The effectiveness of MgCeAl11O19:Tb3+ phosphor in enhancing the luminous efficacy and color quality of multi-chip white LEDs

In this research paper, we introduced yellow-green MgCeAl11O19:Tb3+ asa new phosphor ingredient to adapt to the quality requirements onthe chromatic homogeneity and emitted luminous flux of modern multi-chip white LED lights (MCW-LEDs). The results from experiments and simulation show that employing MgCeAl11O19:Tb3+ phosphor can lead to much better optical properties and therefore is a perfect supporting material to achieve the goals of the research. When the MgCeAl11O19:Tb3+ phosphor is added into the phosphorus composite which already contains YAG: Ce3+ particles, and the silicone glue, it affects the optical properties significantly. In other words, the concentration of this phosphor can determine the efficiency of lumen output and chromatic homogeneity of WLEDs. In specific, as the concentration of MgCeAl11O19:Tb3+ go up, the luminous yield will increase accordingly, though there is an insignificant decrease in CQS. Moreover, if the MgCeAl11O19:Tb3+ concentration reduce a little bit, it is possible to better the correlated color temperature uniformity and lumen efficacy of LED packages. In addition, the Mie scattering theory, Monte Carlo simulation and LightTools 8.3.2 software are employed to analyze and simulate the LED packages’ structure as well as the phosphor compound

Enhance the chromatic uniformity and luminous efficiency of WLEDs with triple-layer remote phosphor structures

The angular color uniformity (ACU) with the ability to evaluate chromatic performance of WLED has become an important target to achieve in producing higher-quality WLEDs. This paper studies the ACU enhancing effects of novel triple-phosphor configuration in lighting devices with remote phosphor structure. Moreover, the optical influences of remote phosphor structure with three phosphor layers (TL) on WLEDs properties are calculated and compared to the dual-layer (DL) one for reference. The experiments are applied to devices at 5 distinct correlated color temperature ranging from 5600-8500 K. The results presented that DL structure attains better color rendering index (CRI) than the TL one. Meanwhile, in terms of color quality scales (CQS), TL model shows higher values at all ACCTs, compared to the DL. Moreover, the luminous flux of DL configuration is lower than that of TL structure. In addition, the diversion of color temperature depicts as D-CCT in TL structure is much better than the value in DL structure, especially at high ACCT as 8500 K, which means TL is good for chromatic uniformity of high ACCTs WLEDs. These results proved that the triple-layer structure is superior and more effective to apply for acquiring the enhancement of WLEDs package

Combination of up-converting materials with semiconductor light sources

Methods, apparatus and systems for an up-converter resonant cavity light emitting diode device includes a semiconductor light source, an up-converter to form the light emitter with up-converting materials and an electrical source coupled with the semiconductor light source for providing electrical energy to the semiconductor light source to provide a desired wavelength emitted light. The semiconductor light source is a resonant cavity light emitting diode or laser that emits an approximately 975 nm wavelength to provide electrical and optical confinement to the semiconductor light source to form an up-converting resonant cavity light emitting diode (UCIRCLED). Rows and columns of electrodes provide active matrix addressing of plural sets of UCIRCLEDs for display devices. The up-converter resonant cavity light emitting diode device has applications in head mounted projection display optical system using spectrally selective beam splitters to eliminate spectral overlap between colors a

New generation light emitting diodes:fundamentals and applications

Light emitting diodes (LEDs) have made tremendous progress in last 15 years andhave reached to a point where they are reinventing and redefining artificial lighting.The efficiency and better control over light quality parameters have been the keyattributes of LEDs that makes them better than the existing lighting solutions.Nevertheless, in their own realm they suffer from decrease in efficiency at highercurrents, i.e. the “efficiency droop” phenomenon. Thus, a better understandingof the mechanisms leading to droop is of utmost importance. Moreover, the fullpotential in terms of light quality, i.e. colour rendering index (CRI) and correlatedcolour temperature (CCT) that can be offered by these devices can be furtherimproved with existing or alternative schemes and device configurations.In this thesis, a novel phosphor covered approach is investigated towards improvingthe CRI for indoor lighting applications. A monolithic di-chromatic LEDemitting at blue and cyan wavelengths is used to pump a green-red phosphor mixtureand a warm (CCT ∼ 3400 K) white light with a superior CRI of 98.6 is achieved.An alternate phosphor free solution to achieve warm white light emission is alsostudied. These monolithic di-chromatic QW devices emitting at blue and greenwavelengths under electrical pumping demonstrated tuneable emission from cool(CCT ∼ 22000 k) to warm (CCT ∼ 5500 K) white light. A maximum CRI of 67,which is the highest value demonstrated for such devices till date to the best of myknowledge, is also achieved.On the subject of efficiency of LEDs, temperature dependence of LEE andIQE of commercial InGaN/GaN based blue LED is studied in light of a step-wiseprocessing procedure based on the ABC-model to determine these quantities. Adecrease in both IQE and LEE with temperature is noted. On the other hand,efficiency decrease in the investigated AlGaInP based red LEDs under pulsed currentshows a shift in the onset of efficiency decrease towards higher current values withdecreasing pulse width with < 1% duty cycle. For sub-nanosecond pulses a linearrelation between applied peak current and peak output power is obtained. Theseobservations indicate device self-heatin

Composite cavity for enhanced efficiency of up conversion.

Methods, apparatus and systems for an up-converter resonant cavity light emitting diode device includes a semiconductor light source, an up-converter to form the light emitter with up-converting materials and an electrical source coupled with the semiconductor light source for providing electrical energy to the semiconductor light source to provide a desired wavelength emitted light. The semiconductor light source is a resonant cavity light emitting diode or laser that emits an approximately 975 nm wavelength to provide electrical and optical confinement to the semiconductor light source to fonn a resonant cavity up-converting light emitting diode (UCIRCLED). Rows and columns of electrodes provide active matrix addressing of plural sets of UC/RCLEDs for display devices. The up-converter resonant cavity light emitting diode device has applications in head mounted projection display optical system using spectrally selective beam splitters to eliminate spectral overlap between colors a

Composite cavity for enhanced efficiency of up conversion.

Methods, apparatus and systems for an up-converter resonant cavity light emitting diode device includes a semiconductor light source, an up-converter to form the light emitter with up-converting materials and an electrical source coupled with the semiconductor light source for providing electrical energy to the semiconductor light source to provide a desired wavelength emitted light. The semiconductor light source is a resonant cavity light emitting diode or laser that emits an approximately 975 nm wavelength to provide electrical and optical confinement to the semiconductor light source to fonn a resonant cavity up-converting light emitting diode (UCIRCLED). Rows and columns of electrodes provide active matrix addressing of plural sets of UC/RCLEDs for display devices. The up-converter resonant cavity light emitting diode device has applications in head mounted projection display optical system using spectrally selective beam splitters to eliminate spectral overlap between colors a

Epitaxial growth of iii-nitride nanostructures and their optoelectronic applications

Light-emitting diodes (LEDs) using III-nitride nanowire heterostructures have been intensively studied as promising candidates for future phosphor-free solid-state lighting and full-color displays. Compared to conventional GaN-based planar LEDs, III-nitride nanowire LEDs exhibit numerous advantages including greatly reduced dislocation densities, polarization fields, and quantum-confined Stark effect due to the effective lateral stress relaxation, promising high efficiency full-color LEDs. Beside these advantages, however, several factors have been identified as the limiting factors for further enhancing the nanowire LED quantum efficiency and light output power. Some of the most probable causes have been identified as due to the lack of carrier confinement in the active region, non-uniform carrier distribution, and electron overflow. Moreover, the presence of large surface states and defects contribute significantly to the carrier loss in nanowire LEDs. In this dissertation, a unique core-shell nanowire heterostructure is reported, that could overcome some of the aforementioned-problems of nanowire LEDs. The device performance of such core-shell nanowire LEDs is significantly enhanced by employing several effective approaches. For instance, electron overflow and surface states/defects issues can be significantly improved by the usage of electron blocking layer and by passivating the nanowire surface with either dielectric material / large bandgap energy semiconductors, respectively. Such core-shell nanowire structures exhibit significantly increased carrier lifetime and massively enhanced photoluminescence intensity compared to conventional InGaN/GaN nanowire LEDs. Furthermore, AlGaN based ultraviolet LEDs are studied and demonstrated in this dissertation. The simulation studies using Finite-Difference Time-Domain method (FDTD) substantiate the design modifications such as flip-chip nanowire LED introduced in this work. High performance nanowire LEDs on metal substrates (copper) were fabricated via substrate-transfer process. These LEDs display higher output power in comparison to typical nanowire LEDs grown on Si substrates. By engineering the device active region, high brightness phosphor-free LEDs on Cu with highly stable white light emission and high color rendering index of \u3e 95 are realized. High performance nickel?zinc oxide (Ni-ZnO) and zinc oxide-graphene (ZnO-G) particles have been fabricated through a modified polyol route at 250?C. Such materials exhibit great potential for dye-sensitized solar cell (DSSC) applications on account of the enhanced short-circuit current density values and improved efficiency that stems from the enhanced absorption and large surface area of the composite. The enhanced absorption of Ni-ZnO composites can be explained by the reduction in grain boundaries of the composite structure as well as to scattering at the grain boundaries. The impregnation of graphene into ZnO structures results in a significant increase in photocurrent consequently due to graphene\u27s unique attributes including high surface area and ultra-high electron mobility. Future research directions will involve the development of such wide-bandgap devices such as solar cells, full color LEDs, phosphor free white-LEDs, UV LEDs and laser diodes for several applications including general lighting, wearable flexible electronics, water purification, as well as high speed LEDs for visible light communications

Study of the III-nitride materials grown by mixed-source HVPE for white LED applications emitting multi spectrum range

The purpose of this study is to explore the possibility of phosphor-free white-emitting LED？s based in the gallium nitride material system. The structures are to be grown using mixed source hydride vapor phase epitaxy (MS-HVPE). It is unique crystal growth technology different from conventional HVPE and MOCVD system using mixed metal source of aluminum, indium and gallium. The first step in this project is the optimization of MS-HVPE growth process. This was achieved successfully, as binary, ternary and quaternary films are demonstrated. Successful n and p-type doping are also demonstrated introducing Te and Mg. The second step in this project is fabricating broadband spectrum emitting device of phosphor-free white LED by MS-HVPE. The device structure consisted of conventional double-hetero (DH) structure, which was the undoped InAlGaN active layer and n, p-AlGaN cladding layers. We observed that the device of AlInGaN quarternary active grown by MS-HVPE emitted multi spectrum from UV to red area. We also found that its spectrum was variable as indium mole fraction and controllable. It was nano phase epitaxy phenomenon being only observed in HS-HVPE process. An extensive growth study of GaN based material was also carried out. The effects of several growth parameters on emission characteristics were presented. PL emission wavelengths for each structure were demonstrated. And EL emission wavelengths were also demonstrated after wafer fabrication process. Additionally, x-ray diffraction and x-ray photoelectron spectroscopy (XPS) showed to verify crystal quality of MS-HVPE. The dissertation presented herein demonstrates achieving phosphor-free solid-state white lighting. But it still has unknown physical characteristics. Continuation of this study will lead to future industry. And hopefully it will be commercialized and applied to residential illumination due to this technology.Chapter 1. Introduction 1 1.1. Overview of LED 1 1.2. Wide bandgap compound semiconductor 6 1.3. Overview of white LED 10 1.4. Purpose and outline of this project 15 Chapter 2. Fundamentals of Gallium Nitride 21 2.1. Introduction 21 2.1.1. Current Issues in GaN-based LED 23 2.2. Crystallography of Gallium Nitride 26 2.3. Characteristics of Gallium Nitride 32 2.3.1. Doping of Gallium Nitride 33 2.3.2. Optical Properties of Gallium Nitride 35 2.3.3. Polarity in Gallium Nitride 38 2.4. Substrates for GaN Epitxial Growth 40 2.4.1. Substrate issues 40 2.4.2. Sapphire 41 2.4.3. SiC 45 Chapter 3. Overview of Epitaxial Growth Experimental 57 3.1. Hydride vapor phase epitaxy 57 3.1.1. Introduction to HVPE 57 3.1.2. Mixed source HVPE system 59 3.1.3. Some parameters for optimized GaN growth 62 3.2. Wafer fabrication process 63 3.2.1. Selective area growth 63 3.2.2.Metallization of GaN 64 3.3. Measurements 66 3.3.1. Photoluminescence 66 3.3.2. DXRD 67 3.3.3. SEM/CL 70 3.3.4. E-CV 75 3.3.5. Hall measurement 77 Chapter 4. Mixed Source HVPE Growth Experiment for Bulk Characteristics 82 4.1. GaN growth 82 4.1.1 Buffer growth for GaN layer 83 4.1.2. Mg-doped GaN layer 87 4.2. AlGaN growth 90 4.3. InGaN growth 97 Chapter 5. Fabrication of AlInGaN-Based LED for White Emission 115 5.1. AlInGaN SAG-DH structure growth 115 5.2. Characterization of AlInGaN SAG-DH epitaxial structure 123 5.3. Device fabrication 127 Chapter 6. Experimental Results for Active layer’s Condition 135 6.1. Performance of AlInGaN white LED 136 6.2. EL characteristics of AlGaN and AlInGaN active 139 6.2.1 GaN active layer 139 6.2.2 Al(0.1g)GaN active layer 141 6.2.3 Al(0.3g)GaN active layer 144 6.2.4 Al(0.4g)GaN active layer 144 6.2.5 Al(0.5g)GaN active layer 146 6.2.6 Al(0.6g)GaN active layer 149 6.2.7 In(0.1g) Al(0.6g) GaN active layer 151 6.2.8 In(0.2g)Al(0.6g)GaN active layer 153 6.2.9 In(0.3g)Al(0.6g)GaN active layer 155 6.2.10 In(0.4g)Al(0.6g)GaN active layer 158 6.2.11 In(0.5g)Al(0.6g)GaN active layer 160 6.3. XRD characteristics 163 Chapter 7. Phosphor &#8211Free White LED Lamp 180 7.1. Manufacturing of white LED lamp 180 7.2. Analysis of White LED Spectra and Color Rendering 181 7.3. Measurement of Phospohor free white LED 189 7.4. Future research 197 Chapter 8. Conclusions 200 Publications 202 Conference 204 Biography 209 Acknowledgements 21