Search Results (17)

Composite phosphor ceramics for warm white LED lighting were fabricated with K₂SiF₆:Mn⁴⁺ (KSF) as both a narrowband red phosphor and a translucent matrix in which yellow-emitting Y₃Al₅O₁₂:Ce³⁺ (YAG) particles were dispersed. The emission spectra of these composites under blue LED excitation were studied as a function of YAG loading and thickness. Warm white light with a color temperature of 2716 K, a high CRI of 92.6, and an R9 of 77.6 was achieved. A modest improvement in the thermal conductivity of the KSF ceramic of up to 9% was observed with the addition of YAG particles. In addition, a simple model was developed for predicting the emission spectra based on several parameters of the composite ceramics and validated with the experimental results. The emission spectrum can be tuned by varying the dopant concentrations, thickness, YAG loading, and YAG particle size. This work demonstrates the utility of KSF/YAG composite phosphor ceramics as a means of producing warm white light, which are potentially suitable for higher-drive applications due to their increased thermal conductivity and reduced droop compared with silicone-dispersed phosphor powders. Full article

Mn⁴⁺-doped red-light-emitting phosphors have become a research hotspot that can effectively enhance photosynthesis and promote morphogenesis in plants. Herein, the red phosphor La₃Mg₂NbO₉:Mn⁴⁺ was synthesized through the solid-state reaction method. The effects of adding H₃BO₃ and a charge compensator R⁺ (R = Li, Na, K) on the crystal structure, morphology, quantum efficiency, and luminous performance of the La₃Mg₂NbO₉:Mn⁴⁺ phosphor were systematically analyzed, respectively. The results showed that adding H₃BO₃ flux and a charge compensator improved the quantum efficiency and luminescence intensity. The emission intensity of the phosphor was enhanced about 5.9 times when Li⁺ was used as the charge compensator, while it was enhanced about 240% with the addition of H₃BO₃ flux. Remarkably, it was also found that the addition of H₃BO₃ flux and a charge compensator simultaneously improved the thermal stability at 423 K from 47.3% to 68.9%. The prototype red LED fabricated using the La₃Mg₂NbO₉:Mn⁴⁺,H₃BO₃,Li⁺ phosphor exhibited a perfect overlap with the phytochrome absorption band for plant growth. All of these results indicate that the La₃Mg₂NbO₉:Mn⁴⁺,H₃BO₃,Li⁺ phosphor has great potential for use in agricultural plant lighting. Full article

Fabricating far-red light-emitting diodes (LEDs) with high emission efficiency is a change for the application in plant growth. In this work, a new type of far-red LED was fabricated for plant growth by encapsulating the Sr₃LiSbO₆:Mn⁴⁺, Mg²⁺ (SLSO:Mn⁴⁺, Mg²⁺) far-red phosphors with the gradient-refractive glass films. Under 365 nm excitation, the phosphors emitted the wide band in the 550–800 nm range, which overlapped with the absorption band of plants that absorb far-red light (PFR). The internal quantum efficiency (IQE) of the LED was 93.6%. Compared with the luminous efficacy of traditional (fluorescent silicone) LEDs (59 lm/W), the luminous efficacy of the new LED is increased by 62.7%, and reaches 96.74 lm/W. Thus, this far-red LED with high IQE has a long-term application prospect in plant growth. Full article

All-inorganic perovskite nanocrystals (NCs) have attractive potential for applications in display and lighting fields due to their special optoelectronic properties. However, they still suffer from poor water and thermal stability. In this work, green CsPbBr₃-alginic acid (CsPbBr₃-AA) perovskite composites were synthesized by an in situ hot-injection process which showed a high photoluminescence quantum yield (PLQY) of 86.43% and improved moisture and thermal stability. Finally, white light-emitting diodes (WLEDs) were fabricated by combining the green CsPbBr₃-AA perovskite composites with red K₂SiF₆:Mn⁴⁺ phosphors and blue InGaN LED chips. The WLEDs show a relatively high luminous efficacy of 36.4 lm/W and a wide color gamut (124% of the National Television System Committee). These results indicate that the green CsPbBr₃-AA perovskite composites have great potential applications in backlight displays. Full article

Nowadays, Mn⁴⁺-activated fluoride red phosphors with excellent luminescence properties have triggered tremendous attentions for enhancing the performance of white light-emitting diodes (WLEDs). Nonetheless, the poor moisture resistance of these phosphors impedes their commercialization. Herein, we proposed the dual strategies of “solid solution design” and “charge compensation” to design K₂Nb_1−xMo_xF₇ novel fluoride solid solution system, and synthesized the Mn⁴⁺-activated K₂Nb_1−xMo_xF₇ (0 ≤ x ≤ 0.15, x represents the mol % of Mo⁶⁺ in the initial solution) red phosphors via co-precipitation method. The doping of Mo⁶⁺ not only significantly improve the moisture resistance of the K₂NbF₇: Mn⁴⁺ phosphor without any passivation and surface coating, but also effectively enhance the luminescence properties and thermal stability. In particular, the obtained K₂Nb_1−xMo_xF₇: Mn⁴⁺ (x = 0.05) phosphor possesses the quantum yield of 47.22% and retains 69.95% of its initial emission intensity at 353 K. Notably, the normalized intensity of the red emission peak (627 nm) for the K₂Nb_1−xMo_xF₇: Mn⁴⁺ (x = 0.05) phosphor is 86.37% of its initial intensity after immersion for 1440 min, prominently higher than that of the K₂NbF₇: Mn⁴⁺ phosphor. Moreover, a high-performance WLED with high CRI of 88 and low CCT of 3979 K is fabricated by combining blue chip (InGaN), yellow phosphor (Y₃Al₅O₁₂: Ce³⁺) and the K₂Nb_1−xMo_xF₇: Mn⁴⁺ (x = 0.05) red phosphor. Our findings convincingly demonstrate that the K₂Nb_1−xMo_xF₇: Mn⁴⁺ phosphors have a good practical application in WLEDs. Full article

Far-red (FR) emitting LEDs are known as a promising supplement light source for photo-morphogenesis of plants, in which FR emitting phosphors are indispensable components. However, mostly reported FR emitting phosphors are suffering from problems of wavelength mismatch with LED chips or low quantum efficiency, which are still far from practical applications. Here, a new efficient FR emitting double-perovskite phosphor BaLaMgTaO₆:Mn⁴⁺ (BLMT:Mn⁴⁺) has been prepared by sol-gel method. The crystal structure, morphology and photoluminescence properties have been investigated in detail. BLMT:Mn⁴⁺ phosphor has two strong and wide excitation bands in the range of 250–600 nm, which matches well with a near-UV or blue chip. Under 365 nm or 460 nm excitation, BLMT:Mn⁴⁺ emits an intense FR light ranging from 650 to 780 nm with maximum emission at 704 nm due to ²E_g → ⁴A_2g forbidden transition of Mn⁴⁺ ion. The critical quenching concentration of Mn⁴⁺ in BLMT is 0.6 mol%, and its corresponding internal quantum efficiency is as high as 61%. Moreover, BLMT:Mn⁴⁺ phosphor has good thermal stability, with emission intensity at 423 K keeping 40% of the room temperature value. The LED devices fabricated with BLMT:Mn⁴⁺ sample exhibit bright FR emission, which greatly overlaps with the absorption curve of FR absorbing phytochrome, indicating that BLMT:Mn⁴⁺ is a promising FR emitting phosphor for plant growth LEDs. Full article

White light emitting diodes (WLEDs) are widely used due to their advantages of high efficiency, low electricity consumption, long service life, quick response time, environmental protection, and so on. The addition of red phosphor is beneficial to further improve the quality of WLEDs. The search for novel red phosphors has focused mainly on Eu²⁺ ion- and Mn⁴⁺ ion-doped compounds. Both of them have emissions in the red region, absorption in blue region, and similar quantum yields. Eu²⁺-doped phosphors possess a rather broad-band emission with a tail in the deep red spectral range, where the sensitivity of the human eye is significantly reduced, resulting in a decrease in luminous efficacy of WLEDs. Mn⁴⁺ ions provide a narrow emission band ~670 nm in oxide hosts, which is still almost unrecognizable to the human eye. Mn⁴⁺-doped fluoride phosphors have become one of the research hotspots in recent years due to their excellent fluorescent properties, thermal stability, and low cost. They possess broad absorption in the blue region, and a series of narrow red emission bands at around 630 nm, which are suitable to serve as red emitting components of WLEDs. However, the problem of easy hydrolysis in humid environments limits their application. Recent studies have shown that constructing a core–shell structure can effectively improve the water resistance of Mn⁴⁺-doped fluorides. This paper outlines the research progress of Mn⁴⁺-doped fluoride A₂MF₆ (A = Li, Na, K, Cs, or Rb; M = Si, Ti, Ge or Sn), which has been based on the core–shell structure in recent years. From the viewpoint of the core–shell structure, this paper mainly emphasizes the shell layer classification, synthesis methods, luminescent mechanism, the effect on luminescent properties, and water resistance, and it also gives some applications in terms of WLEDs. Moreover, it proposes challenges and developments in the future. Full article

The anti-counterfeiting technology of banknotes, bills and negotiable securities is constantly copied, and it is urgent to upgrade its anti-counterfeiting technology. In view of the defect of easy replication of single-wavelength anti-counterfeiting technology, the bonded copolymer PMEuTb was synthesized, employing the technique of first coordination and then polymerization. The molecular structure of copolymer PMEuTb was confirmed by infrared spectrum and UV-vis absorption spectrum. The internal mechanism of negative correlation between initiator concentration and number-average molecular weight M_n of the copolymer was revealed, and the positive correlation between M_n and luminescent behavior of the copolymer was analyzed. The luminescent properties of copolymer PMEuTb with initiator amount of 0.1% were investigated, the copolymer PMEuTb exhibits dual-wavelength emission of green light and red light under the excitation of ultraviolet light at 254 nm and 365 nm. The copolymer has the lifetime of 1.083 ms at ⁵D₄–⁷F₅ transition and 0.665 ms at ⁵D₀–⁷F₂ transition, which belongs to phosphorescent emitting materials. The copolymer remains stable at 240 °C, and variable temperature photoluminescent spectra demonstrate the luminescent intensity remains 85% at 333 K, meeting the requirements of room temperature phosphorescent anti-counterfeiting materials. The luminescent patterns made by standard screen printing display the green and cuticolor logo at 254 nm and 365 nm, respectively, indicating that the bonded phosphors PMEuTb has potential application in phosphorescent anti-counterfeiting. Full article

Non-rare earth doped oxide phosphors with far-red emission have become one of the hot spots of current research due to their low price and excellent physicochemical stability as the red component in white light-emitting diodes (W-LEDs) and plant growth. Herein, we report novel Mn⁴⁺-doped La₂CaSnO₆ and La₂MgSnO₆ phosphors by high-temperature solid-phase synthesis and analyzed their crystal structures by XRD and Rietveld refinement. Their excitation spectra consist of two distinct excitation bands with the dominant excitation range from 250 to 450 nm, indicating that they possess strong absorption of near-ultraviolet light. Their emission is located around 693 and 708 nm, respectively, and can be absorbed by the photosensitive pigments Pr and Pfr, proving their great potential for plant growth. Finally, the prepared samples were coated with 365 nm UV chips to fabricate far-red LEDs and W-LEDs with low correlation color temperature (CCT = 4958 K/5275 K) and high color rendering index (R_a = 96.4/96.6). Our results indicate that La₂CaSnO₆:Mn⁴⁺ and La₂MgSnO₆:Mn⁴⁺ red phosphors could be used as candidate materials for W-LED lighting and plant growth. Full article

In this work, a novel red-emitting oxyfluoride phosphor Na₂NbOF₅:Mn⁴⁺ with an ultra-intense zero-phonon line (ZPL) was successfully synthesized by hydrothermal method. The phase composition and luminescent properties of Na₂NbOF₅:Mn⁴⁺ were studied in detail. The photoluminescence excitation spectrum contains two intense excitation bands centered at 369 and 470 nm, which match well with commercial UV and blue light-emitting diode (LED) chips. When excited by 470 nm blue light, Na₂NbOF₅:Mn⁴⁺ exhibits red light emission dominated by ZPL. Notably, the color purity of the Na₂NbOF₅:Mn⁴⁺ red phosphor can reach 99.9%. Meanwhile, the Na₂NbOF₅:Mn⁴⁺ phosphor has a shorter fluorescence decay time than commercial K₂SiF₆:Mn⁴⁺, which is conducive to fast switching of images in display applications. Profiting from the intense ZPL, white light-emitting diode (WLED) with high color rendering index of Ra = 86.2 and low correlated color temperature of T_c = 3133 K is realized using yellow YAG:Ce³⁺ and red Na₂NbOF₅:Mn⁴⁺ phosphor. The WLED fabricated using CsPbBr₃ quantum dots (QDs) and red Na₂NbOF₅:Mn⁴⁺ phosphor shows a wide color gamut of 127.56% NTSC (National Television Standard Committee). The results show that red-emitting Na₂NbOF₅:Mn⁴⁺ phosphor has potential application prospects in WLED lighting and display backlight. Full article

A two-dimensional nanostructured fluoride red-emitting phosphor with an excellent quantum yield of ~91% is studied for cost-effective and high-color quality nanowire white light-emitting diodes (WLEDs). K₂TiF₆:Mn⁴⁺ phosphors are synthesized via an emulsification method using surfactants as sodium dodecyl sulphonate and oleic acid. The K₂TiF₆:Mn⁴⁺ phosphors in ultra-thin and nanosheet crystals are observed via scanning electron microscopy and high-resolution transmission electron microscopy. The surfactants are found to play a key role in inhibition of KTFM crystal growth process and stabilization of Mn⁴⁺ ions doping into the K₂TiF₆ host. The prepared phosphors exhibited intensive red emission at approximately 632 nm and excellent thermal stability in the range of 300–500 K upon 460 nm light excitation. Moreover, the K₂TiF₆:Mn⁴⁺ nanosheets were integrated on InGaN/AlGaN nanowire WLEDs for color quality study. The results show that the nanowire WLEDs with red-emitting phosphor exhibit unprecedentedly high color rendering index ~96.4, and correlated color temperature ~4450 K. Full article

Samples of magnesium aluminum spinel ceramics doped with manganese ions were prepared by a high-temperature solid-state reaction method; their potential as red-emitting phosphors was analyzed using a time-resolved luminescence spectroscopy technique, from room temperature to 10 K. It was found that in the red spectral range, the luminescence spectra of manganese ions in the MgAl₂O₄ spinel showed a narrow band peaking at 651 nm due to the emission of Mn⁴⁺ and a broader emission band in the region of 675 ÷ 720 nm; the ratio of intensities for these bands depends on the synthesis conditions. By applying a special multi-step annealing procedure, the MgAl₂O₄:Mn⁴⁺ phosphor containing only tetravalent manganese ions, Mn⁴⁺, was synthesized. Broad-band far-red emission observed from MgAl₂O₄:Mn and Mg_1.25Al_1.75O_3.75F_0.25:Mn phosphors, prepared by a conventional method of a solid-state reaction, was interpreted as coming from Mn³⁺ ions. Full article

Mn⁴⁺ activated LaMgAl₁₁O₁₉ (LMA/Mn⁴⁺) with red emitting phosphor was obtained by sintering under air conditioning. The X-ray diffraction pattern Rietveld refinement results reveal that three six-fold coordinated Al sites are substituted by Mn⁴⁺ ions. Furthermore, the chemical valence state of manganese in the LMA host was further confirmed through X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). Photoluminescence emission (PL) and excitation (PLE) spectra of LMA/Mn⁴⁺ as well as the lifetime were measured, and the 663 nm emission is ascribed to the ²E_g→⁴A_2g from the 3d³ electrons in the [MnO₆]⁸⁻ octahedral complex. The emission spectrum matches well with the absorption of phytochrome. Temperature-dependent PL spectra show that the color changes of the phosphor at 420 K are 0.0110 for Δx and −0.0109 for Δy. Moreover, doping Zn²⁺ and Mg²⁺ ions in the host enhances the emission intensity of Mn⁴⁺ ions. These results highlight the potential of LMA/Mn⁴⁺ phosphor for a light-emitting diode (LED) plant lamp. Full article

Phosphors based on magnesium titanate activated with Mn ${}^{4+}$ ions are of great interest because, when excited with blue light, they display a strong red-emitting luminescence. They are characterized by a luminescence decay which is strongly temperature dependent in the range from −50 ${}^{\circ }$ C to 150 ${}^{\circ }$ C, making these materials very promising for temperature sensing in the biochemical field. In this work, the optical and thermal properties of the luminescence of Mg ${}_2$ TiO ${}_4$ are investigated for different Mn ${}^{4+}$ doping concentrations. The potential of this material for temperature sensing is demonstrated by fabricating a fiber optic temperature microsensor and by comparing its performance against a standard resistance thermometer. The response of the fiber optic sensor is exceptionally fast, with a response time below 1 s in the liquid phase and below 1.1 s in the gas phase. Full article

Mn⁴⁺-activated phosphors are emerging as a novel class of deep red/near-infrared emitting persistent luminescence materials for medical imaging as a promising alternative to Cr³⁺-doped nanomaterials. Currently, it remains a challenge to improve the afterglow and photoluminescence properties of these phosphors through a traditional high-temperature solid-state reaction method in air. Herein we propose a charge compensation strategy for enhancing the photoluminescence and afterglow performance of Mn⁴⁺-activated LaAlO₃ phosphors. LaAlO₃:Mn⁴⁺ (LAO:Mn⁴⁺) was synthesized by high-temperature solid-state reaction in air. The charge compensation strategies for LaAlO₃:Mn⁴⁺ phosphors were systematically discussed. Interestingly, Cl⁻/Na⁺/Ca²⁺/Sr²⁺/Ba²⁺/Ge⁴⁺ co-dopants were all found to be beneficial for enhancing LaAlO₃:Mn⁴⁺ luminescence and afterglow intensity. This strategy shows great promise and opens up new avenues for the exploration of more promising near-infrared emitting long persistent phosphors for medical imaging. Full article