission peak located at 616 nm (⁵D₀ → ⁷F₂) indicated that Eu³⁺ ions mainly occupied low symmetry sites with a non-inversion center in Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇. The optimal Eu³⁺ ion concentration was found to be x = 0.5 and the critical distance of Eu³⁺ was determined to be 6.55 Å. In addition, the concentration quenching takes place via dipole–dipole interactions. The phosphors exhibited good CIE (Commission International de I'Eclairage) color coordinates (x = 0.643, y = 0.356) situated in the red region and a high color purity of 97.8%. Furthermore, the internal quantum efficiency and the thermal stability of Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ phosphors were also investigated systematically. The results suggest that Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ may be a potential red phosphor for white light-emitting diodes.

Novel Ba₂Lu₅B₅O₁₇:Eu³⁺ red emitting phosphors with high color purity were prepared for near-UV excited white light emitting diodes.

Effects of electron-withdrawing groups in imidazole-phenanthroline ligands and their influence on the photophysical properties of EuIII complexes for white light-emitting diodes

The red light emitting diode (LED) was fabricated by using europium complexes with InGaN LED (395 nm) and shown digital images, corresponding CIE color coordinates (red region) as well as obtained highest quantum yield of the thin film (78.7%).