Mingming Shi

Preparation and characterization of a new long afterglow phosphor CaSnO3: Yb3+

A new phosphor CaSnO3: Yb3+ was synthesized by a traditional solid-state reaction and the luminescent properties were investigated. The phosphors are well crystallized at 1200 °C. The excitation and the emission spectra show the characteristic broad of the Sn2+ ion and the X-ray photoelectron spectroscopy demonstrate the existence of Sn2+ ions caused by the doping of Yb3+ ions. The CaSnO3: Yb3+ phosphor showed a typical afterglow behavior when the UV source was switched off. Thermal simulated luminescence study indicated that the persistent afterglow of CaSnO3: Yb3+ phosphor was generated by the suitable electron or hole traps which were resulted from doping the calcium stannate host with rare-earth ions (Yb3+).

Optical and electrical properties of a spiral LED filament

This paper introduces a new type of spiral white light-emitting diodes (WLED) filament with high luminous efficiency and uniform optical performance. The optical and thermal properties of the flexible filament were investigated at different stretching heights, namely 0, 1, 2, and 3 cm. The results indicated that the filament showed the best optical characteristics at the stretching height of 2 cm, because of good heat dissipation. In addition, the radiation temperature of the filament was inversely proportional to the output luminous flux. The reliability of the filament at a stretching height of 2 cm was also evaluated after 1000 h of use. The result demonstrated that the luminous flux decay of the bulb was only 0.85%. The flexible spiral WLED filament exhibiting high luminous flux and good reliability could be adapted to promote industrial development in the near future.

Analysis of high-temperature aging and microstructure of FC LED solder joints of a silver conductive layer bonded using SAC solder

Flip-chip (FC) light-emitting diode (LED) filaments with a silver conductive layer are impeded by heat dissipation, with the flip-chip junction temperature of reaching up to 423.15 K. To overcome this problem, we simulated aging of SAC305 solder joints at a high temperature of 433.15 K. Scanning electron microscopy was performed to analyze the changes in the microstructure of the solder joints with aging time. Moreover, energy-dispersive X-ray spectroscopy was performed to analyze changes in the element content of the solder joints with aging time. The shear force of solder joints was measured using a strength tester. Results revealed that the Ag/Au content of the solder joints increased under the high-temperature conditions, resulting in the formation of cracks and holes in the solder joints. Furthermore, the reliability of the FC LED filaments was affected by the maximum shear stress that can be tolerated by the solder joints.