Green Phosphor Research Articles

Preparation and Luminescence Properties of SrLaAlO4:Tb3+ Green Phosphor

Preparation and Luminescence Properties of SrLaAlO4:Tb3+ Green Phosphor

Realizing full-spectrum LED lighting with a bright broadband cyan-green-emitting CaY2ZrGaAl3O12:Ce3+ garnet phosphor

Full-visible-spectrum white light-emitting diodes (LEDs) with ultrahigh color rendering index (CRI), which are capable of offering a light source that mimics natural sunlight, have great application potentials in healthy lighting, high-resolution displays, and plant growth lighting. However, cyan gap in the 480–520 nm wavelength range is commonly existed in the emission spectra of traditional phosphor-converted white LEDs, and thus it is urgent to develop high-performance cyan-emitting phosphors to close this spectral gap for realizing full-visible-spectrum LED lighting. Herein, we demonstrate a new efficient cyan-green-emitting Ce3+-activated CaY2ZrGaAl3O12 garnet phosphor for near-ultraviolet (near-UV) pumped full-visible-spectrum warm-white LEDs. The CaY2ZrGaAl3O12:Ce3+ cyan-green phosphor has a cubic structure with the space group Ia3‾d and lattice parameters of a = b = c = 12.39645(8) Å and V = 1886.08(6) Å3. Ce3+ doping concentration dependent luminescence properties have been studied, and the highest emission intensity is obtained at 1 mol%. The optimal CaY2ZrGaAl3O12:1%Ce3+ sample shows a broad excitation band in the 300–490 nm wavelength range with peak at 409 nm due to the 4f→5d transition of Ce3+ ions. Upon 409 nm excitation, CaY2ZrGaAl3O12:1%Ce3+ produces a wide cyan-green emission band in the 425–750 nm spectral range with a peak at 514 nm and a full width at half-maximum of 110 nm owing to the 5d→4f transition of Ce3+ ions, and the corresponding CIE color coordinates and internal quantum efficiency are determined to be (0.2802, 0.4856) and 56%, respectively. Furthermore, the resulting CaY2ZrGaAl3O12:1%Ce3+ phosphor exhibits good thermal stability, and its emission intensity at 423 K is about 58% of that at 303 K. Finally, a white LED device is fabricated by employing a 395 nm near-UV chip with the phosphor blend of commercial BaMgAl10O17:Eu2+ blue phosphor, as-prepared CaY2ZrGaAl3O12:1%Ce3+ cyan-green phosphor, commercial (Ba,Sr)2SiO4:Eu2+ green phosphor and commercial CaAlSiN3:Eu2+ red phosphor, which exhibits a bright full-spectrum warm-white light with low color correlated temperature of 3334 K and ultrahigh CRI values (Ra = 97, R9 = 95.3, R12 = 90.1) for 20 mA driving current. This work provides a new perspective in designing luminescent materials for high-color-quality full-visible-spectrum LED lighting.

Enhancing External Quantum Efficiency of Blue-Emitting Phosphor Ba(K)-β-Al2O3:Eu2+ by Lattice Site Engineering for Full-Spectrum Lighting.

The discovery of violet-excitable blue-emitting phosphor is a significant breakthrough for the development of phosphor-converted full-spectrum white light-emitting diodes (WLEDs). However, the application of most known violet-excitable blue-emitting phosphors is limited by their low external quantum efficiency (EQE). In this work, we reported on how the EQE values of Eu2+-doped Ba(K)-β-Al2O3 blue-emitting phosphor can be significantly improved through lattice site engineering. By partially substituting K+ for Ba2+, the Eu2+-occupied crystallographic site changes and the coordination polyhedron of Eu2+ shrinks, leading to the increase of crystal field splitting. Consequently, the excitation spectrum exhibits a continuous red shift to match the violet excitation, which enhances the PL intensity of solid solution phosphor (Ba0.4K1.6)0.84Al22O35-α:0.32Eu2+ ((B0.4K1.6)0.84AO:Eu) by 1.42 times compared to that of the end-member Ba1.68Al22O35-α:0.32Eu2+ (B1.68AO:Eu) phosphor. Correspondingly, under the 400 nm violet light excitation, the EQE of optimal blue-emitting (B0.4K1.6)0.84AO:Eu phosphor is up to 53%. Additionally, the phosphor also shows excellent resistance to luminescence thermal quenching (95% at 150 °C). Finally, the WLED fabricated based on (B0.4K1.6)0.84AO:Eu and commercial green and red phosphors exhibited an ultra-high color rending index with Ra = 95.5 and R1-R15 >90. This work offers guidance for tuning the spectral properties of phosphors through lattice site engineering.

Sunlight-Activated Long Persistent Luminescent Coating for Smart Highways

With the whole society’s demand for intelligence, the smart highway has become the inevitable trend of road development. Luminescent road marking made of long persistent luminescent coating is a new type of functional marking that is designed with long afterglow luminescent material as the raw material and has many features such as safety, beauty and energy saving. Here, SrA12O4:Eu2+,Dy3+ green long afterglow phosphors were prepared using a high-temperature solid state method. The green phosphors obtained at 1350 °C have two traps with a shallow trap depth of 0.66 eV and a deep trap depth of 0.8 eV. The green afterglow can be seen in the dark for more than 8 h after sunlight excitation for 2 h. The green long persistent luminescent coatings were synthesized using the blending method. The uniformity of each component can be improved by adding 1.25% SiO2 into the luminescent coatings. The addition of 3.5% CaCO3 will improve the compactness of the coatings and reduce water absorption. After soaking in water for 120 h, the afterglow intensity of the coating decreases to 76% of the original, showing good water resistance. After daylight excitation in different weather conditions (cloudy, sunny, rainy), the afterglow can reach more than 5 h; therefore, it can be applied to a smart highway.

Development of flexible luminescent films, photoluminescence properties and anti-counterfeiting applications of SrMoO4:Tb3+ green phosphors

Development of flexible luminescent films, photoluminescence properties and anti-counterfeiting applications of SrMoO4:Tb3+ green phosphors

Bright green emitter of Mn-doped C4H12N2ZnX4 (X = Cl, Br) for X-ray radiography and WLEDs

Zero-dimensional (0D) metal halides based on environmental friendliness, low cost, and earth-abundant elements have gained tremendous attention because of their applications including solid-state lighting, X-ray radiography, anti-counterfeiting labels and beyond. Herein, Mn-doped 0D C4H12N2ZnX4 (X = Cl and Br) with strong green emission has been developed in the application of the scintillator and the white light-emitting diode (WLED). Spectroscopic studies and density functional theory (DFT) calculations clarify the Mn doping effect on the electronic structure of C4H12N2ZnX4. The Mn doping reduces the bandgap owing to the Mn 3d contribution to VBM. The hybrid of Mn 3d orbitals with Br 4p/ Cl 3p enhances the Mn(II) d-d emission resulting in a maximum photoluminescence quantum yield (PLQY) of 99 % in Mn-doped C4H12N2ZnX4. Therefore, the WLED using Mn-doped C4H12N2ZnX4 as a green phosphor shows a high luminous efficacy of 98.52 lm/W and a CRI of 83.3, which is better than other similar WLEDs based on CsPbX3 or Mn-doped Cs2ZnX4. Impressively, Mn-doped C4H12N2ZnX4 ceramic wafer has X-ray radiography with 6–9 LP/mm spatial resolution better than CsI: Tl or MAPbI3.

Near-UV-excitable broadband green-emitting Ca2LaHf2GaAl2O12:Ce3+ garnet-type phosphors for high color rendering warm-white LEDs

Efficient broadband green-emitting phosphors are promising for application in high color rendering white light-emitting diodes (LEDs). In this paper, we report on the preparation, crystal structure and photoluminescence properties of a novel green-emitting Ca2LaHf2GaAl2O12:Ce3+ (CLaHGA) garnet-type phosphor. All these CLaHGA:xCe3+ (x = 4, 6, 8, 10, and 12 mol%) phosphors have been synthesized through using the conventional high-temperature solid-state reaction method. It has been found that the optical property of phosphors critically depends on Ce3+ content, and the optimal doping concentration of Ce3+ ions is 6 mol%. The optimal CLaHGA:6%Ce3+ sample has a cubic structure with the space group Ia3‾d and lattice parameters of a = b = c = 12.62662 Å and V = 2013.08 Å3. The CLaHGA:xCe3+ phosphors exhibit an intense absorption band in the 300–485 nm range with a peak at 421 nm, due to the spin-allowed and parity-allowed 4f→5d transition of Ce3+ ions. Upon 421 nm excitation, CLaHGA:xCe3+ phosphors give rise to bright broad green emission bands in the 435–750 wavelength region with peak ranging from 519 to 531 nm, owing to the spin-allowed and parity-allowed 5d→4f transition of Ce3+ ions. For the optimal CLaHGA:6%Ce3+ sample, its CIE color coordinates and internal quantum efficiency are determined to be (0.3135, 0.4851) and 40.7%, respectively. The full width at half maximum of CLaHGA:6%Ce3+ is much larger than the commercial (Ba,Sr)2SiO4:Eu2+ green phosphor (124 nm versus 71 nm), while its emission intensity is only about 39% of that of (Ba,Sr)2SiO4:Eu2+. Besides, the thermal stability of CLaHGA:6%Ce3+ has also been studied. A white LED device is fabricated using the synthesized CLaHGA:6%Ce3+ green phosphors, showing a bright warm-white light emission with high color rendering index of Ra = 89.7 and low correlated color temperature of 4058 K.

Improvement in luminescence of thermally stable CaMoO4:Tb3+ green phosphor by Bi3+ ions

The growing optoelectronic industries have prompted researchers to develop a single-component green phosphor for diverse applicability. It is well known that Tb3+ doped phosphors emit green light due to strong 5D4→7F5 transition. The green emission of Tb3+ ion can be enhanced by using sensitizers such as Bi3+ ion, which creates intermediate energy levels between the host and Tb3+, thereby, achieving efficient energy transfer between the host and Tb3+. In this article, we have reported a substantial improvement in the green emission of Tb3+ doped CaMoO4 by Bi3+ co-doping. The phosphors have been successfully prepared via a lucrative self-combustion process. The XRD patterns reveal an impurity-free tetragonal crystalline structure of all the phosphors. The Tb3+ doped CaMoO4 gives three major emissions at 489 nm, 544 nm and 621 nm corresponding to the Tb3+ transitions from 5D4 to 7F6, 7F5, and 7F3, respectively. The maximum emission has been achieved for 5% Tb3+ doped CaMoO4, which is further enhanced by 47% via co-doping of Bi3+. The improvement in emission intensity for Bi3+ co-doped phosphors is attributed to improved crystalline nature and transfer of energy from Bi3+ to Tb3+ levels. The energy transfer process from [MoO4]2- to Bi3+ and Tb3+ is explained in detail and maximum improvement is obtained upon co-doping of 4% Bi3+ ions. The incorporation of Bi3+ ions also results in shifting of CIE coordinates and color purity towards green color. The activation energy required for the thermal quenching is 0.25 eV, much better than already reported green phosphors. There is no change in the CIE coordinates of the overall emission with temperature indicating the better emission color stability of the phosphor. Hence with optimum concentration of Bi3+ and Tb3+ ion in CaMoO4 they can be used as potential green emitting phosphors.

A novel Ca2ScNbO6:Eu3+ phosphor with excellent thermal stability for high color rendering WLED

A series of novel Ca2-xScNbO6:xEu3+ double perovskite phosphors were synthesized by high-temperature solid-state reaction technique. The physical phase, micromorphology, photoluminescence properties, concentration and thermal quenching effect of the phosphors were analyzed. Research shows that: Ca2-xScNbO6:xEu3+ phosphors can be excited by ultraviolet or Blu-ray LED chips and displays a strong orange-red light luminescence at 614 nm. The sample with optimum doping concentrations has a quantum efficiency of 99.13% at room temperature, and the brightness only decays by 7.49% at 433 K. The sample has excellent thermal stability, with a thermal quenching extinction activation energy of 0.497 eV. Finally, the samples are packaged with 395 nm chips together with green and blue phosphors to obtain white LED, that emits bright white light under forward bias currents and have the advantages of lower correlated color temperature (less than 4390 K) and higher color rendering index (higher than 89). The above results indicate that Eu3+ ion-doped Ca2ScNbO6 phosphor can be applied to white LED technology.

Dazzling green luminescent and biocompatible Tb3+ -activated lanthanum tungstate nanophosphors for group-III evaluation of latent fingerprints and anticancer applications

Dazzling green emission exhibiting Tb3+ ions doped lanthanum tungstate (LWO) nanophosphors were synthesized by a facile hydrothermally assisted solid-state reaction method. The nanophosphors were determined to have an orthorhombic structure using XRD analysis. In the optimized Tb3+: LWO nanophosphor, FE-SEM revealed aggregated non-uniform nanorods. TEM, FTIR, and XPS studies were performed to examine the material properties. A predominant excitation band was recorded at 488 nm (7F6→5D4) for the Tb3+ doped LWO nanophosphors, along with a moderately intense excitation band at 378 nm (7F6→5G6). Ravishing green emission at 544 nm (5D4→7F5) was obtained from Tb3+ ions containing LWO nanophosphors under excitation at 378 nm and 488 nm. We improved the green emission intensity by increasing the Tb3+ ion concentration up to 14 mol%, which was reduced after 14 mol% due to concentration quenching. The energy-level diagram shows the green radiative transition pathway. The CIE coordinates and color purity were computed for Tb3+: LWO nanophosphors from their emission profiles, and the evaluated coordinates were centralized in the strong green region. A high color purity of 90.1% was obtained appreciably from the optimized Tb3+: LWO nanophosphor. The lifetime of the green emission transition was systematically evaluated based on decay dynamics. The visualization of fingerprints was examined using the optimized green phosphor with an in-depth analysis of the Group-III level details. The non-cytotoxicity of Tb3+ (14 mol%): LWO nanophosphor was confirmed in normal WI-38 lung fibroblast cells. Moreover, these phosphors exhibited strong cytotoxicity against human breast cancer cells of MCF-7. From these results, the synthesized Tb3+ (14 mol%): LWO non-cytotoxic nanophosphor material is considered the best green luminescent material for latent fingerprints in forensic investigation, photonic and anticancer applications.

Highly luminescent and thermostable R6G@DUT-52 composite for sensing Fe3+ ion and white light emitting diode

Introduction of the yellow rhodamine 6G (R6G) fluorescent dyes into the nanopores of DUT-52 has been successfully achieved the R6G@DUT-52 composite by the one-pot hydrothermal method. Its structure, stability and morphology are well characterized by the XRD, TGA and SEM, whose fluorescent properties are also studied in detail. The obtained R6G@DUT-52 exhibits the highly thermostability with the blue emission of the DUT-52 at 435 nm, the characteristic emission of R6G dyes at 568 nm and the highly quantum yields (QY) of 77.8%, which shows the potential application prospects as the probes for high selectivity and sensitivity of detecting Fe3+ ion from 12 kinds of metals ions. In addition, R6G@DUT-52 is cooperated with the commercial green phosphor powder (GGA) that is further encapsulated on the 455 nm blue LED chip to achieve the warm white light emitting diode (WLED) device with the CIE coordinates of (0.373, 0.364), correlated color temperature (CCT) of 4107 K and luminous efficiency (LE) of 113.08 lm/w.

Latest Advances in Narrow‐Band Phosphors and Their Role in Color Management

Latest Advances in Narrow‐Band Phosphors and Their Role in Color Management

A narrow-band RbBaBP2O8:Tb3+ green phosphor with high thermal stability for backlighting display application

A narrow-band RbBaBP2O8:Tb3+ green phosphor with high thermal stability for backlighting display application

A nitriding garnet structure cyan emitting phosphor Ca2(Y, Ce)Hf2(Al, Si)3(O, N)12 with high efficiency and excellent thermal stability

Cyan phosphors with high efficiency and excellent thermal stability are an important part for application in full spectrum illumination. Herein, a series of nitriding cyan emission phosphors Ca2(Y, Ce)Hf2(Al, Si)3(O, N)12 with garnet structure are successfully synthesized, their phase purity, crystal structure, morphology, elemental composition and valence state are analyzed in detail, and the results indicate that a small amount of Si3N4 doping does not cause impurity phase. The phosphor has an efficient broadband cyan emission at 493 nm with full width at half maximum (FWHM) of about 95 nm under 411 nm excitation. Impressively, the luminous intensity of the nitriding phosphor is increased by 30%, the internal/external quantum efficiency are increased from 41.63% and 40.01% to 61.93% and 52.13%, and the thermal stability is improved from 75%@150 oC to 85%@150 oC, which is even better than the commercial green phosphor LMS520B (77%@150 oC). Finally, a full-visible-spectrum LED with low correlated color temperature (CCT = 5143 K) and high color rendering index (Ra = 98.3) is fabricated by employing Ca2(Y, Ce)Hf2(Al, Si)3(O, N)12 phosphors as cyan emitting component. The results indicate that the nitriding Ca2(Y, Ce)Hf2(Al, Si)3(O, N)12 phosphors have potential to act as cyan emission phosphors for full-visible-spectrum LEDs.

Synthesis of yellow and green phosphors based on zinc orthosilicate doped by manganese at low temperature by impregnation – coprecipitation method

AbstractThis work studies the influence of magnesium concentration, sintering temperature, boric and acetic acid to synthesize yellow and green phosphors based on zinc orthosilicate doped by manganese at low temperature by a novel approach, the impregnation ‐ coprecipitation method. The samples were investigated by thermal analysis, luminescence spectroscopy, XRD, SEM and EDS. The results showed that the single‐phase zinc magnesium orthosilicate/borosilicate phosphors doped by manganese with rhombo. H. axes structure of α‐Zn2SiO4 were successfully synthesized when sintering corresponding precursors at 900°C for 45 minutes. Their luminescence efficiency is higher than that of the control samples prepared by coprecipitation method. The magnesium content for the maximum luminescence efficiency is 20 mol % per mol of metal ions. The highest luminescence product consists of spheroidal and relatively uniform particles with sizes around 0.6‐1.0 μm. The variation of the precipitated precursor with temperature, the influence of sintering temperature on structure and luminescence, the mineralization role of boric acid and the chemical reactions that occur with generation of precipitated precursors and upon heating to give luminescent solid solution products are mentioned.

Toward Ultra‐Broadband Absorption and High Quantum Efficiency Red Emission via Fluoride Single Crystals with Heavy Mn4+ Doping

AbstractOwing to the avoidance of device reabsorption and improvement in the color rendering index (CRI), Mn4+‐activated fluorides have potential applications in full‐spectrum lighting. However, it is still challenging to improve the external quantum efficiency (EQE) and adapt it to the excitation of violet‐light chips used for increasing the CRI and reducing the blue‐light hazard. Here, red‐light single crystals Rb2Si1−xMnxF6 (RSMF) with an ultrahigh optimal Mn4+ content of 32.4 mol% are obtained through structural and morphological design. Breaking through the limitation of low quenching concentration (<10 mol%) of Mn4+‐activated fluorides, the as‐grown heavy Mn4+‐doped RSMF crystal not only exhibits a record EQE of 80.2% but also has a broad excitation band of full width at half maxima = 86 nm, which can be efficiently excited by both blue (460 nm) and violet (437 nm) light. The white light‐emitting diodes fabricated by violet/blue dual‐chips, commercial green phosphor, and the optimized RSMF crystal can realize a high luminous efficacy of 161.8 lm W−1 and high CRI of Ra = 95.5. Additionally, laser diode devices with high luminous flux of 198.2 lm are also presented. This study provides new insights into heavy Mn4+‐doped materials and promotes the application of full‐spectrum lighting.

Antimony(III) based hybrid materials toward stable and highly efficient white LED

Zero-dimensional (0D) organic-inorganic hybrid materials have attracted extensive attention due to their facile preparation and excellent optical characteristics. However, achieving superior photophysical properties and excellent stability is still desirable for their practical application. Sb(III)-based metal halides owning 5 S2 lone-pair are prone to form deformable building units, which is beneficial for efficient self-trapped excitons (STE) emission. Herein, a 0D Sb(III)-based metal halides DIPA2SbCl5 (DIPA+ = 4-amino-3,5-diiodopyridin-1-ium) was obtained by solvothermal method at room temperature, which exhibited highly efficient broadband emission at 652 nm with a photoluminescence quantum yield (PLQY) of 87.1% and outstanding stability against moisture. Then, a white-light-emitting diode (WLED) was fabricated by mixing DIPA2SbCl5 with green phosphor ((Sr, Ba)2SiO4: Eu2+) and blue phosphor (BaMgAl10O17:Eu2+), with the CIE coordinates of (0.351, 0.371), a correlated color temperature of 4183 K and a color rendering index of 93.3. This work provides a universal solution to obtain hybrid materials with efficient luminescence properties and potential applications.

Potential application of Eu3+ ion-activated Ca2InTaO6 red phosphor with high thermal stability in WLEDs

The high-temperature solid-phase method synthesized a series of red phosphors Ca2InTaO6: xEu3+. Their most substantial emission peak is at 612 ​nm, FWHM ​= ​8 ​nm, and they can be excited under blue light. Has very excellent thermal stability, still has 77.7% of normal emission intensity at 150 ​°C, and the luminous intensity decreases very slowly between 80 ​°C–150 ​°C. In the high temperature durability test at 120 ​°C and 150 ​°C, the sample can still maintain good luminous intensity for a long time. The WLED was fabricated using fabricated samples in combination with commercial green and blue phosphors; it has Ra ​= ​90.1 and R9 ​= ​83.4. All expected test results prove that this sample is suitable for modern LED lighting.

Research on advancing chromatic reproduction and luminosity of a WLED using triple-layer remote phosphor arrangement

In this study, the use of triple-sheet phosphor arrangement (TRP) in performing significant improvements to both color quality and luminous flux of white light emitting diode (WLEDs) is introduced. The phosphor layer of CaLaB3O7:Ce3+,Mn2+ is to accomplish green-spectra enhancement for the boost of luminous efficacy (LE), while MgB2O4:Mn2+ red phosphor layer is for red-spectra enhancement to better color rendering index (CRI) of WLEDs. The changes in these two phosphors’ concentrations present considerable effects on the yellow phosphor YAG:Ce3+ concentration, the color quality scale (CQS), CRI, and LE. Findings display the decrease of YAG:Ce3+ concentration accompanying the increase of red and green phosphor concentrations, for the stabilized average correlated color temperatures (ACCTs) between 6000 and 8500 K. Results also reveal that greater content of MgB2O4:Mn2+ leads to greater CRI value. Meanwhile using the increasing CaLaB3O7:Ce3+,Mn2+ concentration, the CRI lowers considerably. CQS, on the other hand, can increase with CaLaB3O7:Ce3+,Mn2+ concentration from 10% to 14%. Especially, given the enhancement for the CRI as well as CQS, LE value will surge to more than 40% due to the reduction of scattering light and the addition of green light. The outcome of the study is a priceless reference for light emitting diode (LED) producers.

Persistent Luminescence Zn2GeO4:Mn2+ Nanoparticles Functionalized with Polyacrylic Acid: One-Pot Synthesis and Biosensing Applications.

Zinc germanate doped with Mn2+ (Zn2GeO4:Mn2+) is known to be a persistent luminescence green phosphor with potential applications in biosensing and bioimaging. Such applications demand nanoparticulated phosphors with a uniform shape and size, good dispersibility in aqueous media, high chemical stability, and surface-functionalization. These characteristics could be major bottlenecks and hence limit their practical applications. This work describes a one-pot, microwave-assisted hydrothermal method to synthesize highly uniform Zn2GeO4:Mn2+ nanoparticles (NPs) using polyacrylic acid (PAA) as an additive. A thorough characterization of the NPs showed that the PAA molecules were essential to realizing uniform NPs as they were responsible for the ordered aggregation of their building blocks. In addition, PAA remained attached to the NPs surface, which conferred high colloidal stability to the NPs through electrostatic and steric interactions, and provided carboxylate groups that can act as anchor sites for the eventual conjugation of biomolecules to the surface. In addition, it was demonstrated that the as-synthesized NPs were chemically stable for, at least, 1 week in phosphate buffer saline (pH range = 6.0-7.4). The luminescence properties of Zn2GeO4 NPs doped with different contents of Mn2+ (0.25-3.00 mol %) were evaluated to find the optimum doping level for the highest photoluminescence (2.50% Mn) and the longest persistent luminescence (0.50% Mn). The NPs with the best persistent luminescence properties were photostable for at least 1 week. Finally, taking advantage of such properties and the presence of surface carboxylate groups, the Zn2GeO4:0.50%Mn2+ sample was successfully used to develop a persistent luminescence-based sandwich immunoassay for the autofluorescence-free detection of interleukin-6 in undiluted human serum and undiluted human plasma samples. This study demonstrates that our persistent Mn-doped Zn2GeO4 nanophosphors are ideal candidates for biosensing applications.