Improvement of Lighting Uniformity and Phosphor Life in Field Emission Lamps Using Carbon Nanocoils

Kun-Ju Chung,Ming-Der Ger,Yih-Ming Liu,Meng-Jey Youh,Wen-Ko Huang,Nen-Wen Pu

doi:10.1155/2015/373549

Kun-Ju Chung, Ming-Der Ger + Show 4 more

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https://doi.org/10.1155/2015/373549

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Abstract

The lighting performances and phosphor degradation in field emission lamps (FELs) with two different kinds of cathode materials—multiwalled carbon nanotubes (MWCNTs) and carbon nanocoils (CNCs)—were compared. The MWCNTs and CNCs were selectively synthesized on 304 stainless steel wire substrates dip-coated with nanosized Pd catalysts by controlling the growth temperature in thermal chemical vapor deposition, and the film uniformity can be optimized by adjusting the growth time. FELs were successfully fabricated by assembling these cathode filaments with a glass bulb-type anode. The FEL with the CNC cathode showed much higher lighting uniformity and light-spot density and a lower current at the same voltage than that with the MWCNT cathode filament, and its best luminous efficiency was as high as 75 lm/W at 8 kV. We also found that, for P22, the phosphor degradation can be effectively suppressed by replacing MWCNTs with CNCs in the cathode, due to the much larger total bright spot area and hence much lower current density loading on the anode.

Highlights

The phenomenon of field emission (FE) was proposed by Fowler and Nordheim in 1928 [1]
In accordance with Pan’s study, our study showed that the carbon nanocoils (CNCs) cathode field emission lamps (FELs) was brighter than the Carbon nanotubes (CNTs) one and had excellent lighting-spot density and uniformity, which can be attributed to the numerous emission sites on the single CNC, as opposed to the only one emission site at the tip of a multiwalled CNTs (MWCNTs)
For P22, the phosphor life estimated from the current density can reach about 810 h for the CNC cathode FEL, while for the MWCNT cathode FEL it is only about 115 h

Summary

Introduction

The phenomenon of field emission (FE) was proposed by Fowler and Nordheim in 1928 [1]. FEL devices have numerous advantages such as short switching times, low power consumption, high brightness, and low heat generation. The bulb they made can achieve an emission current density as high as 300 mA/cm and a luminous efficiency of 26.4 lm/W Compared to those commonly used lamps such as CCFLs, these CNT-FELs have not shown significantly higher luminous efficiency or brightness. The emission from a carbon nanocoil occurs at its tip, and on its top surface, where the electric field is concentrated [25] These results indicated that CNCs are a great potential material for FEL cathodes. Higher lighting uniformity and light-spot density at lower current density, as well as greater luminescence efficiency and a longer anode phosphor life, were observed in the FEL with a CNC cathode

Experimental

Results and Discussion

Conclusions