Red-emitting Phosphor Research Articles

Synthesis, crystal structure, and characterizations of Eu3+-activated Ca2LnHf2(AlO4)3 (ln = Lu, Y and Gd) red-emitting phosphors for phosphors-converted white LEDs

High-brightness red-emitting Ca2LnHf2Al3O12:Eu3+ (Ln = Lu, Y and Gd) garnet phosphors with high photoluminescence efficiency are demonstrated for application in white light-emitting diodes (LEDs), and they have been successfully prepared using a high-temperature solid-state method. X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping, photoluminescence excitation and photoluminescence spectra, decay lifetimes, photoluminescence quantum yield and temperature-dependent emission spectra have been used to characterize these samples. Under near-ultraviolet excitation into the 7F0→5L6 transition of Eu3+ at 394 nm, the Ca2LnHf2Al3O12:Eu3+ (Ln = Lu, Y and Gd) samples produce the characteristic red emissions of Eu3+ ions with peaks around 591, 611, 656, and 709 nm, corresponding to the 5D0→7F1, 5D0→7F2, 5D0→7F3, and 5D0→7F4 transitions. These samples exhibit significant concentration-dependent luminescence behaviors, and the highest emission intensity is achieved at 50 mol% Eu3+ doping concentration owing to the concentration quenching effect caused by the dipole-dipole interaction between neighboring Eu3+ activators. The CIE color coordinates of these optimal Ca2LnHf2Al3O12:50%Eu3+ (Ln = Lu, Y and Gd) phosphors are (0.6339, 0.3654), (0.6341, 0.3653), and (0.6343, 0.3651), along with respective color purity of 92.4%, 92.6%, and 92.6%. The photoluminescence quantum yields of Ca2LnHf2Al3O12:50%Eu3+ are determined to be 39.2%, 56.6%, and 53.3% for Ln = Lu, Y, Gd, respectively. A white LED device has been fabricated through utilizing the Ca2YHf2Al3O12:50%Eu3+ phosphor as red-emitting color converter, which generates bright warm-white light with high color rendering index (80.8), low correlated color temperature (3920 K), CIE chromaticity coordinates (0.3827, 0.3742), and high luminous efficacy (11.56 lmW−1) under 40 mA driving current.

Comparative investigation on luminescence properties of red-emitting KLiSnF6:Mn4+ phosphors and the fluorescent sheet for high-power LEDs

New red-emitting phosphors KLiSnF6:xMn4+ (KLSFM, x = 4%, 6%, 8%, 10%, and 12%) for LED lighting were synthesized by an ion-exchange method at room temperature. Among these phosphors, the KLSFM (8 mol%) sample exhibits the strongest excitation in the blue region and emission in the red region. The corresponding translucent fluorescent sheet prepared by the pressure method shows similar luminescent properties which are identical to the powders with the strongest absorption at 467 nm and narrow emission around 632 nm. The fluorescent sheet offers high transmittance in UV–Vis region (close to 100% beyond 550 nm) and better thermal stability and color stability. For comparison, the white pc-LEDs based on the KLSFM (8 mol%) phosphor and fluorescent sheet all emit intense white light with an ideal color rendering index (CRI >93) and a good correlated color temperature (CCT <3500 K). However, the white pc-LED based on the fluorescent sheet have more advantage in application for high-power devices. Working at 200 mA, the LED fabricated with the translucent sheet still keeps excellent performance with a high CRI of 90.1 and a low CCT of 3874 K. The working temperature for this device is only 90 °C after working for 40 min, which is lower than that of the device with the KLSFM (8 mol%) powder, furtherly proving that the translucent sheet has excellent heat dispersion. Therefore, the KLSFM (8 mol%) translucent sheet could be used for high-power pc-LEDs as a red component.

Structure, photoluminescence, Judd-Ofelt analysis, and thermal stability studies of Eu3+-doped Ba2Tb8(SiO4)6O2 red phosphor with high color purity

In this study, a series of Eu3+-doped Ba2Tb8(SiO4)6O2 red-emitting phosphors were developed by using a conventional solid-state reaction technique. The crystalline structure, surface morphology, photoluminescence properties, energy transfer processes, and thermal behavior of the Eu3+-doped Ba2Tb8(SiO4)6O2 phosphors were studied. The X-ray diffraction patterns confirmed the formation of the phase, and the Rietveld refinement study revealed that the Eu3+-doped Ba2Tb8(SiO4)6O2 phosphors have a hexagonal crystal structure with the space group P63/m. Energy-dispersive X-ray analysis confirmed the homogenous distribution of Eu3+ ions over the Tb3+ sites. Photoluminescence (PL) spectroscopy was used to test the luminescent properties of the synthesized phosphors. The PL spectra showed that upon UV and blue light exposure, the Eu3+-doped Ba2Tb8(SiO4)6O2 phosphors exhibited red emission associated with the 5D0→7FJ transitions. The mechanisms of concentration quenching and energy transfer were analyzed using Blasse and Dexter's formula. Judd-Ofelt parameters (Ω2, Ω4) and other radiative parameters were analyzed using PL emission spectra to investigate the luminescence behavior of Eu3+-doped Ba2Tb8(SiO4)6O2 phosphors. The results of the thermal stability studies show that Eu3+-doped Ba2Tb8(SiO4)6O2 has good thermal properties with a high activation energy of approximately 0.23 eV. The calculated Commission International del'Eclairage coordinates (x = 0.62 and y = 0.36) of the prepared phosphors confirm that the emitted light is in the red portion with a high color purity of about 99.9%. These findings show that Eu3+-doped Ba2Tb8(SiO4)6O2 phosphors are a viable option for solid-state lighting technology.

Fluorescence properties and thermal stability of Sr2Gd1-xNbO6: xEu3+ with dual-wavelength excitation response

A series of double perovskite-type Sr2Gd1-xNbO6: xEu3+ (x = 0.04–0.12) red-emitting phosphors were successfully synthesized by a solid-state high-temperature sintering reaction, and the microstructure and luminescent performance of the phosphor are investigated in detail. The red-emitting phosphor has a monoclinic crystal structure with a space group of P21/c. The optimal concentration of the Eu3+ dopant in the Sr2GdNbO6 host was 0.08. Under dual-wavelength excitation of λex = 468 nm and λex = 395 nm, phosphor emits a red-orange color, and the principal emission peaks are located at 622 nm and 593 nm, which correspond to the 5D0→7F2 and 5D0→7F1 energy level transitions of Eu3+, respectively. Under the excitation of blue light λex = 468 nm, the phosphor exhibits not only a greater thermal stability but also a high luminescence color purity (93%). It is a new potentially red-emitting phosphor with dual wavelength excitation responsiveness.

A novel narrow-band red-emitting multi-layer phosphor for white – Light emitting devices

SrZr2La2O7: Eu+3 (0.5–2.5 mol %) phosphors have been synthesized through the standard solid-state reaction technique. The photoluminescent and other structural properties such as PXRD (Powder X-ray Diffraction), SEM (Scanning Electron Microscopy) and Energy Dispersive X-ray spectroscopy (EDX), FTIR (Fourier transform infrared spectroscopy), PSD (Particle Size Distribution) of the phosphors were learned. The photoluminescence spectra show that the phosphor exhibited intense and dominant red emissions at 627 nm belonging to the 5D0 → 7F2 electric dipole transition. The FWHM of the red emissions at 627 nm is only 8.0 nm increasing in luminous efficacy. Hereby we propose a novel RED phosphor for RED emitting LEDs with phosphor-embedded polymer matrix layers of variable thickness and stacking up to 400 µm. The intensity of the red color was enhanced by self-excitation of photon absorption and emission. As a result, Eu3+doped SrZr2La2O7 phosphors can be widely used as red phosphors in UV chip-based WLEDs and displays. The phosphor exhibits high color purity up to 99% when excited at 590 nm. X-ray powder diffraction analysis confirms that the phosphor is highly crystalline and has a cubic phase.

Structure, properties and application of Eu3+ doped bismuth molybdate red-emitting phosphor synthesized by sol-gel method

In this work, red-emitting Eu3+ doped bismuth molybdate phosphors (BMO: Eu3+) were synthesized by a sol-gel method. The influences of calcination temperature on BMO: Eu3+ were investigated. The structure and properties of BMO: Eu3+ at different calcination temperatures were characterized by XRD, Raman, SEM, FT-IR and PL techniques respectively. The crystal structure and related parameters were obtained by a Rietveld method. The relationship between the luminescence performance and the crystal structure is analyzed in detail. Furthermore, the BMO: Eu3+ phosphors was applied to the preparation in luminescent films and LED devices. In addition, it was the first time that BMO: Eu3+ phosphors were applied to the detection of Fe3+, Cr2O72− and 4-Nitrophenol (4-NP). It is worth noting that it has good selectivity and sensitivity to 4-NP, Fe3+ and Cr2O72−, which can be used as luminescent sensors for detection. Among them, the LOD of 4-NP is as low as 2.32 μM.

Synthesis and photoluminescence characterisation of Ca2La2O5:Eu3+, a novel red-emitting phosphor: a comprehensive study

ABSTRACT A novel low-melting-temperature chemical flux method was used to synthesise a Ca2La2O5 lattice doped with Eu3+ ions in the range of 0.5-2.5 mol-%. The phosphors were characterised by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, particle size distribution, photoluminescence (PL), and Fourier transform infrared spectroscopy, respectively. The PXRD pattern revealed the hexagonal crystal structure with the space group P63/m. The microstrain (ϵ) was found to not vary with different concentrations of dopant and the negative means compression in the lattice. Particles of varying sizes and irregular shapes were observed from the SEM micrographs. The EDAX mapping revealed that all the constituent elements were found to be in appropriate ratios. Interestingly, the Ca2La2O5:xEu3+ (x = 0.5-2.5 mol-%) phosphor samples were excited at 590 nm, showing a Stokes-shifted red-PL with significant intensities at 615 and 627 nm. Unconventionally, when the phosphor is excited at 590 nm, the Eu3+ ion-characteristic luminescence owing to 5D0→7FJ (J = 0, 1, 2, 3, 4) transitions are manifested. Another remarkable observation is that the PL at 627 nm corresponding to 5D0→7F3 transition was much stronger than the 615 nm emission of Eu3+ corresponding to 5D0→7F3 transition, indicating high colour purity among the available red-emitting phosphors.

Tunable luminescence and energy transfer in Tb3+,Eu3+ co-doped Gd2Zr2O7 phosphors with high thermal stability for WLEDs

Red phosphors with good thermal stability, high color temperature and color purity are critical in high power warm white LED devices. Herein, a series of single and co-doped Tb3+,Eu3+ polychromatic phosphors with pyrochlore structure based on Gd2Zr2O7 have been prepared for the first time by a conventional solid phase reaction method. Compared to single doped Eu3+ phosphors, Tb3+,Eu3+ co-doped phosphors possess following advantages: improved UV absorption, increased photoluminescence intensity, extended luminescence range and improved thermal stability. At room temperature, the Gd2Zr2O7:Tb3+,Eu3+ phosphors exhibited a gradual shift from yellow-green emission at 544 nm to orange-red emission at 613 nm with increasing doping of Eu3+ ions. Energy transfer efficiency has been evaluated to be 71% by analyzing the fluorescence lifetime of Tb3+ ions. The concentration quenching mechanism under different conditions was analyzed in detail and it was concluded that the quenching of Tb3+ is caused by dipole-dipole interaction. In addition, the activation energy (ΔEa) of the Gd1.92Zr2O7:0.03Tb3+,0.05Eu3+ phosphor was calculated to be as high as 0.2674 eV compared to other Tb3+, Eu3+ co-doped phosphors, demonstrating its high thermal stability. WLEDs devices based on Gd1.92Zr2O7:0.03Tb3+,0.05Eu3+ phosphors have been prepared, which have low correlated color temperature (CCT) (5283 K), high color rendering index Ra = 85.5 K) and CIE coordinates chromaticity coordinate (0.3371,0.3333). All of the results show that Gd2Zr2O7:Tb3+,Eu3+ phosphors provide a new avenue to develop high quality red emission and high thermal stability phosphors for WLEDs.

Luminescence studies of high color purity red-emitting [formula omitted] phosphor prepared by microwave-assisted synthesis technique

A set of red-emitting phosphor materials (Ca1−xAl4O7:Eux3+, x = 0, 0.01, 0.03, 0.05, 0.07, 0.09, 0.11, 0.13) were synthesized through microwave-assisted combustion synthesis for the first time. The crystal structures and phase purity of Eu3+ ions-activated calcium dialuminate (CaAl4O7) phosphor were investigated by XRD study and Rietveld refinement analysis were performed. The prepared phosphors exhibit monoclinic crystal structure having C2/c space group. From the radius difference percentage calculation, the occupancy of Eu3+ ions in Ca2+ sites was confirmed which is in better harmony with the refinement result. Morphological analysis was investigated through SEM study. Structural characteristics and the presence of the functional groups were analysed though FTIR study. The optical band gap (Eg) was determined to be 5.46 eV by studying the UV–VIS reflectance spectra. PL measurements were carried out for the prepared material to study the luminescent behaviour. The presence of charge transfer band was observed in the excitation spectra. It is found that the prepared phosphor materials exhibits emission rich in red at 611 nm with fixed excitation wavelength at 393 nm. The concentration quenching and energy transfer kinetics were analysed by employing Blasse and Dexter’s formula that attributed the non-radiative energy transfer to the dipole-dipole (d-d) interactions. Local site symmetry was analysed to study the symmetry of the environment in the neighbourhood of Eu3+ ions in the host matrix. To analyse the colorimetric performance of the phosphor materials, the correlated color temperature (CCT), color purity were calculated by using the CIE chromaticity co-ordinates (CIE 1931). The calculated CCT value shows the appearance of the emitted color of the phosphor in the warmer region. CaAl4O7:Eu3+ phosphor manifests high color purity which was found to be 97.39 %. The PL decay time measurement were performed for Ca1−xAl4O7:Eux3+ (x = 0.07) phosphor to obtain the decay lifetime. The estimated decay time (1.44 ms) indicates that the prepared phosphor material has a good potency to be utilized as a red-emitting phosphor for wLED, display technology and other applications.

Ion exchange-promoted surface reduction strategy: For improving the water-resistance of K2SiF6:Mn4+ red phosphors

Mn4+-doped fluoride red emission phosphors with excellent luminescence properties have become an important part of white light-emitting diodes (WLEDs), but the poor moisture resistance of the phosphors hinders their practical application. Aiming to solve this problem, this paper proposes an ion exchange-promoted surface reduction (IESR) strategy in which K2SiF6:Mn4+ (KSF: Mn4+) phosphor is treated with NaNO2 in a mixed solution of NH4F/HCl, and a thick and clean Mn4+-free shell layer is constructed on its surface to improve water resistance. The thickness of the Mn4+-free shell layer of the optimal sample is determined to be about 600 nm by focused ion beam (FIB) and scanning electron microscope (SEM) characterization techniques. The internal quantum yield (QYi) of the treated phosphor (IESR-KSF:0.05Mn4+) is 88.86%, and it maintains a high QYi (75.69%) under the extreme hydrolysis environment of high temperature and high humidity, which is better than the results treated by the reverse cation-exchange strategy (22.81%) and the surface passivation strategy (7.9%). Moreover, IESR-KSF:0.05Mn4+ has a strong negative thermal quenching (NTQ) effect, which could be attributed to the electron-phonon interaction mechanism. The LED device encapsulated with the phosphor is aged at 85 °C and 85% relative humidity, and the results demonstrate that the IESR strategy can effectively improve the luminescence stability of fluoride phosphors.

Development of a novel Eu3+-doped tantalate red-emitting phosphor for w-LEDs application

Two novel phosphors LiBa4(1‒x)Eu4xTa3O12 (H-LBTO:xEu3+) and Li0.25Ba1‒xEuxTa0.75O3 (C-LBTO:xEu3+) were prepared successfully by a molten salt method. The transformation between these two structures was realized by changing the sintering temperature or changing the Eu3+ ions concentration, which was also demonstrated by the X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectra (DRS), and photoluminescence excitation (PLE) analyses. Both the sintering temperature and the Eu3+ ions doping concentration have significant impact on the formation of the crystal phase. All these phosphors sintered at 1023 K exhibit two major luminescence lines at 594 and 614 nm under near-UV light of 395 nm excitation, corresponding to Eu3+ ions typical transitions of 5D0→7F1 and 5D0→7F2. The optimum concentration of Eu3+ ions is 9 mol% for C-LBTO:xEu3+ samples and the quenching interaction type is the nearest-neighbor ion interaction. The thermal stability of the C-LBTO:0.09Eu3+ sample was investigated in detail and the device application further suggests that C-LBTO:0.09Eu3+ can be used as a red phosphor for near-UV excited w-LEDs in lighting.

Photoluminescence enhancement and excellent thermal stability of Ca2ZnSi2O7:Pr3+ red-emitting phosphors through charge compensator A+ (Li+, Na+ and K+) co-doping for w-LED applications

The red-emitting Ca2ZnSi2O7:Pr3+ phosphor was synthesized via a solid-state method and alkali metal ions A+ (Li+, Na+, K+) were introduced to improve the photoluminescence performance of Pr3+. XRD results confirmed that the sample structure did not change markedly with appropriate Pr3+/A+ co-doping. Under the blue light excitation of 447 nm, the as-prepared Ca2ZnSi2O7:Pr3+ efficiently emitted a characteristic red luminescence peak at 601 nm. The luminescence intensity of Pr3+ was obviously enhanced with A+ co-doping due to the charge compensation effect and the emission intensity of Ca2ZnSi2O7:0.005Pr3+, 0.005Na+ reached 142.1% compared to Ca2ZnSi2O7:0.005Pr3+. Furthermore, at 210 °C the luminescence intensity of the Ca2ZnSi2O7:0.005Pr3+, 0.005Na+ phosphor remained at ∼93% compared to at 30 °C, showing high thermal stability. The w-LED device packaged with Ca2ZnSi2O7:0.005Pr3+, 0.005Na+ produced a bright white emission. All these results indicated the potential application prospects of red-emitting Ca2ZnSi2O7:Pr3+, A+ phosphors in the field of white light-emitting diodes.

Bi3+ sensitizer induced efficient deep-red luminescence in Mn4+-doped 4SrO‧7Al2O3 toward the applications of plant growth lamp

In the natural environment, light is an indispensable factor affecting plant growth, and plant growth phosphor-converted light emitting diodes (pc-LED) for an artificial light source can play a role in accelerating photosynthesis and development of indoor plants. In this work, we obtained a series of red-emitting phosphors Bi3+, Mn4+ co-doped 4SrO‧7Al2O3, which were synthesized by sol–gel method, and red-light emission enhancement through doping of sensitizer Bi3+. The energy transfer process and mechanism were analyzed by photoluminescence spectra and fluorescence lifetime. And it thermal stability was 58.50% at 423 K, which show that the phosphor has good photostability. The red and blue dual emission of the packaged LED device can better match the absorption spectra required by chlorophyll a, b and phytochrome PR of plants. Therefore, the as-prepared phosphor has a certain development prospect in the application of plant growth LEDs.

Highly bright broadband cyan-emitting CaLu2HfGaAl3O12:Ce3+ garnet phosphors for high-color-quality white light-emitting diodes

In this work, novel highly efficient cyan-emitting Ce3+-activated CaLu2HfGaAl3O12 (abbreviated as CLHGAO) garnet-structured phosphors were synthesized using the high-temperature solid-state reaction route. Rietveld refinement results demonstrate the as-prepared samples belong to cubic space group Ia3‾d. These CLHGAO:xCe3+ (x = 0.5–8%) phosphors possessed a broad absorption band in the 320–450 nm wavelength range with a maximum at 408 nm. Upon 408 nm excitation, the CLHGAO:0.5%Ce3+ sample showed a broad cyan emission band within 425–750 nm wavelength range (emission peak: 493 nm; bandwidth: 95 nm), along with CIE color coordinates of (0.1939, 0.3533) and a high internal quantum efficiency of 81.9%. It is observed that, with increasing Ce3+ doping concentration from 0.5% to 8%, the emission peak position of CLHGAO:xCe3+ moves from 493 nm to 527 nm, and the corresponding emission color changes from cyan to green. Besides, the thermal stability and color stability of CLHGAO:0.5%Ce3+ phosphor at high temperature are also studied. A white LED device was fabricated by utilizing a 395 nm LED chip with as-prepared CLHGAO:0.5%Ce3+ cyan-emitting phosphor and commercial (Ba,Sr)2SiO4:Eu2+ green-emitting phosphor and commercial CaAlSiN3:Eu2+ red-emitting phosphor, and it demonstrates a high-color-quality white light with high color rendering index of 91, low color correlated temperature of 3547 K and good luminous efficacy of 58.71 lmW−1.

One-step modified combustion synthesis of yttrium aluminum borate phosphor doped with europium for long lasting solid-state lighting

The red-emitting phosphor YAl3(BO3)4: Eu3+(Yttrium Aluminum Borate) is synthesized by a simple, time-saving, economical novel method of solution combustion synthesis at 500 °C, a comparatively lower temperature using urea and glycine as fuel. In this work, the phosphor YAl3(BO3)4: Eu3+ is synthesized for the first time in one step at 500 °C by the combustion method. Europium as a doping in Yttrium Alunium borate phosphor gives intense emission in the red region having a prominent emission band at 614 nm with the excitation at 395 nm. This excitation band at 395 nm makes phosphor, a good red emitter for the n-UV LED for making w-LED for solid-state lighting. The phosphor YAl3(BO3)4: Eu3+ was also investigated for long-lasting or persistent luminescence for the first time. We observed long-lasting emission in the YAl3(BO3)4: Eu3+phosphor treated in reducing atmospheres, upon UV irradiation (254 nm) using emission from a Xe lamp (Hitachi F-7000).

Luminescent analysis of [Eu2DPA3] MOF as high purity red-emitting phosphor with thermal stability

In this work, the synthesis of a red-emitting phosphor with thermally stable photoluminescence, [Eu2DPA3]n MOF is reported. Thermogravimetric analysis (TGA) confirmed the formation of the coordination polymer with 2:3 metal to ligand stoichiometry, without water contents. Fourier transform infrared spectroscopy (FTIR) evidenced bands corresponding to different coordination modes between DPA carboxylates and pyridine nitrogen atoms with the Eu3+ ion, among them were COOEu, COOEu2, COOEu3, as well as picolinic mono- and bis-chelates, clearly indicating the formation of a coordination polymer. The luminescent properties were determined using 300 and 395 nm as exciting wavelengths, getting the typical emission bands of Eu3+ (5D0 →7F0,1,2,3,4). Luminescence lifetimes (τ) were determined using a monoexponential fit obtaining values of 2.2 (λexc = 300 nm) and 1.9 ms (λexc = 395 nm). The [Eu2DPA3]n MOF shows quantum efficiency of 48% (λexc = 300 nm) and 42% (λexc = 395 nm), and an absolute quantum yield of 55 and 31% with the same excitation conditions. The photometric study indicates that the luminescent response to excitation with 300 and 395 nm is practically identical, with a high purity red color >98%, and a chromatic coordinate of 0.65, 0.35. The temperature-dependent luminescence properties revealed a stable luminescent signal in the range of 30–150 °C, with a signal loss of 3.5% and an extinction energy (ΔE) of 0.21 eV.

A new Na2BaCa(PO4)2: Eu3+ red-emitting phosphor with excellent thermal stability and high quantum efficiency for WLEDs

A series of new red phosphors Na2BaCa(PO4)2: xEu3+ was synthesized by the high temperature solid phase reaction method. Through employing X-ray diffraction, scanning electron microscope, photoluminescence spectroscopy, quantum efficiency curves and high-precision rapid spectrometers, a systematic investigation was conducted on the microstructure and optical characteristics of the material. The XRD analysis of Na2BaCa(PO4)2: xEu3+ shows the sample to be a pure phase. The spectroscopic results show the presence of a red emission peak originated from 5D0 → 7F2 transition, and the quenching mechanism is attributed to interaction between nearest neighboring ions. Under 423 K, the fluorescence intensity of Na2BaCa(PO4)2: 0.2Eu3+ phosphor can still maintain 94.82 % of the value observed at 298 K, and the thermal activation energy ΔE reaches up to 0.3543 eV. The CCT of the LED packaged with Na2BaCa(PO4)2: 0.2Eu3+ was measured to be 4314 K, with the CIE coordinates (0.3658, 0.3600), which is very close to the point of standard white light source. The quantum efficiency of Na2BaCa(PO4)2: 0.2Eu3+ was measured to be 82.92 %. All results indicate that Na2BaCa(PO4)2: 0.2Eu3+ is suitable for WLED applications.

Achieving chip-matched high purity red emission by Bi3+ sensitization in Ca3MgTiGe3O12:Pr3+

Phosphor-converted light emitting diodes (pc-LEDs) are essential for current lighting and display areas because of their unique properties of being uncomplicated, durable and economical. In previous studies, Pr3+ doped red-emitting phosphors have attracted enormous research interest due to their high color purity. However, their photoluminescence excitation (PLE) spectra are always hard to be combined with LED chips. This mismatch is a great obstacle to achieve Pr3+ phosphors utilizing in LED devices. Here, to circumvent this issue, Pr3+-doped Ca3MgTiGe3O12 (CMTG) red-emitting phosphor was optimized with PLE band shifting from 330 nm to 360 nm after tuning with Bi3+ co-doping based on the structure and phosphorescence properties. The chip-matched excitation makes it a good candidate for white LEDs (wLEDs) fabrication to improve the output quality of device. Meanwhile, the high color purity of 93.02 % was obtained, which is conducive to widening the color gamut of backlight display applications. The photoluminescence (PL) spectra, fluorescence lifetime, and X-ray photoelectron spectroscopy (XPS) analysis were employed and discussed in detail to explain the role of Bi3+ played in the system. Finally, wLEDs were fabricated with CMTG:Pr3+, Bi3+, showing a high color rendering index (Ra) of 94.4. And the color gamut covers ∼80 % of the National Television System Committee (NTSC) standard, suggesting great potential for applications of wLEDs and backlight display.

Efficient lifetime-based optical thermometry using BaLaZnSbO6:Mn4+ red-emitting phosphors

In this study, a series of Mn-doped BaLaZnSbO6 (BLZSO:Mn4+) phosphors were synthesized by solid-state reaction method. Under 355 nm excitation, the BLZSO:Mn4+ phosphors exhibited a red emission with the peak centered at 697 nm, which was attributed to the 2Eg → 4A2g characteristic transition of Mn4+ ions. The optimal doping concentration of Mn4+ was found to be 0.6% and the concentration quenching mechanism was attributed to dipole-dipole interaction. Moreover, the structural information, crystal field strength, color purity and thermal stability were studied in detail. Additionally, the temperature-dependent lifetime of Mn4+ ions was monitored in the temperature range of 13–473 K and the maximum Sr value was obtained to be as high as 1.87 K-1. This work reveals that the BLZSO:Mn4+ phosphors have potential in the field of optical thermometer.

Creation of Dual Thermally Activated Delayed-Fluorescence Exciplexes in a Bulk Emitting Layer and Its Interface with an Electron Transport Layer for Promoting the Performance of Thermally Activated Delayed-Fluorescence Organic Light-Emitting Diodes Fabricated by a Solution Process.

An exciplex, which is composed of electron donor and acceptor molecules and formed by intermolecular charge transfer, is an excited-state species that is able to emit light or transfer its energy to a lower-energy emitter. In reported exciplex-based organic light-emitting diodes (OLEDs), their working mechanism is to generate exciplexes either in the bulk emitting layer (bulk exciplex) or at its interface with an electron transport layer (interface exciplex); both types give promising device performance. Here, we propose a novel strategy of creating both types of exciplexes simultaneously (dual exciplexes) for the generation of more exciplexes for better device performance as indicated in the improved photoluminescence quantum yield (PLQY). Impressively, the dual exciplex-based device with blue thermally activated delayed fluorescence (TADF) emitter 9,9-dimethyl-9,10-dihydroacridine-2,4,6-triphenyl-1,3,5-triazine (DMAC-TRZ) exhibits a record-high maximum external quantum efficiency (EQEmax) of 26.7% among the solution-processed TADF blue OLEDs. By further doping with the red-emitting phosphor emitter into the EML, the white device also gives a record-high EQEmax of 24.1% among the solution-processed TADF-phosphor hybrid white OLEDs (T-P WOLEDs) with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.34, 0.42), color rendering index of 70, and correlated color temperature of 5198 K. Furthermore, both blue and white devices show an ultralow efficiency roll-off with external quantum efficiencies at a practical brightness value of 1000 cd m-2 (EQE1000) of 25.1 and 23.9%, respectively. This is the first report of employing a dual exciplex-based OLED with excellent device performance.