Strategies to approach high performance in Cr3+-doped phosphors for high-power NIR-LED light sources.
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ABSTRACT:
SUBMITTER: Jia Z
PROVIDER: S-EPMC7229223 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Mn4+-activated hexafluoroaluminates are promising red-emitting phosphors for white light emitting diodes (w-LEDs). Here, we report the synthesis of Na₃AlF₆:Mn4+, K₃AlF₆:Mn4+ and K₂NaAlF₆:Mn4+ phosphors through a simple two-step co-precipitation method. Highly monodisperse large (~20 μm) smoothed-octahedron shaped crystallites are obtained for K₂NaAlF₆:Mn4+. The large size, regular shape and small size distribution are favorable for application in w-LEDs. All Mn4+-doped hexafluoroaluminates show bright red Mn4+ luminescence under blue light excitation. We compare the optical properties of Na₃AlF₆:Mn4+, K₃AlF₆:Mn4+ and K₂NaAlF₆:Mn4+ at room temperature and 4 K. The luminescence measurements reveal that multiple Mn4+ sites exist in M₃AlF₆:Mn4+ (M = Na, K), which is explained by the charge compensation that is required for Mn4+ on Al3+ sites. Thermal cycling experiments show that the site distribution changes after annealing. Finally, we investigate thermal quenching and show that the luminescence quenching temperature is high, around 460-490 K, which makes these Mn4+-doped hexafluoroaluminates interesting red phosphors for w-LEDs. The new insights reported on the synthesis and optical properties of Mn4+ in the chemically and thermally stable hexafluoroaluminates can contribute to the optimization of red-emitting Mn4+ phosphors for w-LEDs.
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Project description:Red-emitting Mn4+-doped fluorides are a promising class of materials to improve the color rendering and luminous efficacy of white light-emitting diodes (w-LEDs). For w-LEDs, the luminescence quenching temperature is very important, but surprisingly no systematic research has been conducted to understand the mechanism for thermal quenching in Mn4+-doped fluorides. Furthermore, concentration quenching of the Mn4+ luminescence can be an issue but detailed investigations are lacking. In this work, we study thermal quenching and concentration quenching in Mn4+-doped fluorides by measuring luminescence spectra and decay curves of K2TiF6:Mn4+ between 4 and 600 K and for Mn4+ concentrations from 0.01% to 15.7%. Temperature-dependent measurements on K2TiF6:Mn4+ and other Mn4+-doped phosphors show that quenching occurs through thermally activated crossover between the 4T2 excited state and 4A2 ground state. The quenching temperature can be optimized by designing host lattices in which Mn4+ has a high 4T2 state energy. Concentration-dependent studies reveal that concentration quenching effects are limited in K2TiF6:Mn4+ up to 5% Mn4+. This is important, as high Mn4+ concentrations are required for sufficient absorption of blue LED light in the parity-forbidden Mn4+ d-d transitions. At even higher Mn4+ concentrations (>10%), the quantum efficiency decreases, mostly due to direct energy transfer to quenching sites (defects and impurity ions). Optimization of the synthesis to reduce quenchers is crucial for developing more efficient highly absorbing Mn4+ phosphors. The present systematic study provides detailed insights into temperature and concentration quenching of Mn4+ emission and can be used to realize superior narrow-band red Mn4+ phosphors for w-LEDs.
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Project description:The effects of the sintering temperature on microstructures, electrical properties, and dielectric response of 1%Cr3+/Ta5+ co-doped TiO2 (CrTTO) ceramics prepared using a solid-state reaction method were studied. The mean grain size increased with an increasing sintering temperature range of 1300-1500 °C. The dielectric permittivity of CrTTO ceramics sintered at 1300 °C was very low (ε' ∼198). Interestingly, a low loss tangent (tanδ ∼0.03-0.06) and high ε' (∼1.61-1.9 × 104) with a temperature coefficient less than ≤ ±15% in a temperature range of -60 to 150 °C were obtained. The results demonstrated a higher performance property of the acceptor Cr3+/donor Ta5+ co-doped TiO2 ceramics compared to the Ta5+-doped TiO2 and Cr3+-doped TiO2 ceramics. According to a first-principles study, high-performance giant dielectric properties (HPDPs) did not originate from electron-pinned defect dipoles. By impedance spectroscopy (IS), it was suggested that the giant dielectric response was induced by interfacial polarization at the internal interfaces rather than by the formation of complex defect dipoles. X-ray photoelectron spectroscopy (XPS) results confirmed the existence of Ti3+, resulting in the formation of semiconducting parts in the bulk ceramics. Low tanδ and excellent temperature stability were due to the high resistance of the insulating layers with a very high potential barrier of ∼2.0 eV.
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Project description:Red phosphor plays a crucial role in improving the quality of white light illumination and backlight displays. However, significant challenges remain to enhance red emission intensity in different matrix materials. Herein, a class of two-phase mixing red phosphors of NaIn1-x(MoO4)2:xEu3+ (NIMO:xEu3+) has been successfully prepared by the traditional high-temperature solid-state reaction method. The coordination environment, phase structure, excitation and emission spectra, fluorescence kinetics, and temperature-dependent luminescence properties of the system have been studied comprehensively. It is worth mentioning that the red emission intensity continues to increase with the increased Eu3+ doping concentration, and the fluorescence lifetimes remain unchanged. These extraordinary phenomena mainly stem from the special concentration quenching mechanism in such two-phase mixing material, namely, the increased lattice interface barriers from Eu six-coordinated units and Eu eight-coordinated units can effectively block the non-radiation by enlarging the average distance between luminescent centers. The improved fluorescence thermal stability and suppressed non-radiative transition rate in NIMO:40%Eu3+ sample are further proving regulatory role of lattice interface barriers. In addition, a warm white light-emitting diode (LED) is successfully fabricated, exhibiting Commission Internationale de l'Eclairage (CIE) coordinates of (0.343, 0.335), a color rendering index (CRI) of 92.1, and a correlated color temperature (CCT) of 5013 K, showing significant application prospects for high-quality lighting devices.
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Project description:Emerging phototherapy in a clinic and plant photomorphogenesis call for efficient red/far-red light resources to target and/or actuate the interaction of light and living organisms. Rare-earth-doped phosphors are generally promising candidates for efficient light-emitting diodes but still bear lower quantum yield for the far-red components, potential supply risks, and high-cost issues. Thus, the design and preparation of efficient non-rare-earth activated phosphors becomes extremely important and arouses great interest. Fabrication of Cr3+-doped Na3AlF6 phosphors significantly promotes the potential applications by efficiently converting blue excitation light of a commercial InGaN chip to far-red broadband emission in the 640-850 nm region. The action response of phototherapy (∼667-683 nm; ∼750-772 nm) and that of photomorphogenesis (∼700-760 nm) are well overlapped. Based on the temperature-dependent steady luminescence and time-resolved spectroscopies, energy transfer models are rationally established by means of the configurational coordinate diagram of Cr3+ ions. An optimal sample of Na3AlF6:60% Cr3+ phosphor generates a notable QY of 75 ± 5%. Additionally, an InGaN LED device encapsulated by using Na3AlF6:60% Cr3+ phosphor was fabricated. The current exploration will pave a promising way to engineer non-rare-earth activated optoelectronic devices for all kinds of photobiological applications.
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Project description:This article contains data of time of flight secondary ion mass spectrometry (TOF-SIMS) analysis of brushite-forming calcium phosphate cements doped with biologically active metal ions. This data are related to the research article "Cu2+, Co2+ and Cr3+ doping of a calcium phosphate cement influences materials properties and response of human mesenchymal stromal cells" (Schamel et al., 2017) [1]. Cu2+, Co2+ and Cr3+ doped ?-tricalcium phosphate precursor powders were used to prepare cement samples. The incorporation and distribution of the metal ions in the cement matrix was visualized by imaging mass spectrometry.
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