Blue Light-emitting Diode Chip Research Articles

Organic fluorescent dyes supported on activated boron nitride: a promising blue light excited phosphors for high-performance white light-emitting diodes.

We report an effective and rare-earth free light conversion material synthesized via a facile fabrication route, in which organic fluorescent dyes, i.e. Rhodamine B (RhB) and fluorescein isothiocyanate (FITC) are embedded into activated boron nitride (αBN) to form a composite phosphor. The composite phosphor shows highly efficient Förster resonance energy transfer and greatly improved thermal stability, and can emit at broad visible wavelengths of 500–650 nm under the 466 nm blue-light excitation. By packaging of the composite phosphors and a blue light-emitting diode (LED) chip with transparent epoxy resin, white LED with excellent thermal conductivity, current stability and optical performance can be realized, i.e. a thermal conductivity of 0.36 W/mk, a Commission Internationale de 1'Eclairage color coordinates of (0.32, 0.34), and a luminous efficiency of 21.6 lm·W−1. Our research opens the door toward to the practical long-life organic fluorescent dyes-based white LEDs.

Flexible quantum dot–PVA composites for white LEDs

Integration of blue light-emitting diode (LED) chips with yellow phosphors has been the most practical way to achieve white lighting, but finding a low-cost alternative for Y3Al5O12:Ce3+ (YAG:Ce) phosphors, which are expensive and lack red emission, is still a great challenge.

Light extraction improvement of blue light-emitting diodes with a Metal-distributed Bragg reflector current blocking layer

The p-electrode of blue light-emitting diodes (LED) chips has a low transmittance on the blue light spectrum. The blue light emitted from the quantum wells under the p-electrode will be severely absorbed by p-electrode, which cause a decrease in blue light extraction efficiency (LEE). In this study, we first designed a current blocking layer (CBL) structure with the blue light reflection through the simulation software. The simulation results show that this structure can effectively improve blue LEE, and then, this structure was verified by experiment. Electroluminescence measurement results show that LED with Metal-distributed Bragg reflector (M-DBR) CBL exhibited better optical performance than the LED with SiO2 CBL and DBR CBL. It was found that M-DBR CBL can effectively increase the blue light reflectivity and prevent the light absorption from the metal p-electrode to improve LED’ blue LEE.

Photoluminescent and thermal properties of (Sr0.995−x−y−zCaxBayMgz)2SiO4:0.01Eu2+ phosphors for warm white light-emitting diodes

A series of phosphors (Sr0.995−x−y−zCaxBayMgz)2SiO4:0.01Eu2+ (0≤x≤0.45, 0≤y≤0.015, 0≤z≤0.35) were synthesized by solid state reaction. Their phase compositions and photoluminescent properties were investigated in detail. The X-ray diffraction analysis indicates the impurity phase of SrSiO3 is formed only when z≥0.25. A photoluminescence investigation shows, with x increasing the emission spectra of the phosphors (0≤x≤0.45, 0≤y≤0.015, z=0) obviously red-shift, the corresponding color tones shift from yellow to orange–yellow and their CCTs reduce from 2875 to 2237K. All the results are beneficial for the phosphors to combining blue light-emitting diode chips to generate warm white light. Besides, the thermal stability of the phosphor (x=0.36, y=z=0) is enhanced by doping Ba2+, due to the greater activation energy for the compounds containing barium.

The photoluminescence and electrical properties of lead-free (Bi0.5Na0.5)TiO3:Pr ceramics

Pr doped lead-free (Bi0.5Na0.5)TiO3(BNT) ceramics were fabricated using the solid-state reaction method. The dependences of photoluminescence properties on process conditions, dopant concentration, and charge compensation were systematically investigated. The results showed that Pr-doped BNT ceramics exhibited strong red emitting properties with a single peak centered at 610nm upon blue light excitation (440–505nm), while maintaining high piezoelectric properties. The emission intensities reached the optimal value as the holding time is 2h at 1150°C for BNT:0.003Pr sample. Especially, the red emission intensity of BNT:xPr3+ can be more effectively enhanced by introducing the (Bi0.5Na0.5)2+ vacancies as the charge compensation due to the formation of trapping centers, than the alkali metal ions (Li+, Na+, K+) as compensators. In addition to the intrinsic piezoelectric properties, the excitation band of BNT:xPr material can well realize the compatibility with existing blue light-emitting diode chips (450–470nm), compared to the ultraviolet or infrared light excitation luminescent materials, indicating that this system may have significant technological promise in novel multifunctional devices.

Remote-type, high-color gamut white light-emitting diode based on InP quantum dot color converters

This work reported on synthesis of highly efficient, color-pure green- and red-emitting non-Cd InP/ZnS core/shell quantum dots (QDs) and their utilization as color converters for the fabrication of display backlighting QD-based white light-emitting diode (LED). Green and red QD emitters were first individually embedded into a transparent polymeric matrix of polyvinylpyrrolidone and the resulting two free-standing QD composite plates were then physically combined into a bilayered form. White QD-LED was fabricated by remotely loading the bilayered QD plate of a red-on-green configuration onto blue LED chip. This remote-type white device generated a spectrally well-resolved, tricolored electroluminescent spectrum, and exhibited luminous efficacies of 8.9−16.7 lm/W, depending on forward currents of 20−100 mA, and a high color gamut of 87%.

High-Efficiency and Crack-Free InGaN-Based LEDs on a 6-inch Si (111) Substrate With a Composite Buffer Layer Structure and Quaternary Superlattices Electron-Blocking Layers

In this paper, a composite buffer layer structure (CBLS) with multiple AlGaN layers and grading of Al composition/u-GaN1/(AlN/GaN) superlattices/u-GaN2 and InAlGaN/AlGaN quaternary superlattices electron-blocking layers (QSLs-EBLs) are introduced into the epitaxial growth of InGaN-based light-emitting diodes (LEDs) on 6-inch Si (111) substrates to suppress cracking and improve the crystalline quality and emission efficiency. The effect of CBLS and QSLs-EBL on the crystalline quality and emission efficiency of InGaN-based LEDs on Si substrates was studied in detail. Optical microscopic images revealed the absence of cracks and Ga melt-back etching. The atomic force microscopy images exhibited that the root-mean-square value of the surface morphology was only 0.82 nm. The full widths at half maxima of the (0002) and (1012) reflections in the double crystal X-ray rocking curve were ~330 and 450 respectively. The total threading dislocation density, revealed by transmission electron microscopy, was <; 6× 108 cm-2. From the material characterizations, described above, blue and white LEDs emitters were fabricated using the epiwafers of InGaN-based LEDs on 6-inch Si substrates. The blue LEDs emitter that comprised blue LEDs chip and clear lenses had an emission power of 490 mW at 350 mA, a wall-plug efficiency of 45% at 350 mA, and an efficiency droop of 80%. The white LEDs emitter that comprised blue LEDs chip and yellow phosphor had an emission efficiency of ~110 lm/W at 350 mA and an efficiency droop of 78%. These results imply that the use of a CBLS and QSLs-EBL was found to be very simple and effective in fabricating high-efficiency InGaN-based LEDs on Si for solid-state lighting applications.

Synthesis and characterisation of CaMoO4:Eu3+, Eu3+/Sm3+, Eu3+/Sm3+/Li+ red phosphor for white LED

A series of molybdate red emitting phosphors have been successfully synthesised at 800°C by coprecipitation method. The excitation spectra of the phosphors reveal three strong excitation bands at 395, 466 and 535 nm respectively, which match well with the near UV and blue light emitting diode chips. The intensity of the emission from 5D0→7F2 of , phosphors with the optimal compositions of x = 0·04 is 1·3 times higher than that of . The photoluminescence of , (M = Li, Na, K) phosphors show the stronger emission band at 616 nm than that of , but the intensity decline with the M+ ion radius increased. In addition, the thermal quenching characteristics of CaMoO4:Eu3+, Eu3+/Sm3+, Eu3+/Sm3+/Li+ are also investigated under the temperature from 40 to 200°C, and the relative luminous intensity attenuation rate is the lowest and the thermal stability is better by doping Eu3+/Sm3+/Li+, indicating that CaMoO4:Eu3+/Sm3+/Li+ are more promising red emitting phosphors.

Tunable luminescence from Ce-doped aluminoborosilicate glasses

A series of aluminoborosilicate glasses were prepared using the melt-quenching technique for mixture of stoichiometric amounts of SiO2, Al2O3, H3BO3, Na2CO3, and ZrO2 with adding of different amounts of CeO2. The samples were investigated by means of luminescence spectroscopy. Tunable luminescence from violet to blue/green was observed from these glasses with different Xe-lamp excitation wavelengths ranging from 370 to 480 nm as well as with laser excitation of 266 and 355 nm. Moreover it was found that the possibility of tuning the light by changing of excitation wavelength was not unique. The same effect was observed by adjusting conditions for luminescence measurements as well as under exposure to β-irradiation. The obtained phenomena could be explained taking into account structural characteristics of this glass and it could be concluded that tunable luminescence results from the presence of different Ce-sites the glass matrix. Thus the results suggest that Ce-doped glasses could be considered as conversion materials for blue light-emitting diode chips to generate white light-emitting diodes.

Rare Earth Doped Lanthanum Calcium Borate Polycrystalline Red Phosphors

Single-phased Sm3+doped lanthanum calcium borate (SmxLa2−xCaB10O19, SLCB,x=0.06) polycrystalline red phosphor was prepared by solid-state reaction method. The phosphor has two main excitation peaks located at 398.5 nm and 469.0 nm, which are nicely in accordance with the emitting wavelengths of commercial near-UV and blue light emitting diode chips. Under the excitation of 398.0 nm, the dominant red emission of Sm3+in SLCB phosphor is centered at 598.0 nm corresponding to the transition of4G5/2 → 6H7/2. The Eu3+fluorescence in the red spectral region is applied as a spectroscopic probe to reveal the local site symmetry in the host lattice and, hence, Judd-Ofelt parametersΩt (t=2, 4)of Eu3+in the phosphor matrix are derived to be3.62×10-20and1.97×10-20 cm2, indicating a high asymmetrical and strong covalent environment around rare earth luminescence centers. Herein, the red phosphors are promising good candidates employed in white light emitting diodes (LEDs) illumination.

Indoor gigabit 2 × 2 imaging multiple-input–multiple-output visible light communication

We propose and experimentally demonstrate a 2 × 2 imaging multiple-input-multiple-output (MIMO) Nyquist single carrier visible light communication (VLC) system based on spectral efficient 64/32-ary quadrature amplitude modulation, as well as pre- and post-equalizations. Two commercially available red-green-blue light-emitting diodes (LEDs) with 3 dB bandwidth of 10 MHz and two avalanche photodiodes with 3 dB bandwidth of 100 MHz are employed. Due to the limited experiment condition, three different colors/wavelengths are transmitted separately. The achieved data rates of red, green, and blue LED chips are 1.5, 1.25, and 1.25 Gb/s, respectively. The resulting bit error ratios are below the 7% pre-forward error correction limit of 3.8 × 10-3 after 75 cm indoor transmission. To the best of our knowledge, this is the first experimental investigation of imaging MIMO system, and it is the highest data rate ever achieved in MIMO VLC system.

Orangish-yellow-emitting Ca3Si2O7:Eu2+ phosphor for application in blue-light based warm-white LEDs

A Eu(2+)-activated Ca3Si2O7:Eu(2+) orangish-yellow-emitting phosphor with strong luminescence was synthesized and its crystal structure was determined on the basis of XRD profiles using synchrotron radiation. The crystal structure was refined by the Rietveld refinement method. The excitation and emission spectra of the Ca3Si2O7:Eu(2+) phosphor show broad excitation bands in the range of 240-550 nm and a broad yellow emission band centered at 603 nm, depending on the concentration of Eu(2+). The optimized concentration of Eu(2+) in the Ca3Si2O7:Eu(2+) phosphor was determined to be 0.015 mol. The critical distance and average decay time were found to be short and fast, respectively, ranging from 19.74 Å to 13.69 Å and from 2.56 μs to 2.34 μs on increasing the Eu(2+) doping content. Warm-white light-emitting diodes (LEDs) fabricated using an InGaN-based blue LED chip combined with the Ca3Si2O7:0.015Eu(2+) phosphor gave color rendering indices between 76.0 and 38.9, correlated color temperatures between 1924 K and 4992 K, and tuned CIE chromaticity coordinates in the range from orangish-yellow (0.543, 0.389) to reddish purple (0.333, 0.219). The color coordinates and emission intensity of a Ca3Si2O7:0.015Eu(2+)-based white LED display were slightly yellow-shifted and the intensity increased on increasing the forward-bias current. These results indicate that orangish-yellow-emitting Ca3Si2O7:0.015Eu(2+) can serve as a promising candidate for applications in warm-white LEDs.

Strong photoluminescence and piezoelectricity properties in Pr-doped Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3 ceramics: Influence of concentration and microstructure

(Ba0.85Ca0.15)1−xPrx(Zr0.1Ti0.9)O3 (where 0 < x < 0.01, abbreviated as BCZT:xPr) ceramics were fabricated by conventional solid-state reaction method. The influence of dopant concentration and microstructure on photoluminescence, ferroelectric, and piezoelectric properties was systematically investigated. The results showed that the photoluminescence spectra of the samples exhibited strong green (530 nm) and red (602 nm) emissions upon excitation of the 430 nm to 500 nm light, which couples well with to the emission band of the commercial blue light-emitting diodes chips. The emission intensities were strongly dependent on the dopant concentration and crystallite size, which reached the optimal value when the crystallite size and dopant concentration were 8 μm and 0.002 mol, respectively. Meanwhile, a large piezoelectric response with d33 = 325 pC/N was obtained for BCZT:0.002Pr near the morphotropic phase boundary. Therefore, the Pr-doped BCZT materials, simultaneously exhibiting excellent luminescent properties and high piezoelectric properties, may have significant technological promise in novel multifunctional devices.

Fabrication of warm, high CRI white LED using non-cadmium quantum dots

We reported on the synthesis of two bright non-cadmium quantum dots (QDs) of green (512 nm)-emitting InP/ZnS and orange (583 nm)-emitting CuInS2 (CIS)/ZnS core/shell and their application for the fabrication of solid-state lighting device. The spectral overlap between absorptions from both QDs and emission from InGaN-based blue light-emitting diode (LED) chip was excellent. Thus, the efficient down-conversion of blue-to-QD emission for the generation of white light was accomplished by sequentially dispensing InP/ZnS QDs on top of CIS/ZnS ones within epoxy resin. The white QD-LED generated a high-quality white light with a high color rendering index of 90 and a warm color temperature of 3803K under a drive current of 20 mA. Drive current-dependent variations of its primary electroluminescent properties were investigated in details.

Copper Nanowires as Fully Transparent Conductive Electrodes

In pondering of new promising transparent conductors to replace the cost rising tin-doped indium oxide (ITO), metal nanowires have been widely concerned. Herein, we demonstrate an approach for successful synthesis of long and fine Cu nanowires (NWs) through a novel catalytic scheme involving nickel ions. Such Cu NWs in high aspect ratio (diameter of 16.2 ± 2 nm and length up to 40 μm) provide long distance for electron transport and, meanwhile, large space for light transmission. Transparent electrodes fabricated using the Cu NW ink achieve a low sheet resistance of 1.4 Ohm/sq at 14% transmittance and a high transparency of 93.1% at 51.5 Ohm/sq. The flexibility and stability were tested with 100-timebending by 180°and no resistance change occurred. Ohmic contact was achieved to the p- and n-GaN on blue light emitting diode chip and bright electroluminescence from the front face confirmed the excellent transparency.

Synthesis, structure and luminescence properties of TiO2:Eu3+ for white light-emitting diode

Phosphors TiO2:0.01Eu3+ were synthesized by sol–gel technology with calcination under various temperatures. Red emission with a maximum of 613nm is observed upon 465nm excitation. The excitation band just overlaps the emission band of conventional blue light-emitting diode (LED) chip, which indicates that the phosphor has potential application in white LED. The crystalline structure and lattice parameters were investigated by powder X-ray diffraction (XRD) and Rietveld refinement. The luminescence mechanism is explained simply in terms of the host crystal structure.

Photoluminescence and thermal stability of yellow-emitting Pr3+ doped CaAl2O4 phosphors

Pr 3+-doped CaAl 2 O 4 phosphors with broad yellow emission were synthesized by conventional solid-state reaction in air and their structural and luminescent properties were investigated. A pure monoclinic structure can be obtained when the sintering temperature is 1400°C or above. With photoluminescence (PL) measurement, the excitation was observed at 450–500 nm, which covered the emission of the blue light-emitting diode (LED) chips. Emission of the phosphors showed a green band and a red band. So these phosphors showed great potential in application of warm white LEDs without reabsorption. Additionally, the optimal emission intensity was obtained when Pr doping level was at 0.2 mol%. Furthermore, the Pr -doped CaAl 2 O 4 phosphors have the higher quenching temperature. With an increase in temperature, the emission bands of Pr -doped CaAl 2 O 4 showed an abnormal blue-shift.

Synthesis, characterization and luminescence properties of SrLa2(MoO4)4:Eu phosphors

SrLa2(MoO4)4 (SLM) phosphors doped with Eu3+ ions were prepared by a sol–gel combustion method using citric acid as a fuel/reductant and nitrates as oxidants. The crystallization processes were tracked by means of X-ray diffraction and thermo-gravimetric analysis and differential scanning calorimetry. The size and shape of the products were characterized using a scanning electron microscope, while the luminescent spectra of these resulting phosphors were recorded using a photoluminescence (PL) spectrophotometer. PL studies reveal that the emission intensity of SLM:Eu phosphors was strongly related to sintering temperature as well as the doping concentration of Eu3+ ions. The present phosphor has a strong excitation at 395 and 459 nm, indicating that it could serve as a promising red-emitting candidate for near-UV and GaN-based blue light-emitting diode chips.

Analysis on the Luminous Efficiency of Phosphor-Conversion White Light-Emitting Diode

The author analyzes the luminous efficiency of the phosphor-conversion white light-emitting diode (LED) that consists of a blue LED chip and a yellow phosphor. A theoretical model is derived to find the relation between luminous efficiency (LE) of a white LED, wall-plug efficiency (WPE) of a blue LED chip, and the phosphor absorption ratio of blue light. The presented model enables to obtain the theoretical limit of LE and the lower bound of WPE. When the efficiency model is applied to the measured results of a phosphor-conversion white LED, the limit theoretical value of LE is obtained to be 261 lm/W. In addition, for LE of 88 lm/W at 350 mA, the lower bound of WPE in the blue LED chip is found to be ~34%. The phosphor absorption ratio of blue light was found to have an important role in optimizing the luminous efficiency and colorimetric properties of phosphor-conversion white LEDs.

An Investigation on Eu&lt;SUP&gt;3+&lt;/SUP&gt; Doped CaLa&lt;SUB&gt;2&lt;/SUB&gt;ZnO&lt;SUB&gt;5&lt;/SUB&gt; Novel Red Emitting Phosphors for White Light-Emitting Diodes

A novel phosphor namely CaLa2ZnO5 doped with Eu3+ ions were prepared by conventional solid state reaction method. We have studied and optimized various constraints like sintering temperature, sintering time and dopant concentration. XRD, SEM profiles have been studied to explore its structural properties. Luminescence properties of these phosphors have been characterized by means of their photoluminescence (PL) spectra. We have noticed that the emission intensity of CaLa2ZnO5:Eu3+ phosphors strongly depend on its sintering temperature and Eu3+ concentration. Moreover, their PL spectra reveals that CaLa2ZnO5:Eu3+ phosphors exhibits a strong luminescence of 5D(0)_7F(2) transition at 627 nm under the excitation of 468 nm, which correspond to the popular emission line from a GaN based blue light-emitting diode (LED) chip. The obtained results of the prepared Eu3+ doped phosphors are very much encouraging and they are potentially useful in the development of new solid-state lightning devices.