Steven Chen - Academia.edu (original) (raw)

Papers by Steven Chen

Journal of Materials Chemistry, 2012

In this study, a new efficient Ce 3+-doped fluorosulfide phosphor, Y 2 (Ca,Sr)F 4 S 2 :Ce 3+ , wa... more In this study, a new efficient Ce 3+-doped fluorosulfide phosphor, Y 2 (Ca,Sr)F 4 S 2 :Ce 3+ , was obtained by using solid-state methods in a sealed silica ampoule. The synthesized Y 2 (Ca,Sr)F 4 S 2 :Ce 3+ was characterized by powder X-ray diffraction and refined with Rietveld methods. Y 2 (Ca,Sr)F 4 S 2 :Ce 3+ can be excited by blue light (440-470 nm) and shows yellow-to-orange broadband emission peaking at 553-590 nm with a quantum efficiency of 16-31%. Non-radiative transitions between Ce 3+ ions in Y 2 CaF 4 S 2 :Ce 3+ and Y 2 SrF 4 S 2 :Ce 3+ hosts have also been demonstrated to be attributable to dipoledipole interactions, and the critical distances were calculated to be 18.9 and 19.3 A. The possible mechanism of the tunable luminescence properties was described on the basis of band structure calculations. In addition, a white LED device was fabricated by using Y 2 (Ca,Sr)F 4 S 2 :Ce 3+ phosphor pumped with a 460 nm blue chip. The CRI value and CCT were measured to be 74-85 and 3500-8700 K, respectively, showing promising potential for solid-state lighting.

Optics Express, 2010

A series of alkaline earth borophosphate phosphors, (Ba,Sr) 3 BP 3 O 12 doped with Eu 2+ ions, we... more A series of alkaline earth borophosphate phosphors, (Ba,Sr) 3 BP 3 O 12 doped with Eu 2+ ions, were synthesized by a solid state reaction. Two emission bands at 465 nm and 520 nm were attributed to the f-d transitions of doped Eu 2+ ions occupying in two different cation sites in host lattices and emission color variation was observed by substituting the M 2+ sites, which was rationalized in terms of two competing factors of the crystal field strength and bond covalence. Green and bluish-white pc-LEDs were fabricated by combination of a 370 nm near-UV chip and composition-optimized Ba 3 BP 3 O 12 :Eu 2+ and (Ba,Sr) 3 BP 3 O 12 :Eu 2+ phosphors, respectively. The series of phosphors may serve as a promising green and bluish-white luminescent materials used in fabrication of near UV-based white pc-LEDs.

Journal of Product Innovation Management, 2012

This study proposes a model of dynamic use diffusion that serves as a basis for investigating pos... more This study proposes a model of dynamic use diffusion that serves as a basis for investigating post-adoption technologyusage behavior. Dynamic use diffusion measures the extent to which technology usage has evolved since the time of adoption. Herein, antecedents and consequences of dynamic use diffusion are investigated. A large-scale, random sample survey was conducted in the United States, Sweden, and India on the use of Internet and computing technology. The survey results suggest that while the antecedents of dynamic use diffusion are similar across the three countries, the consequences are somewhat different for India. These differences can be attributed to the national cultural differences of India compared with the United States and Sweden with regard to power distance beliefs.

Thin Solid Films, 1997

To increase the nitrogen content and the degree of crystallinity in carbon nitride films by film ... more To increase the nitrogen content and the degree of crystallinity in carbon nitride films by film deposition techniques (i.e. sputtering, laser ablation etc.), a novel target material composed of carbon nitride has been prepared by UV photo-assisted synthesis. The intention is to replace the traditional graphite target with this material. This synthesis involves photo-chemical reaction of sodium amide and chloroform as carbon and nitrogen sources, respectively, followed by high temperature sintering under flowing nitrogen. Elemental analyses indicate the presence of C, N and H in the target material with a nitrogen to carbon ratio of 0.23. Infrared spectroscopy shows a mixture of sp 3 and sp 2 carbon and sp 2 nitrogen in the sintered powder. Six diffraction peaks attributable to a-C 3 N 4 were observed in XRD pattern. Grains of 0.3 mm in diameter in an extended network were also observed in the SEM micrographs. The sintered carbon nitride powder is stable up to 800°C.

Journal of Materials Chemistry, 2012

In this study, a new efficient Ce 3+-doped fluorosulfide phosphor, Y 2 (Ca,Sr)F 4 S 2 :Ce 3+ , wa... more In this study, a new efficient Ce 3+-doped fluorosulfide phosphor, Y 2 (Ca,Sr)F 4 S 2 :Ce 3+ , was obtained by using solid-state methods in a sealed silica ampoule. The synthesized Y 2 (Ca,Sr)F 4 S 2 :Ce 3+ was characterized by powder X-ray diffraction and refined with Rietveld methods. Y 2 (Ca,Sr)F 4 S 2 :Ce 3+ can be excited by blue light (440-470 nm) and shows yellow-to-orange broadband emission peaking at 553-590 nm with a quantum efficiency of 16-31%. Non-radiative transitions between Ce 3+ ions in Y 2 CaF 4 S 2 :Ce 3+ and Y 2 SrF 4 S 2 :Ce 3+ hosts have also been demonstrated to be attributable to dipoledipole interactions, and the critical distances were calculated to be 18.9 and 19.3 A. The possible mechanism of the tunable luminescence properties was described on the basis of band structure calculations. In addition, a white LED device was fabricated by using Y 2 (Ca,Sr)F 4 S 2 :Ce 3+ phosphor pumped with a 460 nm blue chip. The CRI value and CCT were measured to be 74-85 and 3500-8700 K, respectively, showing promising potential for solid-state lighting.

Optics Express, 2010

A series of alkaline earth borophosphate phosphors, (Ba,Sr) 3 BP 3 O 12 doped with Eu 2+ ions, we... more A series of alkaline earth borophosphate phosphors, (Ba,Sr) 3 BP 3 O 12 doped with Eu 2+ ions, were synthesized by a solid state reaction. Two emission bands at 465 nm and 520 nm were attributed to the f-d transitions of doped Eu 2+ ions occupying in two different cation sites in host lattices and emission color variation was observed by substituting the M 2+ sites, which was rationalized in terms of two competing factors of the crystal field strength and bond covalence. Green and bluish-white pc-LEDs were fabricated by combination of a 370 nm near-UV chip and composition-optimized Ba 3 BP 3 O 12 :Eu 2+ and (Ba,Sr) 3 BP 3 O 12 :Eu 2+ phosphors, respectively. The series of phosphors may serve as a promising green and bluish-white luminescent materials used in fabrication of near UV-based white pc-LEDs.

Journal of Product Innovation Management, 2012

This study proposes a model of dynamic use diffusion that serves as a basis for investigating pos... more This study proposes a model of dynamic use diffusion that serves as a basis for investigating post-adoption technologyusage behavior. Dynamic use diffusion measures the extent to which technology usage has evolved since the time of adoption. Herein, antecedents and consequences of dynamic use diffusion are investigated. A large-scale, random sample survey was conducted in the United States, Sweden, and India on the use of Internet and computing technology. The survey results suggest that while the antecedents of dynamic use diffusion are similar across the three countries, the consequences are somewhat different for India. These differences can be attributed to the national cultural differences of India compared with the United States and Sweden with regard to power distance beliefs.

Thin Solid Films, 1997

To increase the nitrogen content and the degree of crystallinity in carbon nitride films by film ... more To increase the nitrogen content and the degree of crystallinity in carbon nitride films by film deposition techniques (i.e. sputtering, laser ablation etc.), a novel target material composed of carbon nitride has been prepared by UV photo-assisted synthesis. The intention is to replace the traditional graphite target with this material. This synthesis involves photo-chemical reaction of sodium amide and chloroform as carbon and nitrogen sources, respectively, followed by high temperature sintering under flowing nitrogen. Elemental analyses indicate the presence of C, N and H in the target material with a nitrogen to carbon ratio of 0.23. Infrared spectroscopy shows a mixture of sp 3 and sp 2 carbon and sp 2 nitrogen in the sintered powder. Six diffraction peaks attributable to a-C 3 N 4 were observed in XRD pattern. Grains of 0.3 mm in diameter in an extended network were also observed in the SEM micrographs. The sintered carbon nitride powder is stable up to 800°C.