Polycrystalline Phosphors Research Articles

Controllable white light emission from Dy3+–Eu3+ co-doped KCaBO3 phosphor

Potassium calcium borate, KCaBO3:Eu3+ phosphors with various Dy3+ concentrations (0–3 wt%) were synthesized by solid state reaction and studied for the first time. Under various UV–violet excitations, the obtained single monoclinic phased Dy3+–Eu3+ co-doped KCaBO3 polycrystalline phosphors emit a combination of yellow–blue and red–orange wavelength giving intense white light, which can easily be controlled by varying the concentration of Dy3+. The increase in white light emission with the increase of Dy3+ concentration indicates the efficient energy inter-ion transfer from Dy3+ to Eu3+ ions. Furthermore, the observed emission lifetimes and the intense white light emission are suggestive exploration for the present phosphor for potential optoelectronic applications such as white light-emitting phosphor for blue LEDs chips.

Thermoluminescence properties of rare earth doped lithium magnesium borate phosphors

This paper reports the thermoluminescence (TL) properties of rare earth doped lithium magnesium borate (LMB) polycrystalline phosphor. LMB phosphor has been prepared by high temperature solid state diffusion method. Among all the rare earth doped LMB phosphors, terbium doped material has shown maximum TL sensitivity with a broad dosimetric glow peak at 240 °C. near the tissue equivalent TL phosphor with terbium dopant has about four times the TL sensitivity of TLD-100. The main dosimetric properties such as glow curve stability, TL response versus absorbed dose, post-irradiation storage stability, and reusability are investigated. This TL material has a linear dose response up to 10 3 Gy, negligible storage fading and a simple annealing procedure for reuse. The TL emission spectra of LMB:Tb 3+ showed broad green emission at 544 nm, which merged with host emission. The characteristic Tb 3+ emissions are seen in the photoluminescence (PL) spectra.

Strong green upconversion emission from Er 3+–Yb 3+ co-doped KCaBO 3 phosphor

Potassium calcium mixed borate, KCaBO 3:Er 3+, phosphors with varied Yb 3+ concentrations were synthesized by solid-state reaction and studied for the first time. The obtained single monoclinic phased polycrystalline phosphor has the capability of accepting the Yb 3+ sensitizer up to 16 wt.%. Monotonically increasing green upconversion emission ( 2H 11/2, 4S 3/2 → 4I 15/2) of Er 3+ with the increase of Yb 3+ concentration is observed under 980 nm laser excitation. Upconversion mechanism is investigated in detail and attributed to the efficient resonant energy transfer from Yb 3+ to Er 3+ ions in such system. Our results suggest a potential material for green upconversion phosphor.

Sol–gel preparation and luminescence of RE3BO6: Dy3+ (RE = La, Y, Gd) microparticles with hybrid precursors

Dysprosium ion activated RE3BO6 (RE = La, Y, Gd) polycrystalline phosphors have been prepared via a modified sol–gel process with urea as fuel and rare earth nitrates as precursors. The crystal phase and the morphology of the phosphors are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average particle size after heat treatment at 1,000 °C is around 5 μm by particle size determination technique. The characteristic transitions of Dy3+ due to 4F9/2 → 6H15/2 (blue) and 4F9/2. → 6H13/2 (yellow) can be observed in the emission spectra and the yellow-to-blue intensity ratio (Y/B) can be changed with the variety of the doped concentration of Dy3+ ion. Zeta potential shows the relationship between the surface charges to the pH value in suspension.

Modified submicron luminescent materials based on the Y2O3:Eu and Y2O2S:Eu polycrystals for full-color video-imaging devices and light sources

Modifying the polycrystalline phosphors Y2O3:Eu and Y2O2S:Eu in order to allow their application as submicron composite materials for electrovacuum luminescent video-imaging devices and light sources is considered. The effect of synthesizing such materials through the use of H3BO3 on their crystal structure, spectral characteristics, and photo- and cathodoluminescence intensities is investigated.

Upconversion luminescence properties of Li+-doped ZnWO4:Yb,Er

Upconversion luminescence (UPL) characteristics and effects of Li+ion on the UPL of ZnWO4:Yb,Er polycrystalline phosphors were investigated. It was shown that introduction of Li+ions could reduce the calcination temperature by about 200 °C and increase the crystallinity of ZnWO4:Yb,Er by a liquid-phase sintering process via formation of Li2WO4and other intermediates. UPL efficiency is remarkably promoted by Li+ions. Moreover, the UPL spectrum of Li+-doped ZnWO4:Yb,Er presents a red shift, and the strongest peak position shifts from 553 to 559 nm. These can be attributed to a shift in the 4f level barycenter to lower energy, which results from lowering of the symmetry of the crystal field around Er3+.

Photoluminescent properties of Dy3+-activated REAl3(BO3)4 (RE=Y, La, Gd) polycrystalline phosphors from hybrid precursors

Abstract Dysprosium-activated REAl 3 (BO 3 ) 4 (RE = Y, La, Gd) polycrystalline phosphors were synthesized via in situ sol–gel process using urea as fuel and metal nitrates as precursors. The uniformity phase of the phosphors was checked by X-ray diffraction (XRD) technique. Scanning electron microscopy (SEM) investigations were carried out to study the surface morphological features and the particle size of the phosphor after heat treatment at 1000 °C. The excitation spectra show strong spectral bands in region of 220–450 nm. The characteristic transitions of Dy 3+ due to 4 F 9/2 → 6 H 15/2 (blue) and 4 F 9/2 → 6 H 13/2 (yellow) were observed in the emission spectra and the yellow-to-blue intensity ratio changed with the variety of the doped concentration of Dy 3+ . The results can be benefit for the white-color luminescent materials.

Luminescence study in Eu-doped aluminum oxide phosphors

α- and γ-(Al1−xEux)2O3 polycrystalline phosphor powders have been prepared via pressure assisted combustion synthesis at ∼280 °C. The particle size could be controlled (nanoparticles/microparticles) by adjusting the initial pressure in the combustion reactor. Upon excitation at 394 nm, the Eu-doped alumina nanoparticles exhibited a strong photoluminescence due to a parity forbidden f–f intraconfigurational transition upon excitation at λ = 395 nm. By analyzing the emission lines in the cathodoluminescence spectrum of the europium doped α-Al2O3 sample it was inferred that the dopant ions occupy low symmetry sites in the host lattice. These powders are potentially good candidates for photonics applications.

Determination of recombination parameters of phosphors from cathodoluminescent characteristics

A simple method to determine recombination parameters of polycrystalline phosphor materials is proposed based on a comparison of a theoretical prediction of cathodoluminescent intensity with experimental characteristics. The obtained parameters are very sensitive to additional treatments of phosphor surface, especially to chemical modification by even small amounts of inorganic oxides. The proposed method offers a simple and rapid way of controlling recombination parameters of luminescent materials.

Cooled CCD camera with tapered fibre optics for electron microscopy

A CCD camera for use in electron microscopy, with 1286 × 1152, 37 μm pixels and an input aperture of 60 mm diameter, is described in this paper. An attempt is made to optimise the phosphor resolution for 120 keV electrons using Monte-Carlo simulation methods. Incident electrons are converted to visible light in a polycrystalline phosphor (P43) deposited on tapered fibre optics and imaged on to a cooled slow-scan CCD which is controlled from a Sun sparc-station, running under a Unix platform, through a VME-based drive and read-out electronics system. The camera is attached to a Philips CM12 microscope and is used mainly for recording electron-diffraction patterns from two-dimensiónally ordered protein arrays. Data can be displayed rapidly on the Sun monitor and can also be transferred for further analysis to a Dec Alpha computer via Ethernet for application of various image-processing programs.

CCD-based high resolution digital radiography system for non destructive evaluation

Film radiography has long served the aerospace industry as a principal method for hardware flaw detection. Although excellent in performance, this method is extremely time consuming, labor intensive, costly, and is unsuitable for real time inspections. Modern digital radiographic systems overcome some of these difficulties but are also limited in terms of speed of operation due to persistence of the sensor and a problematic tradeoff between the X-ray detection efficiency and spatial resolution. We are developing an innovative X-ray imaging detector consisting of a novel microstructured CsI scintillator coupled to a fiberoptic taper-based CCD. Thin-film deposition techniques, previously developed to produce thin, structured CsI screens have been extended to fabricate CsI screens, up to 450 mg/cm/sup 2/ (1,000 /spl mu/m) in thickness. These sensors are suitable to provide high detection efficiency with high image quality for NDE applications. A prototype high energy imaging system was constructed by integrating these screens into a fiber-optic-based CCD camera. The performance was compared to that of the same system using a standard polycrystalline phosphor for NDE imaging applications. The experimental evaluations were carried out at Scientific Measurement Systems, Inc., Austin, TX.

A high sensitivity imaging detector for electron microscopy

A camera for electron microscopy based on a low readout noise cooled-CCD is described in this paper. The primary purpose of this camera is to record electron diffraction from ordered arrays of proteins but also has potential applications in imaging, electron tomography and for the automatic alignment of the electron microscope. Electrons (energy ∼120 kV) which are scattered by the specimen to form the image, which is normally recorded on film, are converted to visible photons in a polycrystalline phosphor and the resulting image is stored on the CCD (EEV 05-20, 1152 by 814, 22.5 μm square pixels). The main advantages of using CCDs include a large dynamic range, very good linearity and the possibility of immediate access to the data which is in a digitised form capable of further processing on-line during the experiment. We have built specially designed CCD “drive” electronics in a VME crate, interfaced to a Sun Sparcstation, for controlling the CCD operations. Data reduction programs have been installed, previously used off-line, to speed up data processing, and provide analysed data within a few minutes after the exposure.

A Study of the Surface Texture of Polycrystalline Phosphor Films Using Atomic Force Microscopy

ABSTRACTStimulable phosphor thin films are being investigated for use as optical data storage media. We have successfully applied atomic force microscopy (AFM) to the measurement of the surface texture of these films. Determination of the surface texture of the films is important for evaluating the effect of surface quality on optical scatter. In other thin film material systems it has been found that the surface “bumps” revealed by AFM correspond to grains in the film. This is not the case for the stimulable phosphor films used in our study. We have determined the grain size of our phosphor films by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The grain size from TEM and XRD does not correlate with the size of the AFM surface “bumps.” For example, in two of the five films studied, the XRD derived grain size varies by a factor of two but the size of the surface “bumps” remains the same. We conclude that the texture of the film surface is not directly determined by the grain size of the phosphor material.

Luminescence des ions activateurs dans les matériaux inorganiques et applications

2014 We present the basic mechanisms of the absorption of the pumping radiation and the fluorescence emission of inorganic luminescent materials and we give the list of main compounds used by modern technology. Then, we show there were connections between polycrystalline phosphors and laser-material research. We insist on the present status and the future development of phosphors for fluorescent lighting, TV screens, X-ray intensifier screens and electroluminescent devices. Revue Phys. Appl. 21 (1986) 689-707 NOVEMBRE 1986, Classification Physics Abstracts 78.50 78.55

On the Physical Characteristics and Chemical Composition of Electroluminescent Phosphors

Through controlled removal of surface layers, it was found that surface chemical barriers are not responsible for electroluminescence in zinc sulflde phosphors. Polycrystalline phosphors are shown to be almost uniform with respect to chemical, physical, and electroluminescent properties as one passes from the surface into the crystallite bulk. Electron micrographs show the character of the particles as successive layers of phosphor surfaces are removed by acid etching. The experimental results at progressive stages of etching are interpreted in terms of an inefficient surface layer and of decreased particle size after etching. Regions capable of serving as the site of field intensification are held to exist throughout the volume of the particles.