Phosphor & Luminescent Materials

   Phosphors and luminescent materials can convert any incident energy to the emission of electromagnetic waves in the spectrum's ultraviolet (UV), visible or infrared regions. A wide range of energy sources can stimulate material to emit luminescence, and their diversity provides convenient concepts and design approaches for luminescence phenomena and various applications.
(1) Photo-luminescence (PL; UV, Visible photons induces luminescence)
The luminescence is stimulated by UV or visible light. Moreover, it is a widely used materials science technique for characterizing dopants and impurities as emitting sites. In addition, photoluminescent materials are applied in lighting and display technologies such as fluorescent/solid-state lamps, liquid-crystal display (LCD) back-planes, and color-converting displays.
(2) Cathodo-luminescence (CL; Energetic electrons induces luminescence)
The luminescence is stimulated by energetic electrons, the name of early atomic physics experiments involving electron collision, and finds applications in lighting and display technologies such as CL lamps, Cathode ray tubes (CRT), and Field emission display (FED).
(3) Electro-luminescence (EL; Electric field induces luminescence)

Electro-luminescence involves excitation by inner electrons accelerated by an applied electric field with much lower energy than cathodoluminescence. It finds application in lighting and display technologies such as panel lighting and displays used in some liquid-crystal display (LCD) back-planes, in inorganic light-emitting diodes (LEDs), and organic light-emitting diodes (OLEDs). 

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Particle-like Nano-LED materials and Nano-LED displays

   Several hundred million individually separated p/MQW/n InGaN particle-like nano-LEDs from an InGaN-based blue (or green) wafer using a top-down method, which included a combined process of nano-patterned lithography (NSL) and dry etching. As a result, Dielectrophoresis (DEP), related to the alternating current (AC) electric field-assisted technique, was developed as an assembling process candidate to align nanorod-LEDs or Fin-LEDs. Also, Electrophoresis (EP), which is related to the direct current (DC) electric field-assisted technique, was developed as a strong assembling process candidate to align particle-like LEDs. Therefore, a combination of particle-like LED materials, a fabrication method of particle-like LEDs, and an assembly method (such as the DC offset-AC field or pulsed DC field induced DEP or EP assembly process) provides a viable approach of preferably assembling any shape of particle-like LEDs with a relatively low aspect ratio and potentially represents an essential step toward a wide range of DEP or EP-operated self-emissive nano-LED applications, such as surface lighting, scalable light (micrometers to inches), formless lighting and displays, self-emitting displays, and other innovative bio applications.  

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Quantum Dots & Nano Crystals

    Quantum dots are tiny particles or nanocrystals of a semiconducting material with diameters ranging from 2-10 nanometers. They display unique electronic and optic properties, intermediate between bulk semiconductors and discrete molecules, partly due to the unusually high surface-to-volume ratios for these particles. The most apparent result of this is fluorescence, wherein the nanocrystals can produce distinctive colors determined by the size of the particles. The excited electron can drop back into the valence band, releasing its energy by light emission. The color of that light depends on the energy difference between the conduction band and the valence band. The energy difference (color) depends on the size of QDs. 
  Potential applications of quantum dots include single-electron transistors, solar cells, LEDs, lasers, single-photon sources, second-harmonic generation, quantum computing, cell biology, and medical imaging. In our lab, semiconductor QDs and Perovskite NCs find applications in lighting and display technologies such as color-converting backlighting systems of LCDs (Quantum dot enhanced films, QDEFs) and QD-Displays (QD-OLEDs and QD-NEDs) and Quantum dot light-emitting diodes (QLEDs). 

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Circadian Rhythms: diagnosis and therapy  

   Circadian rhythms are biological patterns within approximately 24 hours. Human sleep patterns are generally managed and entrained by the endogenous circadian clock, which consists of the central circadian clock in the suprachiasmatic nucleus (SCN) and the peripheral clocks in the organs, muscles, and bones, as shown in Figure. While the inputs of the circadian clock are numerous, external and internal time cues (Zeitgebers) such as light, eating, and human activity, the outputs are the metabolization of the organs, muscles, and bones, as well as physiological phenomena such as sleep-awakening, blood pressure, heart rate, respiration rate, and hormone secretion. These outcomes may be synchronized and oscillated periodically under exposure to natural light according to the Earth's rotation cycle (day and night), and they account for a healthy human life. Therefore, the inter-daily stability (IS) and intraday variability (IV) of biological signals such as the brain wave, heart rate, core body temperature, and melatonin hormone that helps deep sleep can be analyzed as circadian rhythm markers. However, in the modern lifestyle, overexposure to electric light at night, abuse of electronic devices such as smartphones, virtual reality, and TV, coupled with irregular exposure to indoor lighting, has disrupted the circadian rhythm. The direct consequences are the suppression of melatonin, sleep disorder, and, in part, the burden of breast cancer.
  As such, we should pay more attention to the fact that the blue light from displays is in the range of a longer wavelength (lower energy) than the wavelength causing the retina damage problem. In other words, the blue light emitted from the display coincides with the wavelength range of light that affects the circadian rhythm disturbance. Therefore, more focus should be on the physiological issues caused by blue emissions from displays, such as the suppression of melatonin secretion, circadian phase disruption, and sleep disorders, rather than photochemical problems. 
  Although further studies are required, such as obtaining more clinical data for higher statistical confidence and establishing rigorous standards for a fairer and more scientific comparison, our preliminary result already shows evidence that the effects of CIL on locomotor activity, sleep disorder, EEG, HRV, melatonin, and circadian rhythm play roles of essential and valuable performance metrics for human-centric display/lighting. Our results also suggest that healthful displays/lightings feasible by reducing CIL, maintaining the image quality and energy efficiency at the same level, and employing the time-varying user-customized CIL, healthful displays/lightings are feasible.

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