Bobo Yang

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.

Optical and thermal properties of flip-chip LED bulbs using chip-scale package

A kind of LED bulb which is made by the school and enterprise is introduced in this paper. Fluorescent film is used for chip-scale packaging on flip-chip LED. The film is made by spin coating method, bonded to the surface of the chip and cut off by laser and then finished by a simple process. The optical properties and thermal properties of the LED bulbs were measured by various methods. The experimental results showed that with the increasing of the voltage, color temperature and the color rendering index changing 0.522% and 0.200% respectively which can be seen as a relatively stable data. The highest surface temperature of the flip-chip LEDs using chip-scale package we estimated which can be kept between 133.8°C and 135 °C can also be accepted. These results have a certain guiding significance for the industrialization of the LED bulbs.

Study on the mechanism of color coordinate shift of LED package

In the paper, the influences of the chip, silicone and phosphors on the color coordinate shift of LED were studied. In the process of LED baking, it was found that the effect of the chip and silicone on the color coordinate drift is less than 3% through the analysis of each influencing factor. But the influence of the phosphors is large and accounted for 11.11% of the overall impact factors. Therefore, it is important to select the better green phosphors in thermal stability for the LED package and it has a guiding significance to the color coordinate of LED distribution.