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

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.

Synthesis, Photoluminescent Characteristics and Eu3+-Induced Phase Transitions in Sr3Zr2O7:Eu3+ Red Phosphors

Designing phosphors that are excited by blue light is extraordinarily important for white light-emitting diodes (w-LEDs). In the present study, a new Ruddlesden-Popper type of SZO:xEu³⁺ (x = 0.01~0.10) phosphors was developed using solid-state reactions. Interestingly, a Eu³⁺ doping-induced phase transformation from the Sr₃Zr₂O₇ (cubic) to the SrZrO₃ (orthorhombic) phase was observed, and the impact of the occupied sites of Eu³⁺ ions on the lifetime of Sr₃Zr₂O₇:xEu³⁺ phosphors is discussed in detail. Diffuse reflectance spectroscopy results showed that the band gap of SZO:xEu³⁺ phosphors gradually increased from 3.48 eV for undoped Sr₃Zr₂O₇ hosts to 3.67 eV for SZO:0.10Eu³⁺ samples. The fluorescence excitation spectrum showed that ultraviolet (300 nm), near-ultraviolet (396 nm) and blue light (464 nm) were all effective excitation pump sources of Sr₃Zr₂O₇:xEu³⁺ phosphors, and the strongest emission at 615 nm originated from an electric dipole transition (⁵D₀→⁷F₂). CIE coordinates moved from orange (0.5969, 0.4267) to the reddish-orange region (0.6155, 0.3827), and the color purity also increased. The fabricated w-LED was placed on a 460 nm chip with a mixture of YAG:Ce³⁺ and SZO:0.1Eu³⁺ samples and showed "warm" white light with a color rendering index (CRI) of 81.8 and a correlation color temperature (CCT) of 5386 K, indicating great potential for application in blue chip white LEDs.

Multiple Charge Transfer Bands Induced Broad Excitation Eu3+ Red Emission in a Vanadium Phosphate System for White Light-Emitting Diodes

In order to realize broad excitation and narrow emission red light phosphor, a new vanadium phosphate Ba₂BiV₂PO₁₁ was selected as a host for Eu³⁺. Monitored at 619 nm, a wide band from 240 to 400 nm could be observed and inferred to be composed of Eu³⁺-O^2- and V⁵⁺-O^2- charge transfer bands, which could make it match well with the UV chip and the blue chip along with the characteristic excitation of Eu³⁺ at 465 nm. Under 354 nm excitation, the sample could emit high color purity red light, and the thermal quenching integral intensity showed good thermal stability. The generation of charge transfer bands was investigated in detail combined with the luminescence properties and the structure of the matrix. Moreover, the as-prepared phosphor could improve the white light performance of blue chip-activated YAG:Ce³⁺ and n-UV chip-activated tricolor phosphors. All the results indicated the multiple application potential of Ba₂BiV₂PO₁₁:Eu³⁺ for white light-emitting diodes.

Highly Efficient Broad-Band Green-Emitting Cerium(III)-Activated Garnet Phosphor Allows the Fabrication of Blue-Chip-Based Warm-White LED Device with a Superior Color Rendering Index

High-performance warm-white light-emitting diode (LED) devices are in great demand toward green and comfortable solid-state lighting. Herein, we report a creative green-emission CaY₂HfGa(AlO₄)₃:Ce³⁺ phosphor. CaY₂HfGa(AlO₄)₃:Ce³⁺ compounds with different cerium ion doping contents have been successfully prepared through a conventional high-temperature solid-state method, and their phase and crystal structure have been revealed via the powder X-ray diffraction and Rietveld refinement. Impressively, the CaY₂HfGa(AlO₄)₃:Ce³⁺ phosphors exhibit a broad-band excitation, which well covers the wavelength region from the 300 to 500 nm, corresponding to the commercial blue-emitting LED chip. Upon 450 nm excitation, the optimal CaY₂HfGa(AlO₄)₃:2%Ce³⁺ sample shows an intense broad-band green emission (the corresponding testing spectral range: 460-750 nm) with a strongest peak about 534 nm. In addition, the CaY₂HfGa(AlO₄)₃:2%Ce³⁺ sample possesses a broad full width at half-maximum equal to 120 nm; moreover, its CIE chromaticity coordinate and the internal quantum efficiency are determined to be (0.3541, 0.5427) and 72.8%, respectively. A high-quality warm-white LED has been fabricated through incorporating our CaY₂HfGa(AlO₄)₃:2%Ce³⁺ green phosphors and commercial red phosphors with the 450 nm blue LED chip. When upon the 20 mA bias driving current, the LED device demonstrates a bright warm-white light emission, which possesses a satisfactory color rendering index of 91, a low correlated color temperature of 4080 K, as well as a good luminous efficacy of 85.14 lm W^-1. The creative green-emitting CaY₂HfGa(AlO₄)₃:Ce³⁺ garnet phosphor has a bright application prospect toward high-quality warm-white LED lighting.

Dazzling Red-Emitting Europium(III) Ion-Doped Ca2LaHf2Al3O12 Garnet-Type Phosphor Materials with Potential Application in Solid-State White Lighting

Bright red-emitting phosphors with high color purity and high photoluminescence quantum yield (PLQY) are highly demanded for the fabrication of high-performance warm-white light-emitting diodes (LEDs). Herein, we demonstrated a novel efficient Eu³⁺-activated Ca₂LaHf₂Al₃O₁₂ garnet phosphor with excellent luminescence properties for near-ultraviolet (near-UV) excited warm-white LEDs. The Ca₂LaHf₂Al₃O₁₂:Eu³⁺ phosphors exhibited an intense excitation spectrum in the near-UV region with a maximum around 394 nm, and they produced dazzling red luminescence peaking at 592, 614, 659, and 711 nm due to the ⁵D₀ → ⁷F_J (J = 1-4) transitions of Eu³⁺ ions when the excitation wavelength was set at 394 nm. Luminescent properties have been studied as a function of Eu³⁺ doping concentration, and the highest emission intensity was achieved at 50 mol % Eu³⁺, while the dipole-dipole interaction brought the concentration quenching effect. The Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺ sample exhibited CIE chromaticity coordinates of (0.6419, 0.3575) with a color purity of 92.7%, and its PLQY was measured to be 64%. The thermal stability and activation energy of Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺ phosphors were also discussed and analyzed. Finally, we made a near-UV chip-based white LED device in which the Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺ phosphor was utilized as a red ingredient. A bright warm-white light emission was realized from this LED device under 80 mA driving current, accompanied by a high color rendering index (CRI) of 88.3, a low correlation color temperature of 3853 K, and good CIE chromaticity coordinates of (0.3909, 0.3934). These results revealed that these red-emitting Ca₂LaHf₂Al₃O₁₂:Eu³⁺ phosphors have promising application prospect in near-UV-excited warm-white LEDs with high a CRI.

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.

Modulating Optical and Electrical Properties of Oxygen Vacancy Enriched La2Ce2O7:Sm3+ Pyrochlore: Role of Dopant Local Structure and Concentration

This work projected the important role of defects in achieving efficient luminescence and electrical conduction in pyrochlore materials. Undoped and Sm3+ doped La2Ce2O7 (LCO and LCOS) stabilize in defect fluorite...

Efficient and ultra-thermally stable Eu3+ and Sm3+-activated narrow-band red/deep red-emitting phosphors and their versatile applications

A succession of Eu³⁺-activated Na₂Y₄(WO₄)₇ (NYW) red phosphors were synthesised and their optical properties were studied in detail for white LED, latent fingerprint and plant growth applications. The phosphors crystallised in a tetragonal system with space group I4₁/a. The NYW:Eu³⁺ red phosphors demonstrated a line-like emission at 616 nm owing to electric dipole transition, and a systematic concentration-dependent PL study revealed that concentration quenching occurs at x = 1.8 with a color purity of 96.06%. The thermal stability and internal quantum efficiency of the phosphor were found to be ∼75.54% (at 423 K) and 88%, respectively. Furthermore, solid solution phosphors were synthesized to increase QE, which was found to be 91.27%. Specifically, the hybrid white LED exhibits warm white light with high CRI (80) and low CCT (5730 K) values, and these values are further improved (CRI-81, CCT-4274 K) when the WLED is fabricated using the most efficient solid solution phosphor Na₂Y_2.2Eu_1.8(WO₄)₃(MoO₄)₄. The currently synthesized phosphors can be potential candidates for security applications. The selected phosphor compositions can be used for the detection of latent fingerprints. Besides, a succession of Eu³⁺ and Sm³⁺ co-doped phosphors were synthesized and their photophysical properties were studied systematically. The deep red LED was fabricated using the same and this could be a possible light source for plant growth usage.

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.

Deep-red photoluminescence from enhanced 5D0-7F4 transition in Eu3+ doped Ca2Ga2GeO7 phosphors

In order to explore diverse luminescence properties of Eu³⁺ in inorganic phosphors, a series of novel deep-red-emitting Ca₂Ga₂GeO₇ phosphors were successfully synthesized by solid-state reactions. The phase formation was verified by the X-ray diffraction patterns and Rietveld refinement and there is only one kind of Ca²⁺ site in Ca₂Ga₂GeO₇. The excitation spectrum shows typical excitation peaks of Eu³⁺ and the broad band ranging from 200 nm to 300 nm was composed of the charge transfer band of O^2--Eu³⁺ and Ga³⁺-O^2- transition band. The emission spectrum depicts that the intensity of the peak located at 704 nm (⁵D₀ → ⁷F₄) is higher than that of 618 nm (⁵D₀ → ⁷F₂), which finally leads to the deep-red emission of the phosphor with high color saturation. The coordination dodecahedron of EuO8 distorted from a cubic geometry to the square antiprism is responsible for the unusual emission of Eu³⁺. The research of the concentration quenching behavior, lifetime and luminescence decay curves imply that the energy transfer between Eu³⁺ ions finally leads to the concentration quenching, and the interaction type is d-d interaction. The charge compensation, quantum efficiency and the thermal stability of Ca₂Ga₂GeO₇:Eu³⁺ were also studied.

Development of a cyan blue-emitting Ba3La2(BO3)4:Ce3+,Tb3+ phosphor for use in dental glazing materials: color tunable emission and energy transfer

Herein, we demonstrated the possibility of using Ba₃La₂(BO₃)₄:Ce³⁺,Tb³⁺ phosphors in dental glazing paste.

A novel high efficiency and ultra-stable red emitting europium doped pyrophosphate phosphor for multifunctional applications

The RBPO:Eu3+ phosphor developed by the nonlinear optical material-inspired methodology can serve as a potential candidate in solid state lighting applications, artistic appreciation or some applications under extreme conditions.

Multi-peaked broad-band red phosphor Y3Si6N11:Pr3+ for white LEDs and temperature sensing

The indispensable broad-band red phosphors for LED lighting generally show a long emission tail for wavelengths longer than 650 nm, which consumes excitation energy but contributes little luminance. Here, we report, for the first time, a broad red emission band with a steep falling edge at 652 nm, formed of widely distributed 1D2 → 3H4 emission lines of Pr3+ in Y3Si6N11 due to a large Stark splitting of the 3H4 (930 cm-1) and 1D2 (725 cm-1) levels. The red emission exhibits a 43 nm bandwidth, which is the widest in Pr3+-doped phosphors reported so far. The red Y3Si6N11:Pr3+ phosphor was applied for the fabrication of 310 nm UV chip-based white LEDs, and a high color rendering index of 96 at a low correlated color temperature of 4188 K was achieved. Furthermore, a temperature-sensing scheme was proposed based on the temperature-dependent intensity ratios of the emission lines from the thermally coupled and large Stark splitting levels of the 1D2 state. Relative sensitivities as a function of temperature were studied in the range of 93-473 K. The findings of this study indicate that Y3Si6N11:Pr3+ is an attractive broad-band red phosphor for both high color rendering white LEDs and temperature sensing applications.

Novel narrow band red emitters based on mixed metal oxides and their application in hybrid white light-emitting diodes

A series of high-efficiency narrow band red-emitting La₂ M₂ O₉ :Eu³⁺ (M = Mo/W) phosphors for white LEDs was synthesized using a conventional solid-state reaction method. All the compositions show absorption in the near ultraviolet (UV) light region due to charge transfer from O to M (M = W and Mo). In order to investigate the luminescence quenching effect, the Eu³⁺ concentration was varied in the La₂ M₂ O₉ lattice. The tungstate analogue had a quantum yield of 46.5%, whereas the molybdate equivalent had a comparatively subordinate value (15.4%). The phosphor could be competently excited by ~395 or 465 nm photons (could be integrated well with a near-UV or blue LED chip) and showed dominant red emission electric-dipole transition (⁵ D₀ →⁷ F₂ ) with sharp spectral lines due to 4f-4f electronic transition of the Eu³⁺ ion and potential red-emitting colour converters for white LEDs. The red LED was fabricated by integrating the best phosphor composition with a near-UV LED and a white hybrid LED was fabricated by conjugating with a yellow organic dye and a red phosphor with near-UV LEDs. The white hybrid LED showed an excellent colour rendering index (83%), with CIE colour coordinates (0.313, 0.365) and CCT (6280 K).

Crystal structure, luminescence properties and thermal stability of BaY2−xEuxGe3O10 phosphors with high colour purity for blue-excited pc-LEDs

The luminescence properties of reddish-orange emitting BaY_2−xEu_xGe₃O₁₀ phosphors crystallizing in the monoclinic system (S.G. P2₁/m) have been discussed in detail. The studied germanates are appropriate for applications in high-powered pc-LEDs.

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.