Field Emission Lamps Research Articles

White Cathodoluminescence Emission from Eu‐Doped SiAlON Thin Films

SiAlON materials in thin film configuration are very attractive because their composition can be easily modified from that of silicon dioxide to that of silicon nitride to effectively tune their electrical and optical response, therefore making them suitable for a wide range of optoelectronic devices. In addition, rare‐earth doped SiAlON phosphors in powder configuration are excellent down‐converters to visible light when excited by ultraviolet‐blue photons from light emitting diodes. In this work, the direct excitation by electrons of amorphous nanostructured Eu‐doped SiAlON thin films is explored. XPS analysis shows that the Eu in the films is in its divalent oxidation state (Eu2+), with traces of Eu with a richer oxygen coordination at the film surface. The cathodoluminescence emission from the films is dominated by a wide emission band (FWHM 195 nm) in the visible associated with the Eu2+ 5d to 4f electronic transitions, with a small narrow peak contribution from Eu3+ intra‐4f electronic transitions. Assessment of the CIE color coordinates shows that the spectral emission is close to the pure white. These results show the excellent potential of the Eu‐doped SiAlON films for its implementation in CMOS structures as white light solid state emitters in field emission lamps and displays.

Enhanced Efficiency of Field Emission Lamps with Carbon Nanotube Cold Cathode and Beam Uniformity Enhancement Electrode (BEE)

Enhanced Efficiency of Field Emission Lamps with Carbon Nanotube Cold Cathode and Beam Uniformity Enhancement Electrode (BEE)

Nitride phosphors as robust emissive materials in white flat field emission lamps

Nitride phosphors, showing very promising photoluminescence properties, are now attracting great attention as down-conversion luminescent materials in white light emitting diodes (wLEDs). Their interesting cathodoluminescence properties, such as high stability and reliability against electron bombardment, also enable them to be used in white flat field emission lamps (FELs). Dual-band white FELs were prepared by using blue AlN:Eu2+ and yellow Ca-α-sialon:Eu2+ in this work. These FELs show no luminance saturation and stable chromatic coordinates with increasing anode voltage and current. Driven at 7 kV and 100 μA, the white FEL with the AlN:Eu2+ to Ca-α-sialon:Eu2+ ratio of 0.65 to 0.35 has the luminance of 3,412 cd/m2, a color temperature of 3,430 K, and a color rendering index of 76. Higher color rendition of 93-95 can be obtained by using the phosphor blend of AlN:Eu2+, β-sialon:Eu2+ (green) and CaAlSiN3:Eu2+ (red). It indicates that nitride phosphors could be used as robust emissive materials in highly reliable white FELs.

Helical-Cathode Bulb-Shaped Field Emission Lamps Using Carbon Nanocoil Electron Emitters.

Bulb-shaped field emission lamps (FELs) with a helical cathode filament were simulated and fabricated in this research. The light bulbs comprised a helical stainless steel filament cathode grown with carbon nano-coils (CNCs) and an Al anode deposited on the bottom hemisphere of a 60-mm-diameter glass bulb. White light was generated when the field-emitted electrons bombarded a layer of three-color phosphor coated on the anode. A numerical simulation model for the helical-cathode FELs was constructed, and the field emission (FE) performance was carefully studied. Due to the screening effect, the electric field strength as well as the FE current density on the inner side of the helix dramatically decreased with decreasing helical pitch. Real FELs using cathodes with various helical radii and pitches were fabricated and their FE currents were measured. The theoretical and experimental results were in good agreement. A maximum total FE current was found at a pitch of 16 mm (helical radius = 2 mm), where the optimum trade-off between a large total surface area and a small screening effect was obtained. The optimized FEL showed a total luminous flux of about 220 lm at an applied voltage of 8 kV and a color rendering index of 94. Compared to a straight filament cathode, a helical cathode offered a higher total FE current or, alternatively, a lower current density and a longer cathode life, if we fix the total current by using a lower voltage.

Carbon nanotube sheets used in field-emission lamps with vacuum-sealed diode structures

ABSTRACTWe applied carbon nanotube (CNT) sheets, which are high-purity and suitable for mass production, to field-emission lamps (FELs) with vacuum-sealed diode structures. Three such FELs were designed and fabricated to correspond to the field-emission characteristics of individual CNT sheets. We suppressed the variation in the anode–cathode voltage to within the range of 5.4–6.0 kV, which contributes to the light output of the FELs. The stabilities of the FELs ranged from −0.65% to 0.26% in the short term; therefore, we confirmed that the high-purity CNT sheets were stable during operation. All FELs could be operated for 500 h without significant degradation, even when the FEL was operated in a passive vacuum instead of a dynamic vacuum.

Field Emission Lamps Prepared with Dip-Coated and Nickel Electroless Plated Carbon Nanotube Cathodes.

Fabrication and efficiency enhancement of tubal field emission lamps (FELs) using multi-walled carbon nanotubes (MWNTs) as the cathode field emitters were studied. The cathode filaments were prepared by eletrolessly plating a nickel (Ni) film on the cathode made of a 304 stainless steel wire dip-coated with MWNTs. The 304 wire was dip-coated with MWNTs and nano-sized Pd catalyst in a solution, and then eletrolessly plated with Ni to form an MWNT-embedded composite film. The MWNTs embedded in Ni not only had better adhesion but also exhibited a higher FE threshold voltage, which is beneficial to our FEL system and can increase the luminous efficiency of the anode phosphor. Our results show that the FE cathode prepared by dipping three times in a solution containing 400 ppm Pd nano-catalysts and 0.2 wt.% MWNTs and then eletrolessly plating a Ni film at a deposition temperature of 60 °C, pH value of 5, and deposition time of 7 min has the best FE uniformity and efficiency. Its emission current can stay as low as 2.5 mA at a high applied voltage of 7 kV, which conforms to the high-voltage-and-low-current requirement of the P22 phosphor and can therefore maximize the luminous efficiency of our FEL. We found that the MWNT cathodes prepared by this approach are suitable for making high-efficiency FELs.

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

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.

Improvement of field-emission-lamp characteristics using nitrogen-doped carbon nanocoils

Carbon nanocoils (CNCs) synthesized using thermal pyrolysis chemical vapor deposition on 304 stainless steel wire substrates were used as the cathodes of field emission lamps (FELs). The effects of the growth temperature on the FE performances were studied, and we observed that uniform and dense CNCs that are suitable for use as FE cathodes can be synthesized at 600°C. We also found that a nitrogen doping post-treatment can significantly improve the FE efficiency of the CNCs. When doped at 200°C with a nitrogen flow rate of 500sccm for 30min, the nitrogen content of the CNC surface could reach 4.9wt.%. ESCA analysis indicates that the doped nitrogen atoms formed CNx bonding and increased the sp2 clusters in the CNCs. The turn-on voltage was reduced from 2.1V/μm to 1.4V/μm, and the β value increased considerably from 2465 to 3241 after N-doping post-treatment. The bulb-type FELs using our N-doped CNC cathodes showed a good luminous efficiency as high as 75lm/W at 8kV.

Stable field emission lamps based on well-aligned BaO nanowires

Well-aligned BaO nanowires were synthesized on ITO glass substrates by a hydrothermal process. The morphology and composition of the BaO nanowires were characterized by field emission scanning electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction, X-ray diffraction, and energy dispersive X-ray spectroscopy. The results confirmed that BaO nanowires had single crystalline cubic structures and grew along the [111] direction. The well-aligned BaO nanowires show superior field emission properties, and exhibited a low turn-on field (∼0.9 V μm−1), a low threshold field (∼3.59 V μm−1), a high field enhancement factor (β = 2463), and a good stability of the emission current. The field emission lamps fabricated by using the BaO nanowires as emitters display uniform and bright emission patterns under the diode mode. These results demonstrate that such BaO nanowires are promising for application in practical flat panel displays.

Long lifetime emission from screen printing carbon nanotubes over 45,000 h at 1.27 mA/cm2 with 10% duty ratio

A long time operation of field electron emission over 45,000h was achieved using the screen printing carbon nanotube (CNT) emitter fabricated on an ITO coated glass substrate. The measurement was carried out in an ultra-high vacuum chamber at around 3×10−7Pa in pressure with continuously applying voltage of rectangular pulses at 743V or 730V peak, 60Hz frequency and 10% duty ratio. The emission current corresponding to the voltage pulse at 1.27mA/cm2 density was repeatedly and reproducibly observed for more than 5years. Because the operated condition was 10 times higher at the current density than that of the conventionally developed field emission lamps (FELs), the expected lifetime of the presented emitter will be 450,000h though the vacuum level of the measurement was extremely higher than that of the actual operation of FELs. By investigating the morphology of the emitter after terminating the operation, it was found that sparse bundles of agglomerated CNTs were standing in the long lifetime CNT emitter.

Bulb-Shaped Field Emission Lamps Using Carbon Nano-Coil Cathodes

Bulb-shaped field emission lamps (FELs) using carbon nano-coil (CNC) cathodes were fabricated and their performances were characterized. A straight steel wire grown with CNCs was placed on the symmetry axis in the bulb as the cathode. The anode was defined by a Ni film deposited on the bottom hemisphere of a 60-mm-diameter glass bulb. And a phosphor layer was coated on the Ni film for light generation via cathodoluminescence. A numerical simulation model for this geometry also was constructed. The simulated current-voltage curves agree well with the experimental results and reproduce the trends observed in the experiment. The effects of varying the length and diameter of the cathode were studied. Both experiment and simulation showed that the total field emission current increases with the cathode length and decreases with the cathode diameter. Although the design is simple and inherently low-cost, good uniformity of light emission over the entire anode was demonstrated.

63.1: Invited Paper: Sharp, Uniform, Stable, and Environment‐hard Transfer‐Mold Field‐Emitter Arrays

AbstractSharp, uniform, stable, and environment‐hard field‐emitter arrays (FEAs) have been fabricated by Transfer‐Mold fabrication method. These FEAs have potential for realizing stable and low operation voltage field‐emission displays and field‐emission lamps that are resistant to highly oxidizing atmospheres during the fabrication process.The extremely sharp and uniform Transfer‐Mold FEAs, which have the average tip radius of 2.6‐3.5 nm, have been developed by using the Transfer‐Mold fabrication method. These tip shapes including height are extremely uniform being different from CNTs' nonuniform tip radii, height and pitch. Also, these tip radii are similar to the diameter of the singlewalled CNTs, 0.4–6 nm, or less than the diameter of the multiwalled CNTs, 5–10 nm. The low operation voltage Transfer‐Mold FEAs has turn‐on fields of 17.5–21.8 V/μm at the short distance between anode and emitter, less than 30 μm. However, other conventional FEAs such as Spindt‐type FEAs, Gray‐type FEAs and CNTs FEAs have the approximated turn‐on fields of 50–600 V/μm. Therefore, those values of the turn‐on voltages are lower than those of other conventional FEAs and can be applicable for vacuum nanoelectronic devices such as FEDs and FELs. The current fluctuations of FEAs without resistive layer are the lowest value ever reported, ±1.6%, compared with 5‐several hundred % of the conventional FEAs. Also, the Transfer‐Mold Mo FEAs having the base lengths of 36–1570 nm without resistive layer, exhibited extremely stable current fluctuations of as low as ±1.6‐3.3% due to the extremely uniform geometric factors. Moreover, those of the environment‐hard Transfer‐Mold FEAs even under the oxygen radical or plasma treatments are as low as ±5.0–7.5%. However, for conventional FEAs with and without resistive layers, those are usually 5–100% and more than 100%, respectively. Therefore, the extremely sharp, uniform, stable, and environment‐hard Transfer‐Mold FEAs are useful for the stable and reliable vacuum nanodevices such as FEDs and FELs to a great extent.

Very High Field Emission from a Carbon Nanotube Array With Isolated Subregions and Balanced Resistances

Field-emission electron sources can be used in microwave amplifiers, microthrusters, field-emission lamps, and X-ray tubes. However, both large cathode areas (multiple square millimeters) and large total currents ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&gt;$</tex></formula> 10 mA) are required in these devices. It has been reported that the average field-emission current density can be very high when the emission area is quite small. However, the current density decreases a lot when the emission area is large. The nonuniform field emission from a large field emitter array and its influences on the total emission current are analyzed in this paper. From the results of the numerical simulations, the relations between the average field-emission current density and the size of the carbon nanotube (CNT) array are found. Due to the standard height deviation of CNTs in an array, some CNTs may be quite high if the array is large. To avoid the current overload from the highest CNT, the total field-emission current has a nonlinear relation with the area of the CNT array. Therefore, the field-emission current is limited even if the emission area is large. According to the results of the theoretical studies, a new way is proposed to enhance the field-emission current. In this method, the field emitter array is divided into a few isolated subregions. After the measurement of the field-emission characteristics of different isolated subregions, the balanced resistances are attached to these regions to improve emission uniformity. Finally, the field-emission current increases from 5 to 13.8 mA after the adoption of isolated subregions and balanced resistances, and the average current density is 1.76 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{A/cm}^{2}$</tex></formula> .

Field-emission lamps (FELs) containing carbon nanomaterials to replace conventional fluorescent lamps

Field-emission lamps (FELs) containing carbon nanomaterials to replace conventional fluorescent lamps

Ion-beam morphological conditioning of carbon field emission cathode surfaces

Samples of reticulated vitreous carbon (RVC) and paste graphite film have been evaluated for field-emission properties both before and after surface modification. The RVC has been treated using an open-air laser method. The graphite has been treated using an Ar-ion flood bombardment method. Both methods result in a change in surface morphology of the emission cathode which physically resembles results obtained using current or voltage stress treatment methods. Emission properties become more uniform, exhibit less noise, and, in the best cases, match results seen from carbon nanotubes or ultra-nanocrystalline diamond cathodes. The results demonstrate a method for obtaining large total currents at optimal extraction voltages, from large-area, low-cost cathodes. This method is useful for applications, such as field-emission lamps and x-ray tubes, which do not require nanofabricated, lithographically-patterned cathode structures.

FIELD EMISSION FROM NANOSTRUCTURE CARBON FILMS

We studied the field emission properties of carbon nanostructure, which comprised of high density carbon nanotips on Si. These carbon nanotips are grown on metal coated Si by a high density plasma chemical vapor deposition (HDPCVD) using an inductively coupled plasma. The emission current increases with increasing the growth temperature. They exhibited an emission current density of 1 mA/cm 2 at a field of 1.95 V /μ m when the growth temperature was 700°C. We developed high brightness field emission lamps using the carbon nanotips.

Flat-panel field-emission lamps for the illumination of liquid-crystal displays and field-emission displays based on diamond-coated silicon points

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text E. I. Givargizov, "Flat-panel field-emission lamps for the illumination of liquid-crystal displays and field-emission displays based on diamond-coated silicon points," J. Opt. Technol. 66, 525- (1999) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article