Blue InGaN LEDs Research Articles

Delineating Dy3+ and Sm3+ in thermally stable strontium silicate apatites for multifunctional applications

The structural, optical and temperature dependent luminescence properties of a series of Sr2Y8-xREx(SiO4)6O2 (RE=Dy and Sm) silicate phosphors are investigated for their multifunctional applications. The phosphors were synthesized using the solid-state reaction route with varying doping levels and characterized for phase purity. X-ray Diffraction analysis revealed the hexagonal crystal structure of (Sr2RE2)(RE6)(SiO4)6O2, indicating the incorporation of rare earth (RE) ions into two distinct crystallographic sites, thereby augmenting the luminescence properties. Dy3+ doped compounds exhibit intense yellow emission, promising white light generation when paired with InGaN blue LED chips. Sm3+ doped samples show orange-red emission around 601 nm, attributed to multipole-multipole interactions, with rapid decay curves suitable for high-speed response LEDs. Correlated Color Temperature (CCT) values were computed to assess the commercial viability of these phosphors in luminescence applications and the role of lighting in the growth of indoor plants and office spaces is discussed. The Sr2Y7.8Dy0.2(SiO4)6O2 phosphor with remarkable quantum yield of 63.56% demonstrated a thermal stability of 0.27 eV with enhanced sensitivity of about 0.39% K−1 and Sr2Y7.8Sm0.2(SiO4)6O2 with stability around 0.31eV with sensitivity of 1.11% K⁻¹ at 100K reveals them as potential candidates for optical temperature sensing. These results declare the competence of synthesized novel silicate apatites in solid-state lighting and optical thermometry.

Efficient CrIII Ion Governed Energy Migration for Broadband Near‐Infrared Emission in Ca3Sc2Ge3O12 Garnet Phosphor

AbstractThe rapid growth in phosphor‐converted near‐infrared light‐emission diodes (NIR‐LEDs) has led to the development of NIR emitter with high efficiency, broadband emission and high thermal stability. In this work, an efficient broad NIR emission of Cr3+ in novel Ca3Sc2Ge3O12 (CSGO) garnet‐based host was developed for the first time, which located at 700 to 1000 nm peaking at 817 nm with a broad bandwidth of ~128 nm. Such a broadband NIR emission originated from the preferential occupancy of Cr3+ in Sc3+ sites with weak octahedral field, which was manifested by the luminescence spectrum and decay behaviors. The Cr3+‐doping concentration was regulated to achieve a good internal quantum efficiency (IQE) of 72.1 % and a fantastic thermal stability (at 423 K, sustained approximately 85 % of the initial intensity). The mechanism for concentration and thermal quenching was further investigated. Benefiting from the excellent luminescence features, a prototype NIR‐LEDs was assembled via integrating the optimized samples with commercial blue InGaN LED chips, which exhibited a satisfactory photoelectric property and a brilliant performance in night vision. These results demonstrated the as‐obtained sample to be a great potential candidate for NIR‐LEDs.

Ultrastable emissive perovskite nanocomposite via dual protection of polymer-grafted TS-1 zeolite for backlight display application

Instability of all-inorganic perovskite quantum dots (PQDs) driven by the inherent ionic nature poses a grand challenge towards their long-term stability in optoelectronic devices. Herein, we report the crafting of a highly stable dual-protected CsPbBr3 perovskite nanocomposite by capitalizing on the encapsulation of a hydrophobic Styrene-Divinylbenzene (St-Dvb) copolymer grafted hierarchical titanium silicalite-1 (TS-1) zeolite shell. Firstly, an optimal hot injection method was used to accommodate CsPbBr3 PQDs into hierarchical TS-1 zeolite. After the modification of terminated Si-OH groups on the surface of TS-1 by phenyltriethoxysilane (PTES), a subsequent polymerization of St and Dvb was implemented using azobisisobutyronitrile (AIBN) as initiator to result in the highly emissive CsPbBr3-TS@St-Dvb nanocomposite, exhibiting outstanding luminescent stability against heat, polar solvents, and UV light irradiation. The as-prepared CsPbBr3-TS@St-Dvb nanocomposite also showed strongly suppressed anion exchange and high compatibility in polymer matrix, enabling improved applicability for versatile lighting and optical display applications. Ultimately, a white light-emitting diode (WLED) composed of green-emitting CsPbBr3-TS@St-Dvb and red-emitting K2SiF6:Mn4+ phosphor onto a commercial blue InGaN LED chip with wide color gamut and excellent stability is demonstrated. This work highlights a judiciously-designed and hard-soft dual-protected strategy to produce ultrastable perovskite nanomaterials with high brightness and durability for backlight display application.

Blue LED (InGaN)-driven yellow and red emitting phosphor for white light generation

Phosphor converted white LED using a yellow and red emitting material is investigated. For this we prepare K2SiF6:Mn4+ as red emitting phosphor via wet chemical technique. The white LED (w-LED) fabricated using blue InGaN LED chip (CREE 460 nm) coated with Y3Al5O12:Ce3+ and K2SiF6:Mn4+ phosphor. The effect of K2SiF6:Mn4+ phosphor as red emitting material in combination with blue InGaN LED chip (CREE 460 nm) coated with Y3Al5O12:Ce3+ phosphor is also investigated. The Commission International de I’Eclairage (CIE) coordinates and color rendering index (CRI) were also studied as a function of K2SiF6:Mn4+ content. The w-LED fabricated using blue InGaN LED chip (CREE 460 nm) coated with Y3Al5O12:Ce3+ and K2SiF6:Mn4+ phosphor shows a CIE value (x = 0.31, y = 0.33) with 78.1 CRI.

Highly Efficient and Stable CsPbBr3-Alginic Acid Composites for White Light-Emitting Diodes

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.

Latest Advances in Narrow‐Band Phosphors and Their Role in Color Management

Latest Advances in Narrow‐Band Phosphors and Their Role in Color Management

Protonated organic cations enhance the luminescence performance and thermal stability of fluoride red phosphor K2TiF6:Mn4+

The application of red luminescent phosphors composed of Mn4+-activated fluoride in WLEDs has aroused great interest. However, most of the fluoride phosphors doped with Mn4+ have poor luminescent thermostability. In order to improve their luminescent thermostability, a new type of organic-inorganic hybrid red luminescent phosphor K2TiF6:PIPH22+,Mn4+ (PIPH22+ = protonated piperazine) was synthesized by a simple cation exchange method in this work. Protonated piperazine was incorporated into K2TiF6 lattice, and the strong hydrogen bond between H- and F- enabled the organic group to exist stably in the inorganic lattice. Compared with K2TiF6:Mn4+, the addition of PIPH22+ increases distance between adjacent [TiF6]2- and inhibits the energy migration of Mn4+ ions between [MnF6]2- to reduce nonradiative transitions. Therefore, the hybrid sample K2TiF6:PIPH22+,Mn4+ has higher emission intensity and quantum yield. Under the excitation of 467 nm blue light, K2TiF6:PIPH22+, Mn4+ exhibits sharp red emission near 631 nm, and the luminescence intensity is 2.14 times that of K2TiF6:Mn4+. K2TiF6:PIPH22+,Mn4+ has significant negative thermal quenching and higher luminescence thermostability, which can be attributed to electron-phonon interaction mechanism at high temperature. The prototype WLED prepared with YAG:Ce3+, K2TiF6:PIPH22+,Mn4+ and InGaN blue LED chip can emit warm white light (CCT = 2795 K, CRI = 91.1) under 20 mA current, and the luminescence efficiency was 105.8 Lm/W. The prototype WLED was tested under 20–120 mA current, and the results showed that the changes of CCT and CRI were stable. These results indicate the potential of K2TiF6:PIPH22+,Mn4+ in WLED applications.

Room temperature synthesis of highly stable near-infrared FAPbI3@TEOS perovskite phosphor for NIR light-emitting diodes

In some medical laboratory tests, a sampling method via intravenous injection is required. Previous research pointed out using near-infrared (NIR) light vein detectors to reduce erroneous injections. Therefore, low-cost, high-efficiency and stability NIR phosphors are highly essential. Herein, high-stability, ultrathin SiO2 wrapped NIR-CH(NH2)2PbI3 (FAPbI3) perovskite nanocrystals (NCs) are successfully manufactured via one-step method at room temperature atmospheric synthesis. By optimizing the hydrolytic condensation conditions of tetraethoxysilane (TEOS), the resulting FAPbI3@SiO2 perovskite NCs phosphors exhibits a high photoluminescence quantum yields (PLQYs) of 57.2% and improves water resistance and thermostability. The low-cost NIR light-emitting diodes (NIR-LEDs) fabricated by coating NIR-FAPbI3@SiO2 perovskite NCs phosphors on commercial blue InGaN LEDs chip demonstrated a ∼787 nm EL spectra of NIR-LEDs under the startup voltage of 2.6 V. Even after 12 h of continuous working, no significant changes were observed in the EL spectra of the NIR-LEDs, which indicates that NIR-FAPbI3@SiO2 perovskite NCs phosphor has high capacity in biological applications.

An efficient pink luminescent Eu(iii) coordination polymer excited on a blue LED chip

The design of a pink-LED device is achieved by doping an Eu(iii) coordination polymer (Eu2 CP) on an InGaN blue LED chip. The Eu2 CP has been studied systematically in terms of structure, stability and photophysical properties in the solid state.

Aqueous synthesis of 79% efficient AgInGaS/ZnS quantum dots for extremely high color rendering white light-emitting diodes

• The AgInGaS/ZnS QDs with an exceptional PL QY of 79% were successfully synthesized via microwave-assisted route, boosting the best performance of water-dispersible Ga containing I-III-VI QDs • Luminescent hydrogel films with different colors were obtained by embedding AgInGaS/ZnS QDs in PAAm/PVA hydrogel and a white LED based on the luminescent hydrogel films with a high color rendering index of 92.1 (R9=92.0) was obtained Over the past few decades, I-III-VI quantum dots (QDs) have attracted considerable attention due to their large Stokes shifts, good eco-friendliness, and wide tunable emissions. In this work, a facile microwave-assisted aqueous route using glutathione (GSH) and citric acid (CA) as dual stabilizers is introduced to synthesize AgInGaS/ZnS (AIGS/ZnS) core/shell QDs. An exceptional photoluminescence quantum yield (PL QY) as high as 79% is successfully achieved, boosting the best performance of water-dispersible AIGS QDs. By varying the Ag/Ga ratio, the PL peak wavelength can be tuned from 547 to 616 nm, and luminescent hydrogel films with different colors are obtained by embedding AIGS/ZnS QDs in polyacrylamide/ poly-vinyl alcohol (PAAm/PVA) hydrogels. The white light-emitting diode (WLED) with a high color rendering index (CRI) of 92.1 ( R 9 =92.0) and a correlated color temperature (CCT) of 3022 K is fabricated using QDs-PAAm/PVA hydrogel films in combination with a blue InGaN LED chip, indicating that the as-prepared QDs are competitive color-conversion materials for WLEDs.

High stability in color chromaticity of warm White emitting Diode with Dual-Hue SrSi2O2N2:Eu2+,Yb2+ Oxynitridosilicate Phosphorus

<span>In this study, we analyzed and developed a phosphor with a nitridiosilicate based and emitting color changing from green to orange to apply to our white-light-emitting diodes (WLEDs). Eu<sup>2+</sup> and Yb<sup>2+</sup> trap sites of two-doped SrSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2+</sup>,Yb<sup>2+</sup> (SrYb) nitridosilicate emit a wide emission in the region between green and orange. Through calculating the decompose time of the green-emission power donor, we could determine the converted energy between the active ions. Furthermore, we also analyzed the impact of co-doping with varied active ion ratios on the photoluminescence (PL) characteristics. As the concentration of Yb<sup>2+</sup> increases, the red emission dominates the green. This was because the obtained phoshor's emission depended on the activator ion components. To generate white light, a combination of the acquired phosphor and the InGaN blue LED chip with a 450 nm wavelength was used. With only two steps, we could detect the hue balance management. Firstly, by modifying the Eu<sup>2+</sup> and Yb<sup>2+</sup> concentration, we can conduct a green-to-orange proportion optimization. Following that, the commission onillumination (CIE) coordinates were transformed to [0.4071; 0.3789] from the original position, which was [0.2805; 0.2014] by enhancing the phosphor powder amount. An environment which has a CRI of around 89 is the optimum condition for conducting white light.</span>

Pulsed Sputtering Preparation of InGaN Multi-Color Cascaded LED Stacks for Large-Area Monolithic Integration of RGB LED Pixels

Micro-LEDs have been attracting attention as a potential candidate for the next generation of display technology. Here we demonstrate the feasibility of large-area monolithic integration of multi-color InGaN micro-LEDs via pulsed sputtering deposition (PSD) and a standard photolithographical technique. The PSD allows for sequential epitaxial growth of blue and green InGaN LED stacks connected with the GaN based tunneling junction. The tunneling junctions serve as protective layers on p-type GaN against the dry etching damage and hole injection layers in each blue and green emission InGaN active layer. The tunneling junction-connected multi-color InGaN LED stack contributes to the high-density and large-area monolithic integration of RGB micro-LEDs using standard photolithography and the ICP-dry etching method.

Achieving a tunable and ultra-broadband near-infrared emission in the Ga2-2xZnxGexO3:Cr3+ phosphor.

Near-infrared (NIR) spectroscopy (700-1100 nm) based on a phosphor-converted light-emitting diode (pc-LED) has multi-functional applications in bio-imaging, night-vision, and food quality analysis, simulating the development of efficient and ultra-broadband NIR phosphors. Herein, a series of tunable and ultra-broadband NIR phosphor Ga2-2xZnxGexO3:Cr3+ was successfully produced by a [Zn2+-Ge4+] unit co-substituting a [Ga3+-Ga3+] unit in Ga2O3:Cr3+. With the increasing amount of [Zn2+-Ge4+] incorporation, the emission peak can be tuned from 726 to 808 nm, and the maximum FWHM can be extended from 126 to 190 nm. However, the excitation peak position remained nearly unchanged in the blue light region, enabling this material to perfectly match the InGaN blue LED chip. Although the gradually enhanced electron-lattice coupling and low energy barrier for thermal quenching caused by this co-substitution lead to a decrease in the photoluminescence quantum yield (PLQY) and thermal stability, respectively, the absolute values of these two criteria can be well maintained. Finally, to evaluate the practical applications, prototype NIR pc-LEDs were fabricated using these materials combined with 450 nm LED chips. Under the same conditions, the NIR output power and photoelectronic conversion efficiency of these devices are superior to those fabricated using the well-known ScBO3:Cr3+ phosphor. These results demonstrate that this series of materials with tunable and ultra-broadband NIR emissions has great potential for NIR pc-LED applications.

Confining CsPbX3 perovskites in a hierarchically porous MOF as efficient and stable phosphors for white LED

Confining metal-halide perovskites within MOF hosts not only protects them from exterior environment stimulation and isolates them from each other without aggregation, but also enables a variety of new features and applications. In this work, a hierarchically porous MOF host was firstly explored for in-situ confined growth of CsPbX3 perovskite nanocrystallites (PNCs). Compared with the previously used microporous MOF matrixes, this hierarchically porous MOF not only enables the impregnation of perovskite precursors in one step, but also allows more facile diffusion of the reactants, thus giving rise to high loading capacities and uniform distribution of CsPbX3 perovskites. The MOF matrix serves as both template to guide the confined growth of monodispersed CsPbX3 PNCs and encapsulation to enhance the stability of CsPbX3 PNCs. The obtained CsPbX3@MOF nanocomposites show bright luminescence and good resistance to ambient moisture, UV light irradiation, and anion-exchange. By integrating the green-emitting CsPbBr2I@MOF and red-emitting CsPbI3@MOF nanocomposites with a commercial blue InGaN LED chip, we fabricate a primary WLED showing a NTSC value of 125% and Rec. 2020 of 93%, which highlights the potential in backlight display.

New Mg2+/Ge4+-Stabilized Gd3MgxGexAl5-2xO12:Ce Garnet Phosphor with Orange-Yellow Emission for Warm-White LEDs (x = 2.0-2.5).

By stabilization of the Gd3Al5O12 garnet by replacing 80% or more of Al3+ with Mg2+/Ge4+ pairs, a series of new orange-yellow-emitting Gd3MgxGexAl5-2xO12:Ce (x = 2.0-2.5) phosphors were successfully developed for potential application in warm-white-light-emitting diodes (WLEDs). Rietveld structure refinement proved that Mg2+ first substitutes the octahedral Al3+ ion, followed by the replacement of the tetrahedral Al3+ together with Ge4+. The band structure of the x = 2.0 typical garnet was analyzed via density functional theory (DFT) calculations. The incorporation of an increasing content of Mg2+/Ge4+ was experimentally shown to narrow the band gap and expand the unit cell of the garnet host and blue shift the emission/excitation wavelength and shorten the fluorescence lifetime of Ce3+. The photoluminescence behaviors were rationalized by considering the influence of Mg2+/Ge4+ on the crystal structure, band structure, and local coordination. An LED lamp fabricated by combining the (Gd2.97Ce0.03)Mg2Ge2AlO12 optimal phosphor with a 450 nm-emitting InGaN blue LED chip exhibited a color-rendering index of 71.6, luminous efficacy of 16.1 lm/W, and a low correlated color temperature of 2201 K under a driving current of 20 mA, indicating that phosphor may have potential application in warm WLEDs.

Local structure and luminescent properties of Cs2KGaF6:Mn4+ phosphor for backlight white LEDs

Narrow-band red-emitting phosphors are worth investigating and developing to enhance their luminescence efficiency for white light-emitting diodes (WLEDs) and broaden the color gamut of backlight displays. Herein, a novel red-emitting fluoride phosphor Cs2KGaF6:Mn4+ (CKGFM) was synthesized, which presents sharp red emission bands, short fluorescence lifetime (τ = 3.81 ms) and high external quantum efficiency (EQE = 43%). To better understand Mn4+ incorporation in CKGFM, density functional theory (DFT) energetic calculations were performed to compare the charge compensation probabilities of an Mn4+ substituted at a Ga3+ or K+ site. The temperature-dependent luminescence trend shows that the CKGFM phosphor has good thermal stability in the temperature range of 15–120 ℃, indicating its potential in backlight LEDs. The as-prepared CKGFM phosphor was used to fabricate one white light-emitting diode (WLED) with β-SiAlON:Eu2+ green phosphor and blue InGaN LED chip, which shows a high luminous efficiency of 106.30 lm∙W−1 and a National Television Standards Committee (NTSC) value of 114.6%. The present study provides detailed insights into the local structure of Mn4+ substituted in fluoride red-emitting phosphors and helps to realize better Mn4+ emission for WLEDs.

Improvement in efficiency of yellow Light Emitting Diode using InGaN barriers and modified electron injection layer

InGaN based MQW-LEDs (Multiple Quantum Well Light Emitting Diodes) are now the new generation of light sources for displays and general lightening applications. The efficiency of blue InGaN LEDs has been matured very much (>80%), but efficiency of yellow LEDs based on InGaN quantum wells still lags behind. In this paper, we have proposed a new structure for yellow LEDs based on InGaN MQW to increase the efficiency of these LEDs. A simulation approach has been used to model and simulate MQW yellow LED based on InGaN quantum wells by using k.p theory. The simulation results show that the proposed structure provides much better output characteristics than the conventional structure. Using the proposed structure, about 18% increment in internal quantum efficiency (IQE) and a decrease of about 36% in efficiency droop of the yellow LED has been successfully achieved.

Weak thermal quenching of the luminescence in the Ca3Sc2Si3O12:Ce3+garnet phosphor

We report results of the luminescence properties of the three garnet type phosphors Ce3+-doped Ca3Sc2Si3O12(CSSO:Ce3+), Sr3Y2Ge3O12(SYG:Ce3+) and Y3Al5O12(YAG:Ce3+), investigated using optical spectroscopy techniques and vacuum referred binding energy (VRBE) diagram analysis.

Synthesis and luminescent properties of novel red-emitting M7Sn(PO4)6:Eu3+(M= Sr,Ba) phosphors

Novel Eu3+-activated M7Sn(PO4)6 (where M = Sr, Ba) red-emitting phosphors were synthesized via conventional solid-state reaction method at 1200 ?C for 2 h. The luminescence properties of the prepared samples and quenching concentration of Sr7-xSn(PO4)6 :xEu3+ and Ba7-xSn(PO4)6 :xEu3+ were investigated. These phosphors can be efficiently excited by UV (395 nm) and visible blue (465 nm) light nicely matching the output wavelengths of the near-UV LEDs and InGaN blue LED chips and emit the red light. The critical concentrations of the Eu3+ activator were found to be 0.175mol and 0.21mol per formula unit for Sr7-xSn(PO4)6 :xEu3+ and Ba7-xSn(PO4)6 :xEu3+, respectively. The M7-xSn(PO4)6 :xEu3+ (M = Sr, Ba) phosphor may be a good candidate for light-emitting diodes application.

Luminescent Properties of a Cs3AlF6:Mn4+ Red Phosphor for Warm White Light-Emitting Diodes

Mn4+ activated fluoride phosphors have been considered as highly promising red component for warm white light-emitting diodes (WLEDs) in recent years. In this work, a novel nonequivalent doping Cs3AlF6:Mn4+ red-emitting phosphor were synthesized via a co-precipitation method and its crystal structure, morphology, and luminescent properties were investigated in detail. The Cs3AlF6:Mn4+ phosphor with a sheet morphology have broad band absorption in blue light region (∼467 nm) and narrow bandwidth emissions in red region (∼634 nm). The WLED fabricated with Cs3AlF6:Mn4+ red phosphor, YAG:Ce3+ yellow phosphor and a blue InGaN LED chip demonstrates intense warm light with good luminescence performance of low related color temperature (CCT, Tc = 3659 K) and high color rendering index (CRI, Ra = 86.2). These results indicate the Cs3AlF6:Mn4+ red phosphor can be a potential candidate for warm WLEDs.