Naoki Kimura

2-phosphor-converted white light-emitting diodes using oxynitride/nitride phosphors

Green α-sialon:Yb2+ and red Sr2Si5N8:Eu2+ oxynitride/nitride phosphors have been demonstrated as potential downconversion luminescent materials for white light-emitting diodes (LEDs). In this letter, the authors attempt to fabricate white LEDs by combining α-sialon:Yb2+ and Sr2Si5N8:Eu2+ with a blue LED die and report their optical properties. These two phosphors lend themselves for use in 2-phosphor-converted white LEDs with promising properties: a wide range of tunable correlated color temperature (2700–6700K), acceptable color rendering index (82–83), and luminous efficacy (17–23lm∕W). These LEDs are acceptable for general lighting.

Wavelength-tunable and thermally stable Li-α-sialon:Eu2+ oxynitride phosphors for white light-emitting diodes

Eu2+-activated Li-α-sialon is a promising yellow phosphor for white light-emitting diodes (LEDs). This letter reports that the emission of Eu2+ in Li-α-sialon can be tuned widely (563–586nm) by tailoring the composition or controlling the Eu2+ concentration. The thermal stability of Li-α-sialon:Eu2+, relying a little on the composition and the Eu2+ concentration, remains high in a wide temperature range (25–200°C). Moreover, the chromaticity of Li-α-sialon:Eu2+ does not shift with changes in temperature. Using a single Li-α-sialon:Eu2+ phosphor, highly efficient white LEDs (46–55lm∕W) with different color temperatures (3000–5200K) can be fabricated.

Extrahigh color rendering white light-emitting diode lamps using oxynitride and nitride phosphors excited by blue light-emitting diode

The blue-light-excitation-type white light-emitting diode (LED) lamps are considered to be very suitable for lighting for art objects, shop window displays, and medical applications because they do not give infrared ray and ultraviolet ray. But their color rendering indices are needed to be improved for such applications. In this letter, the authors have fabricated white LED lamps with a broad range of color temperatures, and realized extrahigh color rendering index Ra values of 95–98 in them, using four oxynitride/nitride phosphors and a blue LED die. It means UV LED die is not always necessary for high color rendering white LED lamps. The luminous efficacies of white LED lamps are 28–35lm∕W, which are sufficiently high for extremely high color rendering white LED lamps.

Warm-white light-emitting diode with yellowish orange SiAlON ceramic phosphor

A warm-white light-emitting diode (LED) without blending of different kinds of phosphors is demonstrated. An approach that consists of a blue LED chip and a wavelength-conversion phosphor is carried out. The phosphor is a newly developed yellowish orange CaEuSiAlON ceramic phosphor with high efficiency. The CIE1931 chromaticity coordinates (x, y) are (0.458, 0.414), the color temperature is 2750 K, and the luminous efficacy of this LED is 25.9 lm/W at room temperature and with a forward-bias current of 20 mA. The chromaticity of the assembled LED is more thermally stable than that of a LED with a conventional oxide phosphor (YAG:Ce) because of the better thermal stability of the oxynitride phosphor.

White light-emitting diodes (LEDs) using (oxy)nitride phosphors

(Oxy)nitride phosphors have attracted great attention recently because they are promising luminescent materials for phosphor-converted white light-emitting diodes (LEDs). This paper reports the luminescent properties of (oxy)nitride phosphors in the system of M–Si–Al–O–N (M = Li, Ca or Sr), and optical properties of white LEDs using a GaN-based blue LED and (oxy)nitride phosphors. The phosphors show high conversion efficiency of blue light, suitable emission colours and small thermal quenching. The bichromatic white LEDs exhibit high luminous efficacy (~55 lm W−1) and the multi-phosphor converted white LEDs show high colour rendering index (Ra = 82–95). The results indicate that (oxy)nitride phosphors demonstrate their superior suitability to use as down-conversion luminescent materials in white LEDs.

White Light-Emitting Diode Lamps Using Oxynitride and Nitride Phosphor Materials

White-light emitting diode lamps for general illumination can be realized by a combination of a blue light-emitting diode semiconductor die and phosphors. Newly developed oxynitride and nitride phosphors are promising candidates for this application because they have suitable excitation and emission wavelengths and stable optical properties in a high temperature environment. High brightness warm-white LED lamps have been realized using a yellowish-orange α-SiAlON oxynitride phosphor. High color-rendering index white LED lamps have been also realized using three color oxynitride/nitride phosphors.

Optical Camera Link cable for the industrial applications

We present the development of an active optical cable (AOC) for the Camera Link interface, in which our compact optical assembly structure has been applied. The optical Camera Link cable enables the transmission of a high resolution image more than 10 m which has been the maximum transmission length for conventional metal cables.

Tunable second order dispersion compensator using fiber Bragg grating with double ring structure

Tunable second order dispersion compensator is realized utilizing linear chirped FBG with double ring structure. Tunable range from -100 to 100 ps/nm/sup 2/ is achieved in keeping center wavelength and first order dispersion constant.