Light-emitting devices having excited sulfur medium by inductively-coupled electrons

A light-emitting device having an excited sulfur medium by inductively-coupled electrons is provided. This device includes a substrate, an energy transmission coil disposed over the substrate, a transparent discharge cavity disposed over the energy transmission coil, having a substantially planar top and bottom surface, and a high-frequency oscillating power supply coupled to the energy transmission coil. While power up, the energy transmission coil induces an electromagnetic field within the transparent discharge cavity of the light-emitting device. In one embodiment, the transparent discharge cavity includes a sulfur-containing medium disposed within the transparent discharge cavity, and a buffer gas or a plurality of buffer gasses filling inner space of the transparent discharge cavity.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of Taiwan Patent Application No. 97144472, filed on Nov. 18, 2008, the entirety of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to light-emitting devices, and in particular, to light-emitting devices, wherein inductively coupled electrons excite a sulfur medium therein, and a transparent discharge chamber therein is formed with no built-in electrode inside of the chamber.

2. Description of the Related Art

There are various types of lighting sources, e.g., an incandescent lamp using radiation associated with a burning filament, a fluorescent lamp composed of an electric discharge tube and a fluorescent-powder coating for energy conversion, a high-intensity-discharge (HID) lamp that induces electrical discharge within a highly-pressurized gas or steam, and an electrodeless plasma lighting system (PLS) lamp that generates lighting plasma of gaseous media with no media-contacting electrodes.

The various types of lamps have their respective advantages. For example, incandescent lamps are excellent in color rendition and small in size. Switching circuits of the incandescent lamps are simple and low cost. However, compared to other lamps, incandescent lamps are less power efficient and have a shorter life span. In the other end, fluorescent lamps are more power efficient in emitting light and more durable than other lamps. However, while compared with incandescent lamps, fluorescent lamps are relatively large in size. Additionally, fluorescent lamps require also additional power-ballasting circuits to stabilize discharge current and light output thereof. Other gas-discharge lamps like HID lamps are also power efficient and durable. The HID lamps require, however, a relatively long time for restriking on upon switching off. In addition, HID lamps, similar to fluorescent lamps, requires additional power-ballasting circuits to assist switching. Electodeless PLS lamps possess longest life among all the above-noted lamps. The electrodeless PLS lamps though are acceptably efficient in emitting light but relatively much expensive. The electrodeless PLS lamps require also additional power-ballasting (though similar but more complex) circuits for switching.

One type of electrodeless PLS lamps, called electrodeless sulfur lamp, is particularly efficient in emitting white light of broadband spectrum even closely resembling to natural sun light.

The electrodeless sulfur lamps disclosed in the above noted US patents consist of a of golf-ball sized quartz bulb containing ten to hundred milligrams of sulfur powers and argon gas at an end of a spindle for rotation. The bulb absorbs microwave energy of 2.45 GHz generated from a magnetron to excite buffering gas of low pressure argon therein and generates gaseous discharging plasma. As a consequence, the space within the quartz bulb is thus supplied with an appropriate amount of free electrons. The sulfur powers absorb the microwave energy to heat and vaporize itself, thereby raising the pressure inside the quartz bulb to 5˜10 times that of the surrounding atmosphere. The gaseous sulfur vapors elevate to a temperature in the quartz bulb under the continuous reaction with microwaves and plasmas of inert buffering gas and are thus stimulated to ionize and discharge. The sulfur ions vigorously oscillate within the space of a narrow mean free path and collapse within itself, thereby causing a molecular-type charge/discharge process. Such a process is further aggravated by excitation and collision with highly energetic gas ions in the buffering gas plasma, thereby forming additional luminous thermal plasma of new media and emitting great amounts of photons, having a spectrum of about 73% of visible light, resembling to that of sunlight.

Nevertheless, the electrodeless sulfur lamps disclosed in the above noted US patents need a power source of more than 1.5 KW to reach a luminous efficiency of about 100 lumens per watt. As a result its application is confined to illuminate only large public spaces. In addition, the electrodeless sulfur lamps disclosed by the above noted US patents are normally large in size and appropriate means of electromagnetic shielding in most cases are mandatory, particularly for indoor applications. Therefore, the electrodeless sulfur lamps disclosed by the above noted US patents are not suitable for low power or planar luminance applications.

BRIEF SUMMARY OF THE INVENTION

Thus, a light-emitting device having an excited sulfur medium by inductively-coupled electrons is provided for low power or planar luminance applications.

An exemplary light-emitting device having an excited sulfur medium by inductively-coupled electrons comprises a substrate, an energy transmission coil disposed over the substrate, a transparent discharge cavity disposed over the energy transmission coil, having a substantially planar top and bottom surface, and a high-frequency oscillating power supply coupled to the energy transmission coil. While powering up, the energy transmission coil induces an electromagnetic field within the transparent discharge cavity of the light-emitting device. In one embodiment, the transparent discharge cavity comprises a sulfur-containing medium disposed within the transparent discharge cavity, and a buffer gas or a plurality of buffer gasses filling inner space of the transparent discharge cavity.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic diagram showing a top view of an exemplary light-emitting device100. As shown inFIG. 1, the light-emitting device100mainly comprises a substrate102, an energy transmission coil104disposed over the substrate102, a transparent discharge cavity150, and a high-frequency oscillating power supply200. An impedance matching circuit300may be optionally provided between the energy transmission coil104and the high-frequency oscillating power supply200to improve energy transmission efficiency. As shown inFIG. 1, the transparent discharge cavity150has a substantially circular shape when viewed from a top view, but configuration of the transparent discharge cavity150is not limited thereto. The transparent discharge cavity150may have other orthogonal shapes when viewed from a top view.

FIG. 2partially shows a cross section taken along line2-2of the light-emitting device100inFIG. 1. As shown inFIG. 2, the transparent discharge cavity150is a sealed hollow chamber having a substantially planar top and bottom surface. During operation, the transparent discharge cavity150may have an inner pressure of about 1-10 atm, and preferably of about 2-8 atm. The transparent discharge cavity150can be made of materials such as quartz, borosilicate, or translucent alumina which allow visible light transmission. The transparent discharge cavity150has an inner chamber154defined by a chamber wall152of a thickness of about 1-10 mm. The substrate102could be a thermally resistant substrate formed of electrical-insulating materials such as aluminum oxide or FR4 (fiber reinforced) bakelite.

The inner chamber154is filled with a buffer gas, for example, inert gases such as He, Ne, Ar, Kr, or combinations thereof, and preferably filled with a combination of at least two kinds of inert gases, such as a combination including Ar and Ne. A bottom surface of the inner chamber154may be provided with a plurality of solid sulfur mediums158. The sulfur mediums158are illustrated as being separately disposed solid ingots formed by compressing pure sulfur powders. The sulfur mediums158, however, are not limited by that illustrated inFIG. 2and may be formed as gaseous compounds comprising sulfur-containing elements such as H2S, SF4, SF6, and SO2, etc. Unlike that illustrated inFIG. 2, the sulfur mediums158of gaseous compounds may be directly filled into the inner chamber154of the transparent discharge cavity by blending with the buffer gas156beforehand.

Still referring toFIG. 2, the high-frequency oscillating power supply200(SeeFIG. 1) is coupled to two ends of the energy transmission coil104. The high-frequency oscillating power supply200can be, for example, an acoustic frequency oscillator, a radio frequency (RF) oscillator, or a microwave frequency oscillator. The energy transmission coil104may be also coupled to an impedance matching circuit300(SeeFIG. 1) which matches impedance between the high frequency oscillating power supply200and loading inferred from the energy transmission coil104. If so, the energy transmission coil104could be supplied with pulses either DC or AC pulses having a frequency of about 1 KHz˜2.45 GHz, or more preferably 5 KHz˜20 MHz by the high-frequency oscillating power supply200. Such a powering up generates an inductively coupled electric field within the transparent discharge cavity150, and thereby excites the sulfur mediums in the transparent discharge cavity150to charging/discharging process cycles which result in the emitting of light180.

Herein, during a stable operation, the light180emitted from the light-emitting device100has a broadband wavelength spectrum ranging of about 400-700 nm. The high-frequency oscillating power supply200which couples with the energy transmission coil104is operated at a power of 5-300 watts.

An embodiment of reaction mechanism of the light-emitting device100as shown inFIGS. 1 and 2is described as follows. At beginning, the energy transmission coil104provides an inductively coupled electrical field to accelerate free electrons in the transparent discharge cavity150. Such an action excites atoms of the buffer gas156which are under a lower pressure, and consequently forms a plasma of the buffer gas156and raises free electron density therein. An associated electrostatic coupling effects therein heat and vaporize the sulfur mediums158in the transparent discharge cavity150into sulfur-containing vapors. The sulfur-containing vapors increase pressure in the transparent discharge cavity150and subsequently induce another gaseous charging/discharging reaction due by frequent and vigorous collision therein. When the density of the free electrons density reaches a critical level, the electrostatic coupling effects start transforming into an electromagnetic coupling mode. Such a transition ceases using the input energy for heating up (electrostatic) the gas but instead generates an induced energy field (electromagnetic) as a vertex to accelerate and excite the sulfur atoms in the sulfur-containing vapors. As a result, it causes substantial charging/discharging process cycles of sulfur atoms and releasing even greater amounts of electrons into the plasma atmosphere.

When the sulfur-containing vapors in the transparent discharge cavity150reach a saturated pressure, the ionized buffer gases156dramatically collapse with the sulfur atoms/ions of the sulfur-containing vapors. These atoms and ions vigorously collide with each other in an increasing frequency due to an increasingly crowded particle density of narrow mean free path in between and severely thermal vibration of the particles. Such a three-body collision of atoms, ions, and electrons eventually forms charged diatomic sulfur radicals in an metastable and/or excited state. These ionization and recombination process cycles continuously increases in intensity and releases great amounts of photons which emit light180. High luminous efficacy is achieved as greater than 73% of light180is located within the visible range.

Herein, a top surface of the energy transmission coil104in the light-emitting device100illustrated inFIGS. 1 and 2is apart from a top surface150of the transparent discharge cavity150with a distance L of about 3-50 mm. The transparent discharge cavity150is formed with a greater planar size than that of the energy transmission coil104disposed over the insulative substrate120to purposely ensure energy transmission and utilization efficiency. So that the inductively coupled energy field over the top of the energy transmission coil104can be fully surrounded by the transparent discharge cavity150. Such an arrangement avoids blind-corner effects and may thus enhance efficiency of energy input for both to heat and to vaporize sulfur-containing mediums158within the transparent discharge cavity150and consequently luminous efficacy of the light-emitting device100.

FIGS. 3 and 4are schematic diagrams respectively showing two configurations of the energy transmission coil104viewed from a top view. The energy transmission coil104can be formed as a loop having a substantially rectangular helix shape or a substantially circular helix shape when viewed from a top view. However, as shown inFIGS. 5-8all from a top view, the energy transmission coil104of the light-emitting device100can be configured as other shapes that induce inductively coupling effects such as a U-shaped line (SeeFIG. 5), a meander (serpentine) line (SeeFIG. 6), a S-shaped line (SeeFIG. 7) or multiplexed parallel lines (SeeFIG. 8). The energy transmission coil104can be made of conductive metals such as copper; or sintered thick films of pastes containing conductive particles such as silver, palladium or transparent conductive oxides like ITO. Each segment in the energy transmission coil104is formed with a pitch P of about 0.1-0.5 mm therebetween and a line width W of about 0.1-10 mm. Both ends130,140of the energy transmission coil104are connected to the high-frequency oscillating power supply. Herein, the energy transmission coil104is illustrated as a conductive element disposed over the substrate102and above a top surface thereof. But it is not limited to only such a configuration. For examples, the energy transmission coil104can also be embedded within the substrate102, being directly attached on an outer surface of the chamber wall152of the transparent discharge cavity150, or be directly embedded within the chamber wall152of the transparent discharge cavity150. Such embedding alternatives may improve flatness of configurating elements and ease to integrate the light-emitting device100for particular applications such as in flat panel displays or projectors.

As shown inFIG. 9, similar to the light-emitting device100shown inFIG. 2, the light-emitting device100′ is coated with a light reflection layer170at side wall160and bottom surface162to modulate illuminating direction and to improve luminous efficacy. The light reflection layer170can be made of simple metal oxides such as titanium dioxide (TiO2) or of a multi-layered dichroic coating, which utilizes light interference, such as TiO2—SiO2to modulate light propagation. The light reflection layer170can also be made of thin metal films such as Ag, Au or Al. But for such cases, the metal films must be covered with other dielectric barriers such as glass, barium titanate, silicon oxide or titanium oxide for a proper electrical insulation from contacting the power transmission coil underneath. For all cases, the material of the light reflection layer170must be transmissive to the electromagnetic wave (e.g. a frequency between 5 KHz-20 MHz) for power transmission from the high-frequency oscillating power supply200and must be electrically insulative.

The light reflection layer170is not limited to the location illustrated inFIG. 9. As shown inFIG. 10, the light reflection layer170can be directly formed over the substrate102and fully cover the energy transmission coil104. In this case, the transparent discharge cavity150can thereby be directly disposed over the light reflection layer170. Or alternatively, the light reflection layer170can be integrated into the outer surface of the chamber wall152of the transparent discharge cavity150. And as configured inFIG. 10embedding therein the energy transmission coil104thereby omitting the necessity of the substrate102. As noted previously, the material of the light reflection layer170must be transmissive to the electromagnetic wave for power excitation from the high-frequency oscillating power supply and must be electrically insulative.

Within the transparent discharge cavity150of the light emitting device100/100′, free radicals or metastable ions of the ionized buffer gases156dramatically collapse with the sulfur atoms/ions of the sulfur-containing vapors to form charged diatomic sulfur radicals. These atoms and ions vigorously collide with each other in an increasing frequency due to an increasingly crowded particle density of narrow mean free path in between and severely thermal vibration of the particles. Such a three-body collision of atoms, ions, and electrons eventually forms charged diatomic sulfur radicals in an metastable and/or excited state. These ionization and recombination process cycles continuously increases in intensity and releases great amounts of photons which emit light180. High luminous efficacy is achieved as greater than 73% of light180is located within the visible range.

The light-emitting device100/100′ has a luminous efficiency greater than 60 lumens per watt and a color rendition that resembles sunlight. The light-emitting device100shows a wavelength distribution better match with the luminious sensitivity equivalence of human eyes than most of conventional fluorescent lamps does. Since the light-emitting device of current invention may directly emit visible white light, there is no need to coat fluorescent conversion materials on the chamber wall of the transparent discharge cavity150or to use environmentally hazardous mercury material. The light-emitting device100/100′ also shows a minimal aging characteristics over the life span thereof (usually below 5%) in color and brightness of the emitted light.

Thus, planar lighting sources with high energy efficiency may be fabricated using the light-emitting device100/100′ of the invention having high efficient luminous discharge of sulfur molecules. The light-emitting device100/100′ of the invention incorporates a planar energy transmission coil to provide inductive electrical fields for a powerful excitation. Besides, because there is no electrode built within the inner space of the transparent discharge cavity150of the light-emitting device100/100′, degradation of electrodes with plasma atmosphere is completely avoided. In addition, since the chamber is fully sealed, no chemical contaminants could be formed therein during the plasma discharging process, thereby ensuring a durable life span and reliability thereof.

The light-emitting device100/100′ of the invention is thus applicable in both applications as concentrated-type and planar-type lighting sources. For applied the light emitting device100/100′ of the invention as a planar lighting source in a backlight module, no diffusion plates or brightness enhancing films would be required as normally necessary while using conventional tubular CCFL as light-emitting source. Therefore, fabrication costs could be decreased, while increasing luminous efficacy and power utilization efficiency of the backlight module. In addition, the light-emitting device100of the invention can served as an alternative which directly emits visible light using no wavelength converting fluorescent materials as commonly adopted in conventional cold cathode fluorescent lighting (CCFL) or in flat FED displays. Therefore unfavorable effects such as poor uniformity, aging of phosphors, instability and distortion of color, and erosion of electrodes commonly observed in conventional fluorescent lighting may then be prevented. The energy input to the light-emitting device100/100′ of the invention is directly converted into visible white light with no other middle stages for adjusting wavelength.

The light-emitting device100/100′ of the invention can be further improved by adding peripheral electromagnetic shields (not shown) or other complementary components outside of the discharge cavity to enrich functionality of the light emitting device100/100′.