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Crystals
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Recent Advances in Light-Emitting Diodes (LEDs)
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Recent Advances in Light-Emitting Diodes (LEDs)

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (31 October 2019) | Viewed by 38330

Special Issue Editor

Prof. Dr. Jaehee Cho

E-Mail Website
Guest Editor
School of Semiconductor and Chemical Engineering, Chonbuk National University, Jeonju 54896, Republic of Korea
Interests: photonics; optoelectronics; light-emitting diode; laser diode

Special Issue Information

Dear Colleagues,

This Special Issue on “Recent Advances in Light-Emitting Diodes (LEDs)” is intended to open discussions on solid-state light emitters, such as inorganic LEDs and organic LEDs (OLEDs), and highlight recent progress and trends in this field. The availability of such devices emitting in the wide spectral range, including ultraviolet, visible, infrared, and white, enables a variety of applications in signages, displays, automobiles, general lighting, telecommunications, sterilization, biology, and urban farming. Novel materials and device architectures combined with advanced manufacturing processes have promised reliable solid-state light emitters with refined color reproduction, high efficiency, and high luminous flux. Further progress requires innovations in both materials and devices. In this Special Issue, regular articles related to material and device features as well as to fabrication and applications of LEDs and OLEDs are invited to convey the current state of the art of efficiency, spectral quality, reliability, new applications, and other relevant technical aspects of LEDs and OLEDs. Communications, comments, perspectives, and reviews are welcome.

Dr. Jaehee Cho
Guest Editor

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Keywords

  • light-emitting diode (LED)
  • organic LED (OLED)
  • hybrid LED (i.e., perovskite LED)
  • ultraviolet, visible, infrared, and white LED/OLED
  • micro LED and micro LED display
  • flexible, foldable, and printable LED/OLED
  • solid-state lighting
  • compound semiconductor
  • luminescent materials

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Published Papers (6 papers)

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Research

9 pages, 2546 KiB  
Article
Investigating the Efficiency Droop of Nitride-Based Blue LEDs with Different Quantum Barrier Growth Rates
by C. K. Wang, Y. Z. Chiou and H. J. Chang
Crystals 2019, 9(12), 677; https://doi.org/10.3390/cryst9120677 - 17 Dec 2019
Cited by 5 | Viewed by 2846
Abstract
In this study, GaN-based blue InGaN/GaN light-emitting diodes (LEDs) with different growth rates of the quantum barriers were fabricated and investigated. The LEDs with quantum barriers grown with a higher growth rate exhibit a lower leakage current and less non-radiative recombination centers in [...] Read more.
In this study, GaN-based blue InGaN/GaN light-emitting diodes (LEDs) with different growth rates of the quantum barriers were fabricated and investigated. The LEDs with quantum barriers grown with a higher growth rate exhibit a lower leakage current and less non-radiative recombination centers in the multiple quantum wells (MQWs). Therefore, the LED with a higher barrier growth rate achieves a better light output power by 18.4% at 120 mA, which is attributed to weaker indium fluctuation effect in the QWs. On the other hand, the localized states created by indium fluctuation lead to a higher local carrier density, and Auger recombination in the QWs. Thus, the efficiency droop ratio of the LEDs with a higher barrier growth rate was only 28.6%, which was superior to that with a lower barrier growth rate (39.3%). Full article
(This article belongs to the Special Issue Recent Advances in Light-Emitting Diodes (LEDs))
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14 pages, 6535 KiB  
Article
Research on Luminance Distributions of Chip-On-Board Light-Emitting Diodes
by Dariusz Czyżewski
Crystals 2019, 9(12), 645; https://doi.org/10.3390/cryst9120645 - 5 Dec 2019
Cited by 17 | Viewed by 3621
Abstract
Chip-On-Board Light-Emitting Diodes (COB LED) are increasingly more common. Their development in recent years has directly contributed to increasing the power of LED sources, whilst simultaneously increasing the luminous flux from the entire COB. Consequently, it has led to new developments in some [...] Read more.
Chip-On-Board Light-Emitting Diodes (COB LED) are increasingly more common. Their development in recent years has directly contributed to increasing the power of LED sources, whilst simultaneously increasing the luminous flux from the entire COB. Consequently, it has led to new developments in some applications. Information regarding the size of the light source luminous surface and luminance distribution on its surface is critical for a designer whilst designing optical systems. The purpose of this conducted research was to establish to what extent luminance distribution is even on the examined COB LEDs. In order to verify luminance distributions on an LED surface, direct measurements with a matrix luminance measuring device were made. As a result of the research, it has been observed that luminance distribution is not even, and in many cases luminance maximum does not fall in the geometric center of the luminous surface, which was initially expected. So, it has been concluded that while designing optical systems for COB LEDs, irregular luminance distribution on their surface needs to be considered. Full article
(This article belongs to the Special Issue Recent Advances in Light-Emitting Diodes (LEDs))
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8 pages, 1932 KiB  
Article
In Situ Synchrotron X-ray Diffraction Reciprocal Space Mapping Measurements in the RF-MBE Growth of GaInN on GaN and InN
by Tomohiro Yamaguchi, Takuo Sasaki, Seiji Fujikawa, Masamitu Takahasi, Tsutomu Araki, Takeyoshi Onuma, Tohru Honda and Yasushi Nanishi
Crystals 2019, 9(12), 631; https://doi.org/10.3390/cryst9120631 - 28 Nov 2019
Cited by 6 | Viewed by 4711
Abstract
In this work, in situ synchrotron X-ray diffraction reciprocal space mapping (RSM) measurements were carried out for the radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE) growth of GaInN on GaN and InN layers, which were also grown by RF-MBE on commercialized GaN/c-sapphire [...] Read more.
In this work, in situ synchrotron X-ray diffraction reciprocal space mapping (RSM) measurements were carried out for the radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE) growth of GaInN on GaN and InN layers, which were also grown by RF-MBE on commercialized GaN/c-sapphire templates. In situ XRD RSM measurements were performed using an MBE apparatus directly coupled to an X-ray diffractometer at the beamline of the synchrotron radiation facility SPring-8. It was observed in situ that both lattice relaxation and compositional pulling occurred during the initial growth stage, reducing the strain of GaInN on GaN and InN. Different initial growth behaviors of GaInN on GaN and InN were also observed from the results of the evolution of GaInN integrated peak intensities. Full article
(This article belongs to the Special Issue Recent Advances in Light-Emitting Diodes (LEDs))
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17 pages, 5395 KiB  
Article
LED as Transmitter and Receiver of Light: A Simple Tool to Demonstration Photoelectric Effect
by Giuseppe Schirripa Spagnolo, Fabio Leccese and Mariagrazia Leccisi
Crystals 2019, 9(10), 531; https://doi.org/10.3390/cryst9100531 - 15 Oct 2019
Cited by 21 | Viewed by 16431
Abstract
The experimental observations of the photoelectric effect show the properties of quantum mechanics of the electromagnetic field. For this reason, this important effect is commonly used as an introductory topic for the study of quantum physics. The “classical” demonstration of the photoelectric effect [...] Read more.
The experimental observations of the photoelectric effect show the properties of quantum mechanics of the electromagnetic field. For this reason, this important effect is commonly used as an introductory topic for the study of quantum physics. The “classical” demonstration of the photoelectric effect is very incisive; unfortunately, the experimental apparatus is not cheap and easy to realize. The typical use of LEDs is as light emitters, but they can be used even as photosensors and, in this case, they are sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. Furthermore, a LED used as detector is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. This ability of LEDs offers the possibility of developing a simple tool able to demonstrate the photoelectric effect. This paper describes the realization of an economic, simple, easy and safe system to use for the experimental demonstration of the photoelectric effect, based on the LED to LED structure. The paper has educational purposes, oriented towards laboratory teaching activities. Full article
(This article belongs to the Special Issue Recent Advances in Light-Emitting Diodes (LEDs))
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7 pages, 3115 KiB  
Article
High Stability LED-Pumped Nd:YVO4 Laser with a Cr:YAG for Passive Q-Switching
by Hong Xiao, Tianzhuo Zhao, Wenqi Ge, Qixiu Zhong, Mingshan Li, Jiaqi Yu, Zhongwei Fan, Shengwei Bian and Yanzhong Chen
Crystals 2019, 9(4), 201; https://doi.org/10.3390/cryst9040201 - 10 Apr 2019
Cited by 5 | Viewed by 5892
Abstract
With improvements in light-emitting diode (LED) performance and a sharp decline in price, a light source with the irradiance of a laser and the cost of an LED is worthy of further study. We demonstrated a LED-pumped Nd:YVO4 laser in quasi-continuous-wave (QCW) [...] Read more.
With improvements in light-emitting diode (LED) performance and a sharp decline in price, a light source with the irradiance of a laser and the cost of an LED is worthy of further study. We demonstrated a LED-pumped Nd:YVO4 laser in quasi-continuous-wave (QCW) and passively Q-switched (PQS) regime. With an incident pump energy of 6.28 mJ (150 μs pulses at 1 Hz), the Nd:YVO4 laser has an energy of 206 μJ at 1064 nm in the QCW regime. The optical conversion efficiency of the system is 4.1%, and the slope efficiency is 9.0%. A pulsed energy of 2.5 μJ was obtained with a duration of 897 ns (FWHM) in the PQS regime, which means the peak power is 2.79 W. The output energy stability is 97.54%. Full article
(This article belongs to the Special Issue Recent Advances in Light-Emitting Diodes (LEDs))
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13 pages, 1223 KiB  
Article
Power Allocation Optimization Design for the Quadrichromatic LED Based VLC Systems with Illumination Control
by Yu Zuo, Jian Zhang and Jing Qu
Crystals 2019, 9(3), 169; https://doi.org/10.3390/cryst9030169 - 22 Mar 2019
Cited by 4 | Viewed by 3189
Abstract
For requiring high communication rate and high-quality illumination, multi-color light-emitting diodes (LEDs) have been utilized in visible light communication (VLC) systems and attracted substantial research interests. It should be noted that multiple colors are not independent from each other since they are jointly [...] Read more.
For requiring high communication rate and high-quality illumination, multi-color light-emitting diodes (LEDs) have been utilized in visible light communication (VLC) systems and attracted substantial research interests. It should be noted that multiple colors are not independent from each other since they are jointly limited by the chromaticity constraint. Thus, taking full consideration of the multi-color crosstalk problem and actual communication and illumination constraints, this paper formulates a power-efficient illumination control optimization design to reduce power consumption for the quadrichromatic LED (QLED) based VLC systems where signal to interference plus noise ratio (SINR) and quadrangle chromaticity tolerance region constraints should be satisfied. Simulation results illustrate that our proposed optimal power allocation strategy can significantly increase power efficiency for the VLC system compared with the uniform power allocation method. Moreover, the proposed scheme can provide optimal performance under different given correlated color temperature (CCT) values. Full article
(This article belongs to the Special Issue Recent Advances in Light-Emitting Diodes (LEDs))
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