Papers by Author: J.K. Park

Abstract: We have synthesized a Eu²⁺-activated Sr₂SiO₄yellow phosphor and investigated an attempt to develop white LEDs by combining it with a GaN blue LED chip. Two distinct emission bands from the GaN-based LED and the Sr₂SiO₄:Eu phosphor are clearly observed at 400 nm and at around 550 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results show that GaN (400 nm chip)-based Sr₂SiO₄:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460 nm chip)-based YAG:Ce.

Abstract: New titanium alloys with a low elastic modulus have been developed for biomedical applications to avoid the stress shielding effect of the artificial prosthesis. The newly developed alloys contained the transition elements like Nb, Ta, Zr which were non-cytotoxicity elements. These elements produced β, ω, and α'' phases with heat treatment conditions in titanium alloys and determined the elastic modulus of the alloys. However, the clear mechanism of the low elastic modulus alloys has not been known. In the present paper, the total energy and elastic modulus of β and α'' phases were calculated using a first principle calculation employing the generalized gradient approximation (GGA). The mechanism of the low elastic modulus was discussed with calculated values.