Crystal Phosphors Research Articles

Characteristics of long afterglow phosphorescent calcium aluminate crystals for fluorescence thermometer application

Temperature dependence of photoluminescence (PL) peaking at wavelength of λ = 440 nm from FZ grown CaAl 2 O 4 ; Eu, Dy phosphor crystal is evaluated for a fiber-optic thermometer application. The PL lifetime from the specimens decreases greatly from 11.24 to 1.17 ms as the temperature increases from 305 to 458 K. The temperature coefficient of PL lifetime, - 0.17 ms / K , in the narrow temperature range from 305 to 345 K is larger than that of ruby (Cr doped Al 2 O 3 ) whose PL lifetime is 4 ms and temperature coefficient is - 0.169 ms / K . The large temperature coefficient of PL lifetime of CaAl 2 O 4 : Eu, Dy phosphor crystal is due to the trap levels generated by Dy doping.

Kinetics of Relaxation of Stored Light Sums in Silver Chloride

Experimental investigation of the time and temperature dependences of the process of relaxation of excited silver chloride has been carried out by the method of a photostimulated burst of luminescence. It is found that the relaxation process can be divided into two components, the rates of which differ by an order of magnitude. The activation energies of these processes of 0.03 and 0.06 eV correspond to the thermal ionization energies of electrons from shallow traps. Thermally activated relocalization of charges from shallow to deep traps in the process of relaxation has been revealed. The depth of a corresponding trap appeared equal to 0.17 eV. A model of a crystal phosphor has been suggested that contains five levels in the forbidden band: a hole center of recombination (luminescence), a deep electron trap, two shallow electron traps located at a depth of 0.03 and 0.06 eV from the bottom of the conductivity band, and a hole trap located at a height of 0.17 eV from the valence band top. Within the framework of this model, we can qualitatively explain the time and temperature dependences of stored light sums. We have shown the possibility of applying the method of a photostimulated burst of luminescence to investigation of the processes of relaxation of electron excitations in crystals to establish the relaxation mechanisms.

Fibre-optic thermometer using sensor materials with long fluorescence lifetime

A fibre-optic thermometer using newly developed phosphor sensor materials is described. A highly sensitive fibre-optic fluorescence thermometer is developed using chromium ion (Cr3+) doped phosphor crystals with a longer lifetime than that of conventional ruby sensors. Long fluorescent europium doped strontium aluminate phosphors co-doped with various auxiliary activators (SrAl2O4:Eu2+, Ln3+, Ln = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), were also grown and evaluated. In the fibre-optic thermometer using Cr3+ doped phosphor, PL lifetime decreased at temperatures ranging from 270 K to 750 K. The sensitivity of the fibre-optic thermometer varies with the host materials of Cr3+ ions. In the fibre-optic thermometer using SrAl2O4:Eu2+, Ln3+ doped phosphor, the value and lifetime of afterglow phosphorescence from the SrAl2O4:Eu2+, Ln3+ phosphors varied greatly in the narrow temperature region because the afterglow phosphorescence was dominated by thermal excitation of trapped carriers. Since the trap depth and the trap density depend on auxiliary activator elements, the sensitivity and temperature range of the fibre-optic thermometer using SrAl2O4:Eu2+, Ln3+ phosphors varied with auxiliary activator elements of SrAl2O4:Eu2+, Ln3+ phosphors.

Facile method of infilling photonic silica templates with rare earth element oxide phosphor precursors

A method for preparing rare-earth element-doped yttrium oxide phosphor photonic band gap crystals (PBG) is described, which obviates the necessity for multiple infilling of the opal-like template. The method utilizes (i) the re-dissolving and the concentration of previously precipitated spherical phosphor particles made by homogeneous precipitation methods into a viscous precursor phosphor solution, and (ii) formation of an opal-like template of polystyrene or silica spheres. A procedure is outlined that permits the precursor solution to be drawn into the template in a controlled manner that can be easily monitored using an optical microscope. Attenuation of the strong, red cathodoluminescent emission is observed in Y2O3:Eu3+ phosphor PBG crystals that are engineered to have a stopband overlapping the emission bands in the red region. This attenuation results from Bragg diffraction of the light emitted within the PBG phosphor crystals.

ZnS‐based photonic crystal phosphors fabricated using atomic layer deposition

AbstractThe infiltration by atomic layer deposition of three‐dimensional opal structures has been investigated as a means of fabricating photonic crystal phosphors. ZnS:Mn infiltrated and inverse opals have been demonstrated with filling fractions >95%. Characterization of these structures by scanning electron microscopy, specular reflectance, and photoluminescence is reported. Specular reflectance measurements confirm successful infiltration, and demonstrate modification of the electromagnetic density of states consistent with calculated photonic (111) pseudo band gaps. Photoluminescence measurements reveal modification of emission by the photonic crystal consistent with angular dependent specular reflectance measurements. These results reveal a flexible and convenient route for fabricating high performance photonic crystal structures and optical microcavities. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fiber-optic thermometer using Cr-doped YAlO3 sensor head

Cr-doped YAlO3 phosphor crystals have been grown and characterized for applications in fiber-optic thermometers based on the temperature dependence of the photoluminescence (PL) lifetime. PL peaking at λ=735 nm is observed from the crystals following an excitation by a light-emitting diode at λ=520 nm. Long PL lifetime (τ=43.14 ms) is observed from Cr-doped YAlO3 at room temperature as compared with those of ruby (τ=4.2 ms) and spinel (τ=8.0 ms). The temperature coefficient (−0.075 ms/K) of Cr-doped YAlO3 is also larger than those of ruby (−0.010 ms/K) or spinel (−0.037 ms/K). YAlO3 is considered to be a sensitive sensor head material for fiber-optics thermometers.

長残光蛍光体の発光寿命・残光強度の温度依存性評価(機能性結晶III)

長残光蛍光体の発光寿命・残光強度の温度依存性評価(機能性結晶III)

LP‐4: Late‐News Poster: The First Cathodoluminescence Spectra from Photonic Band Gap Phosphors for Low Voltage Applications

AbstractIt is demonstrated under e‐beam excitation at low voltages that, using cubic Y2O3: Eu as an example, photonic phosphor crystals offer the opportunity of altering the emission band signature of the phosphor. The conclusion is that nano‐structured phosphor lattices can now be designed and tailored for low voltage applications.

On the improvement of detection characteristics of trans-stilbene crystals by improving crystal perfection

Organic molecular scintillating crystals are noted for their good timing and particle discrimination process. Trans-stilbene is one such candidate noted for its good particle detection characteristics for the past five decades. Progressive strengthening of detection characteristics of trans-stilbene has been attempted by improving crystal perfection. A series of timing resolution studies have been carried out for the Bridgman grown trans-stilbene crystals under different experimental conditions. The results were compared with the previously reported values. Pulse shape discrimination process has been carried out for 241Am and 252Cf sources and good discrimination has been obtained for gamma-alpha and gamma- neutron sources from the grown organic phosphor crystal.

4.4: Photonic Phosphor Crystals for Display Applications

AbstractIt is shown that photonic phosphor crystals potentially offer a number of opportunities for improving photoluminescent, electroluminescent and cathodoluminescent devices. The synthesis of 3‐dimensional photonic phosphor crystals is discussed and examples of T.E.M. micrographs and optical diffraction patterns are presented. The modification of the emission properties of these crystals due to their microstructure is discussed.

Cathodoluminescence of blue ZnGa2O4 with In2O3-mixed phosphor

In this work, the cathodoluminescence (CL) of the ZnGa2O4 phosphor for different composition ratios of ZnO/Ga2O3 is examined, and its emission behavior is compared with that of ZnGa2O4 with In2O3-mixed phosphor. The wavelength and intensity of CL vary with the crystallization of phosphor; as a consequence, the optimal crystallization and luminescence are obtained when the molar ratio of ZnO/Ga2O3 is 1. The luminance intensity is 4.2 times enhanced when phosphor is mixed with 12 wt.% of In2O3. A maximum luminance of 503 cd/m2 and a optimal conductivity of 0.69 (MΩ m)−1 of phosphor are obtained. The CL of blue ZnGa2O4 phosphor will be enhanced by In2O3 mixed.

Synthesis and luminescent properties of Mn2+-doped zinc silicate phosphors by sol–gel methods

Abstract Green light emitting Mn2+-doped Zn2SiO4 phosphor nano-particles were synthesized by a sol–gel method combined with a furnace firing. All samples were prepared at various temperatures and times both with and without a polymeric surfactant to determine if the particle size can be tailor-made over a significant range. The particle size of all the powder samples was measured through dynamic light scattering, which showed a mean particle diameter between 30 nm and 1 μm depending on the conditions. Final manganese amounts were determined by inductively coupled plasma spectroscopy. The microstructure of phosphor crystals was characterized by X-ray diffractometry (XRD) and scanning electron microscopy. XRD results indicate that seeds play an important role in enhancing the nucleation and crystallization of Zn2SiO4:Mn2+. Green photoluminescence (PL) and cathodoluminescence (CL), whose emission peak is located at 522 nm, were observed from the synthesized phosphor particles under UV excitation and electron bombardment. Results show that the non-seeded samples with a mean diameter of 30 nm displayed a significant increase in PL brightness over the seeded samples whose mean diameter was 215 nm. In contrast, XRD results show that the seeded samples were more crystalline than the non-seeded samples. PL and CL intensity lagged behind the bulk reference sample due to a high manganese loss in processing.

Growth and characteristics of calcium aluminate phosphor crystals

Growth and characteristics of calcium aluminate phosphor crystals

Characterization of trap levels in long-duration phosphor crystals

A mechanism for the long-duration phosphorescence from Eu 2+ ions in SrAl 2O 4 crystals has been studied by evaluating the energy level and the density of the traps generated by the auxiliary activators. SrAl 2O 4:Eu 2+ crystals doped with Nd, Sm, Gd, Dy and Y have been grown by the floating zone technique. Trap depth and trap density are evaluated by the thermally stimulated luminescence technique. A tentative energy diagram for the traps in the crystals has been drawn based on the hole-trap model. The trap levels vary from 0.0024 to 0.78 eV with the added elements. The long-duration phosphorescence is influenced strongly by the depth and the density of the traps. The traps at around Et=0.5 eV, which are seen in Dy- and Nd-doped specimens, are responsible for the long-duration phosphorescence.

Development of high spatial resolution X-ray CT system at BL47XU in SPring-8

High spatial resolution, micrometer range, X-ray CT system has been developed at SPring-8. The experiments were performed at the undulator beam line BL47XU. An “in-vacuum type” undulator is employed as an X-ray source, and the X-rays are monochromatized with a liquid nitrogen cooled Si(1 1 1) double crystal monochromator. High precision rotation stage with air bearing was used for sample rotation. The transmitted images were obtained with a two-dimensional image detector, which consists of a single crystal phosphor screen (Lu 2SiO 5 : Ce), an objective lens and a cooled CCD camera. In this system the smallest effective pixel size was set to 0.5 μm×0.5 μm. As a result of the experiments, three-dimensional images of a few micrometer-order texture has been successfully obtained with the developed CT system.

Synthesis and luminescent properties of Mn 2+ doped Zn 2SiO 4 phosphors by a hydrothermal method

Green light emitting Mn 2+ doped Zn 2SiO 4 phosphor particles were synthesized by a seeded hydrothermal method at 230°C for 2 h. The microstructure of phosphor crystals was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). XRD results indicate that seeds play an important role in enhancing the nucleation and crystallization of Zn 2SiO 4 crystals. Green photoluminescence, whose peak is located at 522 nm, was observed from the hydrothermally synthesized phosphor particles under UV excitation. Cathodoluminescence (CL) efficiency was weak and increased with increasing applied voltage up to 0.30 lm W −1 at 10 kV. The weak CL efficiency is believed to be caused by the polymer adsorbate, used to control the particle size, on the Zn 2SiO 4 particle surface.

High luminance YAG single crystal phosphor screen

Epitaxial phosphors of Ce,Tb:YAG containing Lu 3+ and Ga 3+ on YAG (yttrium aluminum garnet) single crystal faceplates have properties which are suitable for projection CRTs. The external efficiency of the single-crystal YAG screen is relatively low. Truncated cone geometry can increase the external efficiency by a factor of 5.2, if such a shape can be formed in the phosphor layer. An anisotropy etching process of YAG has been developed for the fabrication of a YAG luminescent screen with truncated square mesas. A large fraction of the cathodoluminescent can be directed through the untextured front surface of the crystal. An improvement in phosphor efficiency by a factor of 2.3 has been achieved.

Mechanism of dissipation of the excitation energy in garnet oxides doped with rare-earth ions with 4f-5d transitions

Mechanisms of dissipation of the excitation energy in garnet crystal phosphors Y3Al5O12 and Y3Ga5O12 doped with rare-earth ions with interconfiguration transitions are studied depending on the Ga concentration.

Sol-Gel Luminophors Based on Diopside

A relationship is established between the conditions of sol-gel synthesis of powders, their crystallization capacity, and the luminescence properties of crystal phosphors of the composition CaMgSi2O6 : Ti4+. The properties of materials produced using one-stage and two-stage procedures for heat treatment of the gels are compared. It is shown that the calcination stage has a positive effect on the crystallization process and on the luminescence properties of the articles, and the calcination-stage temperature is a deciding factor in optimization of the heat-treatment procedure.

Electronic states on the surface of zinc sulfide crystal phosphors

An optical method of heterogeneous spectroscopy of the surface has been developed, which makes it possible to determine the energy position of electronic states on the surface itself of wideband solid bodies. The method is based on a new phenomenon discovered by us which is a highly efficient heterogeneous electronic accommodation of the energy of heterogeneous chemical reactions; it consists specifically in an increase, by 3–5 orders of magnitude, in the rate of generation of electrons by reaction energy to the C-zone of a crystal existing in the metastable state as compared with an unexcited specimen. We have determined the energy denths of electronic states that participate in accommodation of the reaction energy of heterogeneous recombination of atoms for a large number of zinc sulfide crystal phosphors.