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Preparation of CdTe superparticles for white light-emitting diodes without F?rster resonance energy transfer
摘要： Due to many unique and excellent optical properties, quantum dots (QDs) have been seen as one of the most promising color conversion materials in light-emitting diodes (LEDs). However, the F¨orster resonance energy transfer (FRET) among di?erent colored QDs always causes a signi?cant red-shift of the ?uorescence emission, impeding the fabrication of LEDs with predicted photoluminescence (PL) emission spectra. In this work, we take advantage of CdTe superparticles (SPs), which are assembled by CdTe QDs, as the color conversion materials for the fabrication of WLEDs. Because of their submicron size, the distance between QDs with di?erent emissions can be large enough to avoid the FRET process. More importantly, this method provides us with an opportunity to precisely design and regulate the PL emission spectra of LEDs. By easily overlapping the individual PL spectra of CdTe SPs with di?erent emissions, the certain ratio of their usage for fabricating LEDs with desired PL emission spectra is identi?ed. According to this idea, a WLED with a color rendering index (CRI) of 81, luminous e?cacy of 27 lm W(cid:1)1, and color coordinate at (0.33, 0.34) with the color temperature of 5742 K is achieved.
关键词： F¨orster resonance energy transfer,white light-emitting diodes,quantum dots,color conversion materials,CdTe superparticles
更新于2025-09-16 10:30:52
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A simple and green synthesis of carbon quantum dots from coke for white light-emitting devices
摘要： Coke is a by-product of coal. This paper reports a simple and green chemical oxidation method for carbon quantum dots (CQDs) from coke for use in novel applications. The CQDs emit blue fluorescence and have a fluorescence quantum yield of 9.2% and blue-green-red spectral composition of 48%. A light-emitting diode (LED) was fabricated by combining the CQDs as a white-light converter with an ultraviolet chip. The Commission Internationale de L'Eclairage chromaticity coordinate (0.31, 0.35) and correlated color temperature (5125 K) of the LED are located in a cool white light zone, suggesting that they have superior potential application in lighting devices.
关键词： carbon quantum dots,white light-emitting devices,fluorescence,coke,chemical oxidation
更新于2025-09-16 10:30:52
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Bright emission and high photoluminescence CsPb <sub/>2</sub> Br <sub/>5</sub> NCs encapsulated in mesoporous silica with ultrahigh stability and excellent optical properties for white light-emitting diodes
摘要： All-inorganic cesium lead halide perovskite CsPb2Br5 nanocrystals (NCs) have attracted tremendous attention owing to their unique optoelectronic properties. However, their tolerance to atmospheric moisture is limited by their corresponding poor stability, which has drastically prevented the broad application of the materials in lasers, light-emitting diodes (LED) and, most recently, photocatalysis. To address this issue, we have successfully demonstrated the design and synthesis of a nanocomposite material, CsPb2Br5 NCs coated in mesoporous silica (NCs-MS), with high photoluminescence (PL) intensity, bright emission and enhanced water stability, thermal stability and photostability versus naked CsPb2Br5 NCs. The components and structure of the prepared CsPb2Br5 NCs-MS nanocomposite were investigated in detail by PL, XRD, TEM and HAADF-STEM studies. Furthermore, the mechanism behind the outstanding stability and optical properties of the prepared NCs-MS nanocomposite is discussed. Owing to the ultrahigh stability of the NCs-MS nanocomposite, the white LED (WLED) assembled by coating the CsPb2Br5 NCs-MS nanocomposite and commercial red CaAlSiN3:Eu2+ phosphor powder on an InGaN blue chip showed CIE chromaticity coordinates of (0.3377, 0.3309) and presented excellent optical parameters with a CRI of 82.9, a CCT of 5035 K and an LE of 64.9 lm W?1. This work provides a new pathway for the synthesis and application of all-inorganic cesium lead halide perovskite materials in WLEDs and display devices.
关键词： stability,white light-emitting diodes,mesoporous silica,photoluminescence,CsPb2Br5 NCs
更新于2025-09-16 10:30:52
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Efficient blue-white color luminescence with near-ultraviolet excitation in Dy3+/Tm3+:Na3Gd(PO4)2 nanophosphor for white LEDs
摘要： The Dy3t/Tm3t ions co-activated Na3Gd(PO4)2 phosphors were synthesized by the citrate-gel based combustion technique. The structural properties of as-synthesized phosphors were studied through X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The influence of Tm3t concentration on the fluorescence properties of Na3Gd(PO4)2:Dy3t phosphors were systematically investigated under near-UV light irradiation of 359 and 352 nm. The energy transfer efficiency (ηET) of as-prepared phosphors increases gradually from 17 to 42%, and the critical distance (Rc) between Dy3t and Tm3t ions is calculated to be 4.76 ?. For better understanding the energy transfer mechanism (ET:Dy3t →Tm3t), the decay curves were utilized on the basis of Dexter’s energy transfer formula and Reisfeld’s approximation. More importantly, the obtained CIE color coordinates of Na3Gd(PO4)2:Dy3t/Tm3t phosphors located at blue-white region under near-UV light irradiation. The results demonstrate the promising application of Na3Gd(PO4)2:Dy3t/Tm3t phosphor for near-UV white LEDs.
关键词： Citrate-gel combustion technique,Decay times-Energy transfer mechanism,Photoluminescence,White-light,Dy3t/Tm3t
更新于2025-09-16 10:30:52
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A novel multi-center activated single-component white light-emitting phosphor for deep UV chip-based high color-rendering WLEDs
摘要： Single-component white light-emitting phosphors for phosphors-converted WLEDs are a hot spot of solid-state lighting field. Dy3+ is a promising candidate for white light generation in single-component hosts; however, the inappropriate ratio of yellow light to blue and the lack of red light restrict its applications in full-color display and indoor lighting. Here, a novel multi-center activated single-component white light-emitting phosphor, Sr2LaGaO5:Dy3+,Sm3+, has been designed and synthesized. It is surprisingly found that there is no evident energy transfer between the host and the dopants even though they satisfy the rule of spectral overlap, which can be explained from the special structure of the phosphor. The co-excitation of the host and the dopants would be a facile strategy to finely tune the luminescent spectra of phosphors. By adjusting the doping concentrations of Dy3+ and Sm3+, we can control the relative intensities of the emissions peaked at 493 nm and 574 nm from Dy3+, 604 nm from Sm3+ and the broadband within the range of 400 - 500 nm from the host. Therefore, the emission color of the co-doped phosphors can be tuned from white light to orangish red region with correlated color temperature decreasing from 5708 K to 1971 K. A WLED device with extremely high color-rendering index (Ra) up to 91.4 was fabricated by coating the synthesized phosphor with a deep UV LED chip. And it is the first time to use a single-component white light-emitting phosphor co-activated with Dy3+ and Sm3+ in deep UV chip excited WLEDs with high Ra.
关键词： Co-excitation,Sr2LaGaO5:Dy3+,Sm3+,Deep UV-LED chip,White light-emitting phosphor,High color-rendering index
更新于2025-09-16 10:30:52
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White-light/tunable emissions in single-phased BaLa2Si3O10:Eu3+, Bi3+ phosphor for the simultaneous applications in white light-emitting diodes and luminous cement
摘要： In this work, we report the single-phased BaLa2Si3O10:Eu3+, Bi3+ phosphor with white-light/tunable emissions under UV excitations. We find the emissions of Bi3+-doped BaLa2Si3O10 samples are dependent on the excitation spectral wavelength, where exciting by the wavelength from 240 to 410 nm range can lead to the tunable Bi3+ emissions owing to the intensity change of three emission bands (i.e., 367 nm, 423 nm, and 516 nm). After co-doping the Eu3+ ions into Bi3+-doped BaLa2Si3O10, the energy transfer from Bi3+ to Eu3+ ions dominated by a dipole–quadrupole (d–q) interaction mechanism is proved. Typically, by exciting with 365 nm and varying the Eu3+ content, the tunable emissions from blue, white to red are observable in the BaLa2Si3O10:Eu3+, Bi3+. By coating the white BaLa2Si3O10:Eu3+, Bi3+ sample with a commercial 365-nm UV LED chip or mixing it with the cement, we not only achieve the white-light LEDs device with the desirable color rendering index (CRI) of 95, excellent luminescent efficiency of 80 lm/W, and good excellent color temperature (CT) of 4215 K at the CIE chromaticity of (0.338, 0.357), but also achieve the luminous cement.
关键词： white light-emitting diodes,single-phased phosphor,white-light/tunable emissions,luminous cement,BaLa2Si3O10:Eu3+,Bi3+
更新于2025-09-12 10:27:22
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High perovskite-to-manganese energy transfer efficiency in single-component white-emitting Mn-doped halide perovskite quantum dots
摘要： Taking advantages of negligible reabsorption and no phase separation, single-component white-emitting phosphors are believed as new promising color conversion materials for white light-emitting diodes. As a potential candidate, Mn-doped lead halide perovskites are studied intensively, but rare works can realize pure white emission with a single component due to the challenge for realizing sufficient energy transfer efficiency from perovskite to Mn at the desirable emission wavelengths. In this work, we reported the synthesis of single-component white light halide perovskite quantum dots (QDs) by doping Mn into the host of CsPb(Cl/Br)3@CsPb(Cl/Br)x core–amorphous shell (CAS). The small size of zero-dimensional core in CAS structure has a strong quantum confinement effect, which can enhance the energy transfer efficiency from halide perovskite to Mn impurity dramatically. Our result shows 19.3 times higher energy transfer efficiency for Mn-doped CAS than that of ordinary Mn-doped CsPb(Cl/Br)3 nanocubes. As a result, as-prepared Mn-doped CAS QDs give rise to a white light emission with Commission Internationale de l’Eclairage (CIE) color coordinates of (0.37, 0.33). After blending with polystyrene (PS), Mn-doped CAS QDs can be used as a single-component color conversion material for assembling white light LEDs.
关键词： energy transfer efficiency,white-emitting phosphors,white light LEDs,Mn-doped lead halide perovskites,quantum dots
更新于2025-09-12 10:27:22
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Investigation of LED Non-linearity on DCO-OFDM and ACO-OFDM in VLC Systems using Multichip RGB LEDs for Indoor Applications
摘要： The impact of the LED non-linearity on the Intensity Modulation Direct Detection (IM-DD) in the VLC using OFDM for white light generated using RGB LEDs for indoor applications is analyzed. This work extends the orders of harmonics for analysis and investigates the impact of this non-linearity issue on OFDM techniques. The wavelengths (Red, Green and Blue) are individually set at the LED and their induced photocurrent in a Si PD is calculated. The result shows that the wavelength corresponding to the 625nm induces 5dB and 3dB more power than 528nm and 458nm respectively. We choose 625nm as the OFDM signal carrier for transmission keeping the other two un-modulated. We compare the effects of the non-linearity of the LED on the two OFDM techniques- Asymmetrical clipped optical (ACO) and Direct current biased optical (DCO). Our simulation results show that the power of the 2nd and 3rd order intermodulation components for ACO-OFDM is 3dB lesser than DCO-OFDM. The required SNR for ACO-OFDM is found to be 3dB lesser as compared to DCO-OFDM. The clipping effect of the LED remains unchanged irrespective of the OFDM variation applied.
关键词： Visible Light Communication,White Light,ACO-OFDM,LED,DCO-OFDM,Non-Linear Distortion
更新于2025-09-12 10:27:22
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Carbon Dots exhibiting Concentration-Dependent Full-Visible-Spectrum Emission for Light-Emitting Diode Applications
摘要： Carbon dots (CDs) that exhibit emission over the whole visible spectrum are desired for using in light-emitting diodes. Here, CDs displaying tunable fluorescence over the whole visible region are synthesized. Different concentrations of CDs are uniformly dispersed in epoxy resin and coated on 405-nm LED chips to obtain monochrome blue, cyan, green, yellow, red, and deep red LEDs that yield a color gamut covering 99.4% of the National Television Standards Committee (NTSC) standard. These monochrome LEDs display similar stability decay curves. Furthermore, warm and neutral white LEDs are produced by coating cyan- and red-emitting CD layers on 405-nm LED chips, achieving color rendering indexes (CRI) of 96.4 and 96.6, respectively. Two fluorescent conversion layers derived from one material at different concentrations simplifies the preparation of high-CRI white LEDs. The uniform weak changes of the cyan and red PL peaks during operation ensures the high stability of these CD-based white LEDs. This research provides a new avenue to develop low-cost, easy-to-prepare CDs with tunable emission colors as alternative phosphors for LED-based high-performance displays and lighting.
关键词： full-visible-spectrum emission,monochrome light-emitting diodes,concentration-dependent spectrum-tunable carbon dots,high color rendering index,white-light-emitting diodes
更新于2025-09-12 10:27:22
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White Light-Emitting Diodes With Ultrahigh Color Rendering Index by Red/Green Phosphor Layer Configuration Structure
摘要： Currently, white light-emitting diodes (WLEDs) have been widely applied in lighting, display, and medical fields. However, there still exists the problem of low color rendering index (CRI, Ra). In this work, phosphor-converted WLEDs (pc-WLEDs) with ultrahigh Ra were fabricated using Y3Al3Ga2O12:Ce3+ green phosphor and CaAlSiN3:Eu2+ red phosphor configuration structure. The broad emission spectrum of the green phosphor compensates for the gap of the cyan-emitting region that realizes full-spectrum white-light emission. The weight ratio of green/red phosphors was controlled to optimize the optical performances of pc-WLEDs. At the ratio of 0.15/0.012, the fabricated pc-WLED exhibits a natural white light with an ultrahigh Ra of 95.2 and an incredibly small International Commission on Illumination (CIE) chromaticity coordinates deviation (Duv = ?0.0034) at 350 mA. The corresponding correlated color temperature (CCT) and luminous efficiency (LE) are 4526 K and 62.34 lm/W, respectively. Furthermore, two separated phosphor configuration structures were constructed for pc-WLEDs. The R up/G down structure achieves the highest LE of 64.93 lm/W, and the corresponding CCT and Ra are 5714 K and 95.8, respectively, chiefly due to the compensation for reabsorption effect caused by the large difference in the luminous efficacy of radiation (LER) between dichromatic phosphors. The results demonstrate that by adjusting the phosphor configuration structure, the pc-WLEDs with high color rendering can be obtained, which have great applications in high-quality lighting.
关键词： white light-emitting diodes (WLEDs),High color rendering,separated phosphor layer,phosphor configuration
更新于2025-09-12 10:27:22