Mercury-free Fluorescent Lamps Research Articles

VUV photoluminescence properties of KSrPO4:Dy3+ phosphor

White-light-emitting phosphors based on phosphate host matrix, KSrPO4 doped with Dy3+, were prepared by solid state reaction and their VUV luminescent properties were firstly investigated. The excitation band peaking at 125–153 nm corresponding to the absorption of PO43− group exhibits very strong absorption. The phosphors emit warm-white luminescence under vacuum ultraviolet excitation of 147 nm, which consists of three main emission peaks located at 475, 570 and 662 nm, respectively. According to the luminescence and color chromaticity of the optimal sample KSrPO4:1 mol%Dy3+,1.3 mol%Li+, it can be a potential candidate for mercury-free fluorescent lamps.

Visible quantum cutting in Tb3+ doped BaGdF5 phosphor for plasma display panel

Visible quantum cutting (QC) via down-conversion and enhancement in photoluminescence properties has been observed in terbium (Tb3+) doped BaGdF5 phosphor. This phosphor was synthesized by varying molar concentration of Tb3+ ions via co-precipitation method. The prepared phosphor was characterized through X-ray diffraction technique. The photoluminescence spectra of BaGdF5:Tb3+ phosphor measured under vacuum ultraviolet or UV excitation. The QC process was observed in prepared phosphor due to cross relaxation and direct energy transfer between Tb3+ and Tb3+ or Tb3+ and Gd3+ ions depending on the excitation wavelength. The maximum quantum efficiencies were found to be 162, 174 and 177 %, under the excitation of 172, 187 and 240 nm respectively. The green emission of 544 nm was observed at excitation of 172 and 187 nm. Hence this phosphor may be prime candidate for application in plasma display panels and mercury free fluorescent lamps.

Optimum europium doped aluminoborates phosphors and their photoluminescence properties under VUV and UV excitation

A series of red-emitting Y1−x−yGdyEuxAl3(BO3)4 (x=0–0.15, y=0–0.25) phosphors were prepared by precipitation method. Their structure and morphology were characterized by XRD and SEM, and their photoluminescent properties under VUV and UV excitation were investigated. The results indicate that the phosphors are suitable to the excitation at VUV light of 147 nm and UV light of 254 nm. A set of the optimized process parameters (the calcination temperature at 1000 °C, 10 mol% Eu3+ and 20 mol% Gd3+ doping concentrations) can help the phosphors to improve their luminescent properties. Therefore, the optimized process parameters enable Y1−x−yGdyEuxAl3(BO3)4 (x=0–0.15, y=0–0.25) phosphors to have great potential to be used in PDP and mercury-free fluorescent lamp in the future.

Fluorescence properties of SrAl12O19 : Pr3+ quantum cutting phosphor

A phosphor, SrAl12O19 doped with Pr (SA : Pr), is investigated in this research in order to improve the luminous efficacy of a mercury-free Xe discharge fluorescent lamp (FL). The obtained sample works as a quantum cutting phosphor which converts an absorbed photon of Xe emission at 172 nm into two visible photons, one at 401.8 nm and the other at 486.3, 526.3, 623.7 or 644.6 nm. The concentration of Pr is optimized and the visible emission of the phosphor becomes maximum at 5 mol%. The photoluminescence measurements show that the relative quantum efficiency of SA : Pr (Pr: 5 mol%) is 38.4% of BaMgAl10O17 : Eu2+ (BAM : Eu). The luminance of a Xe dielectric-barrier-discharge (DBD) FL coated with SA : Pr (Pr: 5 mol%) achieves 28.8% of the same lamp with BAM : Eu. The CIE colour coordinate of the SA : Pr (Pr: 5 mol%) excited by the Xe-DBD lamp is x = 0.307 and y = 0.292. The SA : Pr phosphor has an excitation band peaking at 468 nm corresponding to the 1I6 state and a low intensity excitation band lying from 250 to 420 nm. The latter is attributed to the self-trapped exciton (STE) band. This STE band causes an energy path due to non-radiative transition from 1S0 to 3P0 in the excitation at 172 nm. The former excitation band around 468 nm coincides with an ordinary blue LED's emission. When the phosphor is excited at this wavelength, the emission spectra are observed at 486.3, 526.3, 623.7 and 644.6 nm. Therefore, the SA : Pr may alternatively be useful for white LEDs excited by blue light.

Enhanced blue luminescence in BaMgAl10O17:Eu, Er, Nd nanophosphor for PDPs and Mercury free fluorescent lamps

The Er3+/Nd3+ codoped BaMgAl10O17:Eu2+ phosphor nanoparticles have been synthesized through solution combustion method. Nanophosphor has shown intense broad blue photoluminescence (PL), corresponding to the 4f65d→4f7 electronic transition of Eu2+ ion under vacuum ultraviolet (147nm) as well as UV (355nm) excitations. An enhancement in blue emission of Eu2+ has been observed on the codoping of Er3+/Nd3+ ions and concentration of the doping ions have been optimized. Lifetime of the 4f65d→4f7 transition has been measured and discussed. The enhancement in emission intensity of codoped blue nanophosphor is explained by energy transfer from the Er3+/Nd3+ ions and created defect states to the Eu2+ in the BaMgAl10O17. This phosphor has also shown better emission intensity as compared to commercial blue phosphor under VUV excitation and thus making it attractive for the application in plasma display panels and mercury free-fluorescent lamps.

Discharge characteristics of mercury-free flat fluorescent lamps with various electrode configurations analysed through a two-dimensional fluid model simulation

The discharge characteristics and factors related to the luminous efficacy of mercury-free flat fluorescent lamps (MFFLs) with three different types of coplanar, counter and combination electrode configurations were studied via a two-dimensional numerical simulation. The spatiotemporal distributions of the potential, electric field, electron density, Xe** density and current waveforms of the MFFLs were obtained and analysed. The MFFL with the combination electrode configuration shows the highest vacuum ultraviolet (VUV) efficacy value. The vertical electrode in the MFFL with the combination electrode configuration prevents the electric field at the gap space from decreasing rapidly, and extends the discharge path. The effects of the vertical electrode help one to increase the Xe excitation efficacy. In addition, a new auxiliary electrode was proposed in the original MFFL with the combination electrode configuration. The MFFL with the new auxiliary electrode has broader distributions of electrons and Xe** species, and a higher VUV efficacy value than the original MFFL with the combination electrode configuration at the same voltage.

Preparation and Photoluminescence of Nano-Sized Green Phosphors by Solution Combustion Synthesis

By adopting a facile solution combustion synthesis (SCS) method, pure well-crystallized (Ba,Sr)MgAl10O17:Mn green phosphors were successfully prepared. The crystallinity, particle size, morphology, and luminescent properties were characterized by XRD, FE-SEM and spectrofluorometer respectively. The results indicated that the obtained phosphors have spherical morphology, good crystallinity, and strong green emission. The emission spectra of obtained nanophosphor on 147nm excitation consist of a wide band with the peak at 518nm, which corresponds to the transition from the 3d5(4T1g) excited state to the 3d5(6A1g) ground state of Mn2+. The synthesized phosphors can be efficiently excited at VUV light and have potential application in Plasma Display Panels (PDPs), 3D displays and mercury-free fluorescent lamps

Investigation and application of quantitative relationship between sp energy levels of Bi3+ ion and host lattice

Information on 1S0-3P1 (A band) and 1S0-1P1 (C band) transition energy of Bi3+ ion in dozens of different compounds has been gathered and analyzed. With the use of the dielectric theory of the chemical bond for complex crystals, relationships between A and C absorption band and environmental factor he were established: EA=2.972+6.206exp (−he/0.551); EC=3.236+10.924exp (−he/0.644). For Bi3+ doped hosts with known structure and refractive index, it is possible to predict Bi3+ energy level position with an good accuracy of typically ±0.51eV using the two relationships. Moreover, a direct relationship between A and C band was deduced: EC=3.236+2.290(EA−2.972)0.856. Thus a very simple method to predict C band position was proposed. This work will be of great help to understand spectroscopy of Bi3+ and will be useful for developing new PDP, LED and mercury-free fluorescent lamp phosphors.

The Effects of Electrode Configuration on the Luminance and Luminous Efficacy of Mercury-Free Flat Fluorescent Lamp

To obtain highly efficient and stable discharges in mercury-free flat fluorescent lamps (MFFLs), the effects of the main electrode configuration on the electro-optical characteristics such as the operating voltage margin, luminance, and luminous efficacy are investigated. The spatiotemporal characteristic of the infrared emission from discharges in different electrode configurations (conventional coplanar, counter, and combination discharges) is also studied with an intensified charge-coupled device camera to see the differences with the electrode configuration variation. The MFFL having the combination electrode configuration with Ne-30% Xe gas mixture and a total pressure of 13.3 kPa showed high luminance from 3102 to 22 067 cd/m2 and high luminous efficacy from 49 to 93.5 lm/W for the warm white daylight with a color coordinate of (0.36, 0.36).

BaAl 12O 19:Mn 2+ green emitting nanophosphor for PDP application synthesized by solution combustion method and its Vacuum Ultra-Violet Photoluminescence Characteristics

Nanostructured BaAl 12O 19:Mn 2+ phosphor particles of nano-rod morphology with diameter 40–100 nm and length up to 200–600 nm has been synthesized by solution combustion method and its photoluminescence characteristics have been studied by Vacuum Ultra-Violet Photoluminescence spectrometer (VUVPL) under 147 nm excitation. The crystallographic phase purity of BaAl 12O 19:Mn 2+ nanostructured phosphor particle synthesized by solution combustion approach is confirmed by X-ray diffraction (XRD). The broadening of XRD diffraction peaks indicates nanocrystalline nature of particles present in powder. The emission spectrum of BaAl 12O 19:Mn 2+ nanophosphor on 147 nm excitation consists of a wide green band with a peak at about 515 nm, which is due to a 3d 5 ( 4T 1g)–3d 5 ( 6A 1g) transition corresponds of Mn 2+ ions. It is found that the concentration quenching is obtained when Mn 2+ content ( x) is 0.05 in BaAl 12O 19: xMn 2+ nanophosphor on 147 nm excitation. The decay time of 3d 5 ( 4T 1 g)–3d 5 ( 6A 1 g) transition of Mn 2+ ions at 147 nm excitation is about 23 ms for BaAl 12O 19:Mn 2+ nanophosphor. This nanostructured green emitting BaAl 12O 19:Mn 2+ phosphor can find potential application in Plasma Display Panels (PDPs) and mercury-free fluorescent lamps.

High‐luminance and luminous‐efficacy mercury‐free flat fluorescent lamp (MFFL) with local‐dimming functionality

Abstract— In order to realize high‐luminance and luminous‐efficacy mercury‐free flat fluorescent lamps (MFFLs) for LCD backlighting, the phosphor profile was optimized to enlarge the surface area. The proposed uneven profile of the rear phosphor increases the effective surface area of the phosphor, resulting in a wide luminance range from 3000 to 16,788 cd/m2 with a corresponding high luminous efficacy from 66 to 34.7 lm/W, respectively. Also, a dynamic operation method for an adaptive local‐dimming and scanning operation is proposed which can be used in a 32‐in. multi‐structured configuration having one inverter system. With the deployment of the bipolar drive scheme and dual auxiliary electrodes, a stable and selective diffuse glow discharge with high luminance is possible.

The Effects of Electrons on the Electro-Optical Characteristics of Mercury-Free Flat Fluorescent Lamps

New mercury-free Flat Fluorescent Lamps (FFLs) with a different kind of phosphor layers were fabricated in order to investigate the effects of electrons with the surplus energy on the electro-optical characteristics. Discharge characteristics of the FFLs were compared as functions of the gas pressure and the mixture ratios, and with or without phosphor layer on the front plate. The experimental results revealed that FFLs with the PL (Photoluminescence) phosphor layer on the front and the rear plates show the highest luminance. However, it is found that the difference of luminance between FFLs with the CL (Cathodoluminescence) phosphor layer and FFLs with the PL phosphor on the front plate is considerably decreased in the cases of the gas pressure below 50 Torr and the discharge cell with a cell depth of 0.8 mm, indicating that the electrons play a role in the excitation of the phosphor under a certain discharging condition.

Improvement of Luminance and Luminous Efficacy of Mercury-Free, Flat Fluorescent Lamp by Optimizing Phosphor Profile

A highly efficient mercury-free fluorescent lamp (MFFL) was developed for an alternative to fluorescent lamps containing mercury. The lamp has a simple structure with two main electrodes running parallel to each other and an auxiliary electrode. In order to improve the luminance and luminous efficacy of MFFLs further, we optimized the thickness of rear and front phosphors on the inner surfaces of the lamp, and then adopted an uneven distribution profile for the rear phosphor to increase the surface area of the phosphor. The MFFL with the optimized phosphor profile showed a wide luminance range from 3315 to 17133 cd/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with the corresponding luminous efficacy from 75.2 to 42.5 lm/W with the color coordinate around (0.32, 0.32) for daylight.

Influence of Xe Gas Concentration on Plasma Parameters and Luminance Characteristics in Fluorescent Lamps driven by an Inductively Coupled Radio Frequency Discharge Using Ne/Xe Mixture Gases

A mercury-free and electrodeless discharge fluorescent lamp is expected for preserving the environment and a long lifetime. Influence of Xe gas concentration on plasma parameters such as density and temperature of electrons and luminance characteristics is investigated in a fluorescent lamp driven by inductively coupled radio frequency discharge using Ne / Xe mixture gases. It is found that the electron density has a peak value for a Xe gas concentration of 1 % and then decreases with increasing the Xe gas flow rate, whereas the electron temperature takes a minimum value for the Xe gas concentration of 1 % and then increases with increasing the Xe gas concentration. The luminance of the fluorescent lamp decreases remarkably with increasing Xe gas concentration up to 1% and then gradually decreases. The color of the fluorescent lamp changes from red to purple when the Xe gas concentration increases.

Luminescence properties of NaGd(PO3)4:Eu3+ and energy transfer from Gd3+ to Eu3+

The luminescence properties of polyphosphates NaEu x Gd(1−x)(PO3)4 (x = 0–1.00) and the energy transfer from Gd3+ to Eu3+ were studied. In undoped NaGd(PO3)4 sample, the photon cascade emission of Gd3+ was observed under 8S7/2 → 6GJ excitation (201 nm) in which the emission of a red photon due to 6GJ → 6PJ transition is followed by an ultraviolet photon emission due to 6PJ → 8S7/2 transition. When part of Gd3+ ions in the host NaGd(PO3)4 were substituted by Eu3+ ions, the NaGd(PO3)4:Eu3+ sample showed intensive red emission under 172-nm vacuum-ultraviolet (VUV) excitation which is suitable for mercury-free fluorescent lamps and plasma display panel applications. Based on the VUV–visible spectroscopic characteristics and the luminescence decay properties of NaGd(PO3)4:Eu3+, it was found that the quantum cutting by a two-step energy transfer from Gd3+ to Eu3+ can improve the red emission of Eu3+ ions under VUV excitation but only a part of the excitation energy in the excited 6PJ states within Gd3+ ions can be transferred to Eu3+ ions for its red emission, and the nonradiative energy transfer efficiencies from the excited 6PJ states within Gd3+ to Eu3+ were calculated.

Recent Developments in the Field of Inorganic Phosphors

Because fossil fuels are becoming scarce and because of the expected climate change, our standard of living can only be maintained by a significant increase in energy efficiency. Large amounts of energy are consumed for lighting and during operation of displays. Thus, the targets are the development of economical light sources like white-light-emitting diodes and display panels with enhanced efficiency. Solar energy is converted into electricity by solar cells, and their efficiency must be improved considerably. A possible contribution might be delivered by phosphors which allow the conversion of thermal radiation into electrical energy. Although the target of energy efficiency is very important, we must not overlook that medical imaging diagnostic methods require efficient and sensitive detectors. For the solution of these central questions, inorganic solid-state materials doped with rare-earth ions are very promising and are therefore in the focus of current research activities.

Polarization selection rules and optical transitions in terbium activated yttrium tantalate phosphor under x-ray, vacuum-ultraviolet, and ultraviolet excitations

The terbium-activated yttrium tantalite (YTaO(4):Tb(3+)) phosphor is of great interest due to the interesting spectroscopic properties of rare earth ions in crystals and also practical use in x-ray imaging. Using the group-theoretical approach, we analyze the selection rules for the transition between Stark components of Tb(3+) in symmetry of the actual crystal field and the polarization for the allowed transitions. The luminescence upon UV, vacuum-ultraviolet (VUV), and x-ray excitation is presented and discussed. The YTaO(4):Tb(3+) phosphors are found to be efficient VUV-excited luminescent materials that could be used not only in x-ray intensifying screens, but also in mercury-free fluorescent lamps or plasma display panels.

Three-Dimensional Simulations of Patterned Electrodes in Mercury-Free Flat Fluorescent Lamps

The effect of patterned electrodes in Hg-free flat fluorescent lamps is investigated by using 3-D fluid simulations. The visualization of Xe*( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> p <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ) density profiles is important to observe the efficiency dependence on the 3-D electrode shapes. The luminous efficiency of the patterned-electrode models increases about 20% as compared with that of the reference model because of the reduction of power consumption.

Vacuum ultraviolet excited photoluminescence properties of Gd 2O 2CO 3:Eu 3+ phosphor

The Gd 2O 2CO 3:Eu 3+ with type-II structure phosphor was successfully synthesized via flux method at 400 °C and their photoluminescence properties in vacuum ultraviolet (VUV) region were examined. The broad and strong excitation bands in the range of 153–205 nm owing to the CO 3 2– host absorption and charge transfer (CT) of Gd 3+-O 2– were observed for Gd 2O 2CO 3:Eu 3+. Under 172 nm excitation, Gd 2O 2CO 3:Eu 3+ exhibited strong red emission with good color purity, indicating Eu 3+ ions located at low symmetry sites and the chromaticity coordination of luminescence for Gd 2O 2CO 3:Eu 3+ was ( x=0.652, y=0.345). The photoluminescence quenching concentration of Eu 3+ excited by 172 nm for Gd 2O 2CO 3:Eu 3+ was about 5%. Gd 2O 2CO 3:Eu 3+ would be a potential VUV-excited red phosphor applied in mercury-free fluorescent lamps.

Tungsten coatings by chemical solution deposition for ceramic electrodes in fluorescent tubes

In the lighting industry, the concept of ceramic cold cathodes provided with an inside tungsten coating is under consideration to be applied in mercury-free fluorescent lamps for advertising purposes. In this regard, the applicability of chemical solution deposition to fabricate metallic films on the inner surface of alumina tubules was established. The technique involves the preparation of tungsten oxide layers from a peroxotungstic acid precursor solution and their subsequent reduction to tungsten in the presence of hydrogen. Diverse characterisation of the precursor and the intermediates was carried out in order to determine the influence of their properties on the quality of the final coatings. By acquiring the optimum process parameters, highly-conducting tungsten films were obtained. The temperatures allowing for conversion of the oxide to the metal as well as for sintering of the derived tungsten films were observed to be substantially lower than in bulk processes. Electrode prototypes of the described type were accordingly realised and operated successfully in a fluorescent tube test setup, thus proving the feasibility of the hitherto theoretical idea.