Halophosphate Phosphors Research Articles

Structural and Photoluminescence Characterization of Oxyfluorides for Phosphor Applications

ConspectusRare-earth-containing phosphors were crucial to the advances made to compact fluorescent lamps (CFLs), which assisted in protecting a widely used halophosphate phosphor from degrading after exposure to a high ultraviolet flux. The CFL phosphors are often coated twice by depositing a light coat of rare-earth-containing phosphors over the inexpensive halophosphate phosphor, which generates white light with high efficacy and a good color rendering index and possesses a balance between phosphor cost and performance. Costs of phosphors can be mitigated by requiring lower rare-earth ion concentrations or by completely eliminating rare-earth ions, which was one of the main goals of investigating the oxyfluorides Sr3AlO4F and Ba2SrGaO4F as potential phosphors. Changes in the Sr3AlO4F and Ba2SrGaO4F structures were studied using high-resolution neutron diffraction annealing these materials in 5%H2/95%Ar and 4%H2/96% Ar, respectively. Annealing in these atmospheres causes self-activated photoluminescence (PL) to occur under 254 nm light, which makes them ideal materials for rare-earth-free CFL phosphors. Additionally, these hosts possess two distinct sites for isovalent or aliovalent substitution of Sr denoted as the A(1) and A(2) sites. Ga3+ can be substituted for Al3+ at the M site, which is known to have an impact on the self-activated PL emission color. The structural distortions noted included closer packing in the FSr6 octahedrons and AlO4 tetrahedrons in the Sr3AlO4F structure as compared to in air-annealed samples, which show no PL emission. Temperature-dependent studies reveal that both the air- and reductively annealed samples have identical thermal expansion within this temperature range (3-350 K). High-resolution neutron diffraction at room temperature confirmed the tetragonal structure (I4/mcm) for Ba2SrGaO4F, a novel material in the Sr3AlO4F family of materials, has been synthesized via a solid-state method. Analysis of the refined Ba2SrGaO4F structure at room temperature revealed expansion in the lattice parameters and its polyhedral subunits between the reductively annealed and air-annealed samples, which are correlated with the PL emission. Previous studies related to the application of these host structure types revealed that they have potential as commercial solid-state lighting phosphors due to their ability to resist thermal quenching as well as accommodate various levels of substitutions that will assist with color tunability.

Reliability of Blue-Emitting Eu2+-Doped Phosphors for Laser-Lighting Applications.

This paper investigates the reliability of blue-emitting phosphors for Near-UV (NUV) laser excitation. By means of a series of thermal stress experiments, and of stress under high levels of optical excitation, we have been able to identify the physical process responsible for the degradation of Eu2+-activated alkaline-earth halophosphate phosphors under typical and extreme operating conditions. In particular, for temperatures equal to or greater than 450 °C the material exhibited a time-dependent drop in the Photo-Luminescence (PL), which was attributed to the thermally induced ionization of the Eu2+ optically active centers. Several analytical techniques, including spatially and spectrally resolved PL, Electron Paramagnetic Resonance (EPR) and X-ray Photo-emission Spectroscopy (XPS) were used to support this hypothesis and to gain insight on the degradation process. By means of further tests, evidence of this degradation process was also found on samples stressed under a relatively low power density of 3 W/mm2 at 405 nm. This indicated that the optically (and thermally) induced ionization of the optically active species is the most critical degradation process for this family of phosphorescent material. The operating limits of a second-generation Eu-doped halophosphate phosphor were also investigated by means of short-term stress under optical excitation. The experimental data showed that a threshold excitation intensity for continuous pumping exists. Above this threshold, decay of the steady-state PL performance and non-recoverable degradation of the material were found to take place. This behavior is a consequence of the extremely harsh excitation regime, mainly due to the thermal management capabilities of the substrate material employed for our experimental purposes rather than from intrinsic properties of the phosphors.

Recycling of rare earths from lamp phosphor waste: Enhanced dissolution of LaPO4:Ce3+,Tb3+ by mechanical activation

With the promoted use of compact fluorescent lamps and the increasing amount of stockpiled compact fluorescent lamp waste, lamp phosphors are becoming an interesting secondary source for critical metals (yttrium, europium and terbium). This paper explores on the mechanism of a new potential hydrometallurgical route to improve the recovery efficiency of rare-earth elements from the green phosphor LaPO4:Ce3+,Tb3+ using mechanical activation as a pretreatment step prior to leaching. By applying an intense frictional action, the leaching yields of rare-earth elements were enhanced from 0.9% to 81% at room temperature, as a consequence of the change in activation energy. The shrinking core model was employed for modelling the leaching kinetics of the rare-earth elements and to calculate the decreasing apparent activation energy of the unmilled and milled samples (from 68 kJ mol−1 to 1.4 kJ mol−1). This difference can be explained by the physicochemical changes, including structural decomposition, specific surface area increase and particle size reduction, which were related to the corresponding leaching pattern. The optimized mechanical activation procedure was successfully applied to lamp phosphor waste, containing a mix of different phosphors. After sequential removal of the halophosphate phosphor and the red YOX phosphor, 99.0%, 87.3% and 86.3% of La, Ce and Tb present in the LaPO4:Ce3+,Tb3+ phosphor could be dissolved. These observations provide more insight in the mechanical activation process and may contribute to a more sustainable alternative route to the rare-earth element recycling industry.

Orange-red luminescence in KAl1−xPO4F:Eux3+ (0.1 ≤ x ≤ 1.0) halophosphate phosphor by a novel facile combustion method

Red-emitting phosphor KAl1-xPO4F:Eux3+ (0.1≤x≤1.0) were fabricated by combustion process at temperature 750°C. The XRD patterns did not indicate presence of the starting constituents and other likely phases which are an indirect evidence for the formation of the desired compound. The photoluminescence study shows that the intensity of electric dipole transition (5D0→7F2) at 613nm dominates over that of magnetic dipole transition (5D0→7F1) at 595nm. The FTIR also shows peaks appearing at 585.41–827.92cm−1 and 912.99–1074.12cm−1 correspond to the bending vibrations (v4 region) and stretching vibrations (v3 region) of PO43− group, respectively. The chromaticity coordinate of KAlPO4F:Eu3+ phosphor (x=0.674, y=0.325) is much closer to National Television Standard Committee (NTSC) standard value for red phosphor (x=0.670, y=0.330). All the spectrum features indicate that KAlPO4F:Eu3+ might be a promising phosphor for lighting or w-LEDs.

Analysis of electron-vibrational interaction in interconfigurational 5d➔4f transition of Eu2+ ions in Na5 Ca4 (PO4 )4 F.

In this paper, the photoluminescence properties of Eu2+ -activated greenish-blue-emitting halophosphate phosphor Na5 Ca4 (PO4 )4 F were studied to estimate electron-vibrational interaction (EVI) parameters such as the Huang-Rhys factor, effective phonon energy, Stokes shift and zero phonon line (ZPL) position for various concentrations of dopant. The validity of the results was established by modeling the emission spectra, which was found to be in good agreement with the experimental photoluminescence spectra. Copyright © 2016 John Wiley & Sons, Ltd.

Effective red-orange emitting CaMgPO4Cl:Sm3+ halophosphate phosphor

Red-orange Sm3+ doped in CaMgPO4Cl halophosphate phosphor excited at 405nm was prepared by combustion synthesis. The structure and properties were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence (PL) technique. The photoluminescence properties were studied by taking excitation and emission spectra and gives red-orange which corresponds 4G5/2→6H7/2 transition of Sm3+. CaMgPO4Cl:Sm3+ halophosphate phosphor may be good candidate for white LED lighting application.

Blue-Emitting Eu-Doped (Sr, Mg)5(PO4)3Cl Phosphor Particles Prepared by Spray Pyrolysis from the Spray Solution Containing Ammonium Chloride

Blue-emitting strontium magnesium halophosphate phosphor particles were prepared by spray pyrolysis from the spray solutions with ammonium chloride. The ammonium chloride was used as the source of chlorine and the flux material. The prepared (Sr, Mg)5(PO4)3Cl : Eu2+ phosphor particles had regular morphologies and fine sizes. The mean sizes of the (Sr, Mg)5(PO4)3Cl : Eu2+ phosphor particles were each 1.2 and 1.9 μm when the ratios of strontium to chlorine components were 1 : 0.5 and 1 : 1. The ratios of strontium to chlorine components in the as-prepared and post-treated particles were each 1 : 0.26 and 1 : 0.21. The (Sr, Mg)5(PO4)3Cl : Eu2+ phosphor particles that were prepared from the spray solution with the ratio of strontium to chlorine components of 1 : 1.5 had the maximum photoluminescence intensity, which was 176% of that of the commercial BaMgAl10O17 : Eu2+ phosphor particles under excitation wavelength of 400 nm.

Feasibility of an efficient recovery of rare earth-activated phosphors from waste fluorescent lamps through dense-medium centrifugation

Experiments were carried out with waste phosphors collected during the recycling of end-of-life fluorescent lamps to obtain a highly enriched phosphors product as starting material for the better extraction of rare earth elements. The aim of this work was therefore to separate low-density calcium halo-phosphate phosphors from high-density rare earth-activated phosphors through dense-medium centrifugation (with di-iodomethane as organic dense-medium). The feasibility of the process and the conditions for a good separation (higher Newton's efficiency) appear to be a function of the rotation speed of the centrifugal separator, the pulp concentration and the adsorption of a surfactant (sodium oleate, NaOl) during the pre-treatment stage. The effect of the centrifugation time was less pronounced. Through this study, a sink product assaying 48.61% of rare earth-activated phosphors could be recovered from waste phosphor materials pre-treated with 5 × 10 −5 mol/dm 3 of sodium oleate (NaOl) surfactant. The Newton's efficiency and recovery of the separation were 0.84 and 97.34%, respectively. The process feasibility was reinforced by the possibility to recover, through laboratory batch tests, more than 99.8% of the di-iodomethane (CH 2I 2).

Characteristics of Halophosphate Phosphor for Long-wavelength UV Prepared by Spray Pyrolysis

Blue-emitting <TEX>$Sr_{10}$</TEX>(<TEX>$PO$</TEX>)<TEX>$_{6}$</TEX> <TEX>$Cl_2$</TEX>:<TEX>$Eu^{2+}$</TEX> and <TEX>$_{(Sr,Mg) }$</TEX> 10/(<TEX>$PO_4$</TEX>)<TEX>$_{6}$</TEX> <TEX>$Cl_2$</TEX>:<TEX>$Eu^{2+}$</TEX> phosphor particles for application of long-wavelength UV LED were prepared by ultrasonic spray pyrolysis. The luminescence characteristics under long- wave-length ultraviolet of the <TEX>$Sr_{10}$</TEX> (<TEX>$PO_4$</TEX>)<TEX>$_{6}$</TEX> <TEX>$Cl_2$</TEX>:<TEX>$Eu^{2+}$</TEX> and (Sr,Mg)<TEX>$_{10}$</TEX> (<TEX>$PO_4$</TEX>)<TEX>$_{6}$</TEX> <TEX>$Cl_2$</TEX>:<TEX>$^Eu{2+}$</TEX> phosphor particles prepared by the spray pyrolysis were compared with that of the commercial product. The PL intensity of the <TEX>$Sr_{10}$</TEX> (<TEX>$PO_4$</TEX>)<TEX>$_{6}$</TEX> <TEX>$Cl_2$</TEX>:<TEX>$Eu^{2+}$</TEX> particles prepared by the spray pyrolysis was lower than that of the commercial <TEX>$Sr_{10}$</TEX> (<TEX>$PO_4$</TEX>)<TEX>$_{6}$</TEX> <TEX>$Cl_2$</TEX>:<TEX>$Eu^{2+}$</TEX> particles because prepared <TEX>$Sr_{10}$</TEX> (<TEX>$PO_4$</TEX>)<TEX>$_{6}$</TEX> <TEX>$Cl_2$</TEX>:<TEX>$Eu^{2+}$</TEX> phosphor particles had porous structure and hollow morphology. However, the PL intensity of the (Sr,Mg)<TEX>$_{10}$</TEX>(<TEX>$PO_4$</TEX>)<TEX>$_{6}$</TEX> <TEX>$Cl_2$</TEX>:<TEX>$Eu^{2+}$</TEX> phosphor particles prepared by the spray pyrolysis was 8% higher than that of the commercial one. The high brightness of <TEX>$(Sr,Mg)_{10}$</TEX> (<TEX>$PO_4$</TEX>)<TEX>$_{6}$</TEX> <TEX>$Cl_2$</TEX>:Eu<TEX>$^{2+}$</TEX> phosphor particles prepared by spray pyrolysis is due to the dense structure and high crystallinity of particles. The TEX>$(Sr,Mg)<_{10}$</TEX> (<TEX>$PO_4$</TEX>)<TEX>$_{6}$</TEX> /<TEX>$Cl_2$</TEX>:<TEX>$Eu^{ 2+}$</TEX> phosphor particles had main emission peak t 448 nm under long- wavelength ultraviolet.

Luminescence Characteristics of Eu-doped Strontium Halophosphate Phosphor Particles Prepared by Spray Pyrolysis

Eu-doped strontium halophosphate phosphor particles were first prepared by spray pyrolysis from various types of precursor sources and their luminescence characteristics were investigated. Phase-pure halophosphate particles were obtained when ammonium phosphate and ammonium dihydrogen phosphate were used as phosphorous source, while halophosphate particles were not obtained using phosphoric acid. Spherical and nonaggregated particles were obtained when ammonium phosphate and ammonium dihydrogen phosphate were used. However, the particles prepared from phosphoric acid were strongly aggregated. The particles prepared from the mixture of strontium nitrate and strontium chloride as strontium and chlorine sources, had a spherical shape and are nonaggregated. The particles prepared from strontium nitrate, strontium chloride and ammonium dihydrogen phosphate had the highest PL intensity among halophosphates due to their phase purity and spherical morphology.

Measurement of Mercury Bound in the Glass Envelope during Operation of Fluorescent Lamps

Mercury vapor is essential to the high efficiency conversion of electrical power to light in fluorescent lamps. However, the amount of mercury that must be added to the lamp to achieve a 20,000 h operating life is much larger than the amount of vapor needed for the discharge. This is a result of processes that bind the mercury during lamp operation and make it unavailable as mercury vapor. As part of an effort to determine the amount of mercury that must be added to standard GE F40T12 lamps with halophosphate phosphors we have measured the mercury bound in the soda‐lime glass under the phosphor in the positive column in a series of these lamps. From these measurements we have developed an empirical model which describes the amount of mercury per unit area that is bound in the glass as a function of operating time and the weight of phosphor over the glass.

Investigation of activator (Mn, Sb) speciation in phosphors for fluorescent lamps

The speciation of antimony and manganese (activators for fluorescent lamp phosphors) in samples of commercial calcium halophosphate phosphors for fluorescent lamps was investigated. The total antimony content was determined by flame atomic absorption spectrometry (FAAS), and the antimony(III) content by controlled-current coulometric titration. A method for examination of manganese speciation was proposed. Manganese forms were investigated by the partial dissolution technique using various agents and by FAAS analysis. The proposed methods can successfully be applied for control of phosphor properties and manufacturing processes.

Determination of the antimony substitution site in calcium fluorapatite from powder X-ray diffraction data

Comparison of powder X-ray diffraction data from a 2-2 wt% antimony-substituted calcium fluorapatite [0.185 Sb atoms per unit cell containing CaloF2(PO4)6] with data from an undoped sample shows electron density changes corresponding to antimony substitution at the Ca(2) (mirror) site. Many properties of this 2.2 wt% Sb sample indicate that it corresponds to commercial halophosphate phosphors of lower Sb concentration. Differing properties are shown by a 3.1 wt% Sb sample for which no diffraction evidence is found for substitution at the Ca(2) site, but for which electron density difference maps do suggest substitution at the Wyckoff 2(c) and 2(d) sites of P63/m, between Ca(l) (threefold) positions. Both Rietveld refinements and Fourier inversion of the differences between observed intensities were used to reach these conclusions.

DTA investigations on the synthesis of halophosphate-type phosphors

The effects of temperature, heating rate and the protective atmosphere used during synthesis on the luminous properties of the Polish halophosphate phosphor H 11 were studied. From the results, optimum synthetic conditions are suggested.

Location of antimony in a halophosphate phosphor.

The location of antimony in halophosphate phosphors has been probed by use of $^{121}\mathrm{Sb}$ M\"ossbauer spectroscopy. It has been shown that the observed M\"ossbauer parameters can be understood if the antimony is at the phosphorous site, its ligands being three of the oxygen atoms of the phosphate group and a fluorine ion. The problem of maintenance of the halophosphate phosphors in relation to loss of the fluorine ions and to the ${\mathrm{Sb}}^{5+}$ concentration associated with an impurity phase has also been studied.

Eu&lt;SUP&gt;2+&lt;/SUP&gt;付活ハロりん酸塩蛍光体とその3波長形蛍光ランプへの応用

Eu&lt;SUP&gt;2+&lt;/SUP&gt;付活ハロりん酸塩蛍光体とその3波長形蛍光ランプへの応用

3波長帯形けい光ランプの照明効果

The three-band-type fluorescent lamp (3-Band) has a unique spectral power distribution which has been optimized to increase both the general color rendering index (CRI) and the lamp efficacy and it is sometimes said that the lamp has some particular effects more than estimated from the CRI and the efficacy. These effects of the lamp has been examined from various view points in compariosn with other commercial lamps.Colorimetric calculations show that the 3-Band illumination is not suitable for color discrimination problem though it has practicall no problem, in the color perception of surface colors in the usual environment. The 3-Band has good performance in the color rendition for human complexion, and it becomes more preferred in some aspects under the 3-Band added with the halophosphate phosphor than that of the pure type. The 3-Band has unique effects on the brightness and the visual clarity of illumination compared with the other lamps of not only standard types of cool white and daylight color lamps but also de-luxe lamps which have a higher CRI with the broad band continuous spectral distribution.The authors propose a new numerical expression to distinguish the 3-Band from the other types of lamp. That is the ratio of the power in the three spectral regions (445-475, 525-555, 595-625 nm) to the total power (400-700 nm).

Thermoluminescence and thermoluminescence spectra of synthetic fluorapatite

On account of their fairly long life, alkaline earth halophosphate phosphors are still the mainstay of the fluorescent lamp industry. For higher efficiency and an increased selection of spectral distribution, with minor variation in composition and dopants, halophosphates are synthesised nowadays. It is not surprising, therefore, that these synthesised apatite phosphors are still attracting the attention of the research workers too. In this paper the results of TL and TL spectra of X-irradiated synthetic fluorapatite are reported with a view to understand the nature of the recombination processes in the system, vis-à-vis the defects created by irradiation. Such studies are ultimately aimed at unravelling the causes for the fatigue and quantum efficiency changes that are occuring at present in such phosphors.

A new deluxe fluorescent lamp with a color rendering index of 99

Fluorescent lamps were studied to improve color rendering property without the use of filter to absorb blue-violet radiations. The general color rendering index (Ra) is possible to be raised effectively, when are controlled both blue-violet mercury lines and continuous radiations emitted from phosphors. A new strontium-borophosphate phosphor, with a chemical formula of [2 (Sr, Eu) O·0.84P2O5·0.16B2O3], was developed and its application in fluorescent lamp of accurate color rendition was examined. This phosphor absorbs not only ultra-violet radiation but also the visible blue radiation and emits bluish green light, having lower radiant power in blue-violet spectral region than usual antimony activated calcium halophosphate phosphor. The use of this phosphor is very effective to control the radiant power in blue-violet spectral region, and makes it possible to produce fluorescent lamps having Ra value of 99 and luminous efficacy of 60 lm/w, without the use of the filter for absorbing blue-violet radiations.

Fluorescent lamps with very high luminous efficiency

Some years ago a new generation of fluorescent lamps with 80 Im/W and a colour rendering index of 85 was developed, which used newly developed phosphors with narrow emission bands. Recent improvements in these phosphors have opened up new possibilities as far as lamp geometries are concerned. For example, 1200 mm 40 W lamps in 25 mm diameter with about 95 Im/W, a colour rendering index of 85 and a lumen maintenance which is better than that of 37 mm diameter 40 W lamps with halophosphate phosphors, can now be realized. The newly developed lamps therefore have 15 to 20% higher efficacies than existing standard lamps, and provide an answer to the increasing demand for energy conservation.