Luminescence properties of CaS:Ce, Sm nanophosphors

CaS:Ce, Sm nanophosphors were synthesized via solid state diffusion method. X-Ray diffraction confirmed the cubic crystalline phase of CaS:Ce, Sm nanoparticles. The particle size calculated using Debye-Scherrer formula was found to be 52 nm. The morphological investigations of the nanoparticles were made using TEM and found to have nearly spherical morphology with diameter 45-50 nm, which is in close agreement with the XRD result. The PL emission characteristics of CaS:Ce, Sm as a function of cerium and samarium concentrations have been studied and CaS:Ce_0.6Sm_0.4 system has maximum emission intensity, hence it was opted for further studies. The CaS:Ce_0.6Sm_0.4 system showed independent emission of Sm and Ce when excited at 330 and 450 nm, respectively. To study the energy transfer between cerium and samarium, the CaS:Ce_0.6Sm_0.4 was excited at wavelengths other than the excitation wavelengths of Ce (450 nm) and Sm (330 nm). The existence of Ce emission (at an excitation of 390 nm) even in the absence of Ce excitation band and Sm emission at an excitation of 405 nm, which is the excitation band of Ce, indicates the energy transfer at these two wavelengths. Thermoluminescence characteristics of ⁶⁰Co irradiated CaS:Ce_0.6Sm_0.4 have been investigated for different doses of 0.14-125 Gy. All the glow curves show a single peak at 475 K. With increasing dose, the intensity of this peak increases and a shoulder is formed on the lower temperature side at 415 K at 21 Gy of exposure. CaS:Ce_0.6Sm_0.4 shows almost linear dose dependence up to 125 Gy.     

Enhanced luminescence and degradation of SiO2:Ce,Tb powder phosphors prepared by a sol-gel process

Enhanced green photoluminescence and cathodoluminescence (CL) from Tb³⁺ ions due to co-doping with Ce³⁺ ions were observed from SiO₂:Ce,Tb powder phosphors prepared by a sol-gel technique. Blue emission from the Ce³⁺ ions was completely suppressed by Tb co-doping, presumably due to energy transfer from Ce³⁺ to Tb³⁺. In addition, the green CL intensity from SiO₂:Ce,Tb degraded by ∼50% when the powders were irradiated for 10 h with a 2 keV, 54 mA/cm² beam of electrons in an ultra-high vacuum chamber containing either 1×10⁻⁸ or 1×10⁻⁷ Torr O₂. Desorption of oxygen from the surface was observed during the decrease of CL intensity. The mechanisms for energy transfer from Ce³⁺ ions to Tb³⁺ ions to enhance the green luminescence, and mechanisms for desorption of oxygen from the phosphor surface that would result in decreased CL intensity are discussed.     

Thermally stimulated luminescence and infrared studies of CaS : Bi,Tm phosphors

Calcium sulphide phosphors doped with bismuth and thulium are prepared from Indian minerals. The glow curves are recorded in the temperature range of 96–320 °K. The activation energies are determined by analyzing the glow peaks after thermal cleaning, using different methods. The results show that, in these phosphors, the electron traps responsible for thermoluminescence are present prior to irradiation. The infrared absorption spectra are recorded in the range of 4000-250 cm^-1. It is concluded that the traps are due to host lattice defects which may arise from S^-2 ion vacancies, created during phosphor preparation.     

Kinetics of luminescence as revealed from photo-, thermo- and electro-luminescence studies on CaS : Ag phosphors

Phosphorescence decay, thermoluminescence and electroluminescence of CaS : Ag phosphors prepared with a varying amount of silver as activator have been studied at room temperature, 301 K. The observations have been analysed to obtain the information about the type of kinetics involved in the luminescence process. In addition to this, the effect of the addition of an activator on the luminescence behaviour of the phosphors and on the distribution of trapping levels is discussed.     

Lu2SiO5:Ce透明薄膜改性及其发光性能

Lu2SiO5:Ce具有高密度、高光产额、快衰减等优点,是一种性能优异的新型X射线闪烁薄膜材料.本文采用溶胶-凝胶工艺和旋涂技术,以无机盐为原料、2-甲氧基乙醇为溶剂、聚乙二醇(PEG)为改性剂,在石英基片上成功制备出Lu2SiO5:Ce透明薄膜,较为详细地研究了PEG对该薄膜发光性能的影响.结果表明当采用浓度为12....     

Surface chemical changes of CaTiO3:Pr upon electron beam irradiation

Surface chemical changes of CaTiO₃:Pr³⁺ phosphor material and their effect on the red emission intensity of the ¹D₂→³H₄ transition of Pr³⁺, upon electron beam irradiation are presented. Red emission at 613 nm was obtained upon probing the surface with a 2 keV electron beam. The surface chemical changes and Pr³⁺ red emission were monitored using an Auger Electron Spectroscopy (AES) and Cathodoluminescence (CL) spectrometer, respectively. The CL intensity decreased with a decrease in O on the surface at 1×10⁻⁸ Torr base pressure and decreased with an increase in O on the surface at 1×10⁻⁶ Torr O₂. The X-ray Photoelectron Spectroscopy (XPS) revealed that CL degradation at 1×10⁻⁶ Torr O₂ is due to the formation of CaO and CaO_x as well as TiO₂/Ti₂O₃ non-luminescent species on the surface.     

Solvothermal synthesis and luminescence properties of the novel aluminum garnet phosphors for WLED applications

The color rendering index (CRI) and structural stability of cerium doped yttrium aluminum garnet (YAG:Ce) based phosphors have been enhanced by replacing Y³⁺ ions by larger radius ions (Tb³⁺, Gd³⁺, Eu³⁺, and Sm³⁺) at the dodecahedral site and replacing Al³⁺ ions by larger ones (Ga³⁺, Y³⁺, Tb³⁺, Gd³⁺, and Sm³⁺) at the octahedral site. These aluminum garnet crystalline powders were prepared by solvothermal reaction method at 300 °C for 48 h. The lattice constant values of synthetic aluminum garnet crystalline powders are larger than that of YAG and the emission wavelength of Ce³⁺ ion of these samples is longer than that of YAG:Ce. FESEM and TEM studies revealed that the Ln₃Ga₂Al₃O₁₂ and Ln₃Al₂Al₃O₁₂ crystalline powders have 3-dimensional star-like morphology with submicron size and good crystallinity, while, Ln₃(LnAl)Al₃O₁₂ garnet crystalline powders were cubic crystalline phases and shaped as cubes with the round edge having an approximate diameter of about 200–400 nm. All the prepared powders were grown along (100) direction and crystallized into single crystal. Also, the effects of treatment time and reaction temperature on the structure of aluminum garnet crystalline powders have been investigated.     

Energy transfer-based spectral properties of Tb-, Pr-, or Sm-codoped YAG:Ce nanocrystalline phosphors

Tb³⁺-, Pr³⁺-, or Sm³⁺-codoped YAG:Ce nanocrystalline phosphors were prepared using a modified polyol process. Possible tunability of Ce³⁺-related yellow emission in codoped YAG:Ce nanocrystalline systems was investigated. Dual emission of yellow and red spectral component with a single excitation wavelength was observed from YAG:Ce, Pr or YAG:Ce,Sm codoped systems via an energy transfer from Ce³⁺ and Pr³⁺ or Sm³⁺ ion. It was also observed that the energy transfer event in YAG:Ce, Pr nanocrystalline phosphor occurs mutually between Ce³⁺↔Pr³⁺, while in YAG:Ce, Sm and YAG:Ce, Tb the energy transfer progresses one way. The detailed pathways for transferring an excitation energy are explained based on the energy level diagrams of respective Ce³⁺, Pr³⁺, Sm³⁺, Tb³⁺ ion.     

Electron beam induced modification of poly(ethylene terephthalate) films

Electron beam processing of poly(ethylene terephthalate) (PET) films is found to promote significant changes in the melting heat, intrinsic viscosity and polymer film-liquid (water, isooctane and toluene) boundary surface tension. These properties are featured with several maximums depending on the absorbed dose and correlating with the modification of PET surface functionality. Studies using adsorption of acid-base indicators and IR-spectroscopy revealed that the increase of PET surface hydrophilicity is determined by the oxidation of methylene and methyne groups. Electron beam treatment of PET films on the surface of N-vinylpyrrolidone aqueous solution provided graft copolymerization with this comonomer at optimum process parameters (energy 700 keV, current 1 mA, absorbed dose 50 kGy).     

Blue luminescence of nanocrystalline CaZrO3:Tm phosphors synthesized by a modified Pechini sol-gel method

This paper reports the photoluminescence (PL) properties of nanocrystalline CaZrO₃:Tm phosphor synthesized by the polymerizable complex method based on the Pechini-type reaction. Nanosized phosphors with paving stone morphology were prepared at a relatively low temperature about 800 °C with the particle size being about 30 nm. The transmission electron microscope (TEM) images showed that further heat treatment at higher temperature could increase the particle size to 50 nm, but its morphology remained unchanged. The luminescence spectra indicated that the blue emission of CaZrO₃:Tm could be produced by four kinds of excitation energies, i.e. the charge transfer (CTS) between Tm³⁺-O²⁻, band-band absorption of host, the absorption defects in the host and the ³H₆-¹D₂ transition. The luminescent mechanism of CaZrO₃:Tm was deduced tentatively based on the luminescence spectra.     

Synthesis and optimum luminescence of monodispersed spheres for BaWO4-based green phosphors with doping of Tb

Monodispersed spheres for Tb³⁺-doped BaWO₄ (BWO:Tb) phosphors were prepared by a hydrothermal method. X-ray diffraction (XRD) and field-emission scanning electron microscopy were used to characterize the resulting samples. Emission and excitation spectra were studied using xenon excited spectroscopic experiments at room temperature. Because 12 at% BWO:Tb phosphor exhibits intensive green emission under 254 nm excitation in comparison with the commercial green fluorescent lamp phosphor (LaPO₄:Ce,Tb), it is considered to be a new promising green phosphor for fluorescent lamps application.     

Surface modifications of PADC polymeric material by ion beam bombardment for high technology applications

Surface modification of Poly (allyl diglycol carbonate) (PADC) is induced by 150 keV Ag ions of different fluences. The pristine as well as bombarded samples were investigated by UV–Vis spectroscopy, Fourier transform-infrared analysis (FTIR) and micro-hardness tester. The variations of wettability and surface free energy were determined by the contact angle measurements. The obtained results showed that ion beam bombardment induced increase in the absorption spectra of the UV–Vis with increase of ion fluence as well. The direct and indirect optical band gap decreased from 4.2 to 3.6 eV for pristine sample to 3.2 and 2.5 eV for those bombarded with Ag ion beam at the highest fluence, respectively. Changes in chemical properties were observed by Fourier transform infrared spectroscopy. Increase in the wettability, surface free energy and work of adhesion with increase the ion fluence were observed. Ion bombardment inducing increasing in a micro-hardness surface due to the high carbon surface concentration and cross-linking effects in the polymeric chains. The bombarded PADC surfaces may find special applications to the field of the micro-electronic devices and printing process.     

Degradation of Y2SiO5:Ce phosphor powders

The degradation of the cathodoluminescence (CL) intensity of cerium-doped yttrium silicate (Y₂SiO₅:Ce) phosphor powders was investigated for possible application in low voltage field emission displays (FEDs). Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of commercially available Y₂SiO₅:Ce phosphor powders. The degradation of the CL intensity for the powders is consistent with a well-known electron-stimulated surface chemical reaction (ESSCR) model. It was shown with XPS and CL that the electron stimulated reaction led to the formation of a luminescent silicon dioxide (SiO₂) layer on the surface of the Y₂SiO₅:Ce phosphor powder. XPS also indicated that the Ce concentration in the surface layer increased during the degradation process and the formation of CeO₂ and CeH₃ were also part of the degradation process. The CL intensity first decreased until about 300 C cm⁻² and then increased due to an extra peak arising at a wavelength of 650 nm.     

Enhanced luminescence of Ca3B2O6:Dy phosphors by Na-codoping for LED applications

The Ca_2.95−yDy_0.05B₂O₆:yNa⁺ (0≤y≤0.20) phosphors were synthesized at 1100 °C in air by the solid-state reaction route. The as-synthesized phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), photoluminescence excitation (PLE), photoluminescence (PL) spectra and thermoluminescence (TL) spectra. The PLE spectra show the excitation peaks from 300 to 400 nm due to the 4f-4f transitions of Dy³⁺. This mercury-free excitation is useful for solid-state lighting and light-emitting diodes (LEDs). The emission of Dy³⁺ ions on 350 nm excitation was observed at 480 nm (blue) due to the ⁴F_9/2→⁶H_15/2 transitions, 575 nm (yellow) due to ⁴F_9/2→⁶H_13/2 transitions and 660 nm (red) due to weak ⁴F_9/2→⁶H_11/2 emissions. The PL results from the investigated Ca_2.95−yDy_0.05B₂O₆:yNa⁺ phosphors show that Dy³⁺ emissions increase with the increase of the Na⁺ codoping ions. The integral intensity of yellow to blue (Y/B) can be tuned by controlling Na⁺ content. By the simulation of white light, the optimal CIE value (0.328, 0.334) can be achieved when the content of Na⁺-codoping ions is y=0.2. The results imply that the Ca_2.95−yDy_0.05B₂O₆:yNa⁺ phosphors could be potentially used as white LEDs.     

Study on relationship of luminescence in CaS:Eu,Sm and dopants concentration

In order to study different characteristic luminescence of Eu²⁺ and Sm³⁺, delayed photoluminescence (DPL) and infrared stimulated luminescence (ISL) spectra of CaS doped with europium and samarium have been investigated. The influence of Eu and Sm concentration on luminescence of Eu²⁺ in photoluminescence (PL) and ISL was respectively studied. It was found that, at low doping levels, PL emission intensity of Eu²⁺ increased linearly with increment of Eu, while decreased linearly with increment of Sm. However, further increment of Eu and Sm in CaS:Eu,Sm could not increase either the luminescent centres of Eu²⁺ or electron trapping sites of Sm³⁺. Different local environment of Eu²⁺ and Sm³⁺ in the lattice position is thought to be the cause of all observed luminescence phenomena. Finally, the maximum emission in ISL was obtained at 1000 ppm europium and 750 ppm samarium.     

The study on optically stimulated luminescence dosimeter based on the SrS：Eu,Sm and CaS：Eu,Sm

With the increasing use of nuclear energy, there is a need for a wider range of efficient dosimeters for radiation detection and assessment. There has been a tremendous growth in the development of radiation detectors and devices in the past few decades. In recent years, the development of new materials for radiation dosimetry has progressed significantly. Alkaline earth sulfides （AES） have been known for a long time as excellent and versatile phosphor materials. In the present investigation, a number of phosphor samples such as mono-, binary and ternary sulfides of alkaline earths （II^a-VI^b） have been prepared and their TL properties have been studied with respect to exposure （x-ray） response and fading. In this paper, some results on SrS：Eu, Sm and CaS：Eu, Sm phosphors are presented. A type of novel OSL dosimeter is described. The dosimeter takes advantage of the characteristics of charge trapping materials SrS：Eu, Sm and CaS：Eu, Sm that exhibit optically stimulated luminescence （OSL）. The measuring range of the dosimeter is from 0.01 to 1000 Gy. The OSL dosimeters provide capability for remote monitoring radiation locations which are difficult to access and hazardous. This equipment is relatively simple, small in size and has low power consumption. The device is suitable for space radiation dose exploration. In addition, it also can be used in IC and other radiation occasions and has good prospects.     

Integrated chemical process for exothermic wave synthesis of high luminance YAG:Ce phosphors

In this paper, high-luminance yellow-emitting Y₃Al₅O₁₂:Ce³⁺ phosphor (YAG:Ce) microparticles were prepared in a solid flame using a 1.425Y₂O₃+2.5Al₂O₃+0.15CeO₂+k(KClO₃+urea)+mNH₄F precursor mixture (here k is the number of moles of the KClO₃+urea red-ox mixture, and m is the number of moles of NH₄F). The self-sustaining combustion process for the entire reaction sample was provided by the heat generated from the KClO₃+urea mixture. Parametric studies demonstrated that the maximum temperature in the combustion wave varied from 885 to 1200 °C for k=2.0-3.0 mole and m=0-1.5 mole. X-ray analysis results showed that the product obtained in the solid flame consisted of Y₃Al₅O₁₂:Ce³⁺ and KCl phases. Therefore, after dissolving potassium chloride in distillated water, pure-phase YAG:Ce phosphor powder was obtained. The as-prepared YAG:Ce phosphor particles had diameters of 10-25 μm and good dispersity and exhibited luminescence properties comparable to those of YAG:Ce phosphor powders prepared by conventional high-temperature processing.     

NH4Cl作助熔剂合成CaS：Ce的光谱特性及其浓度效应

以ＮＨ４Ｃｌ作助溶剂，碳还原硫酸钙的方法合成了ＣａＳ：Ｃｅ。在紫外光激发下，ＣａＳ：Ｃｅ中存在着Ｃｅ＾３＋的＾２Ｄ－＾２Ｆ５／２（５００ｎｍ）和＾２Ｄ－＾２Ｆ７／２（５５０ｎｍ）跃迁发射，但在蓝色光激发下，只有波峰为５３２ｎｍ半宽度为９２ｎｍ的宽带发射。当Ｃｅ＾３＋的浓度为０．０７５ｍｏｌ％时，＾２Ｄ－＾２Ｆ５／２跃迁发射强度与＾２Ｄ－＾２Ｆ７／２跃迁发射强度相等，而５３２ｎｍ发射猝灭。     

Synthesis and luminescence properties of Tb:NaGd(WO4)2 novel green phosphors

Tb³⁺:NaGd(WO₄)₂ (Tb:NGW) phosphors with different Tb³⁺ concentrations have been synthesized by a mild hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence excitation and emission spectra and decay curve were used to characterize the Tb:NGW phosphors. XRD analysis confirmed the formation of NGW with scheelite structure. SEM study showed that the obtained Tb:NGW phosphors appeared to be nearly spherical and their sizes ranged from 1 to 1.5 μm. The excitation spectra of these systems showed an intense broad band with maximum at 270 nm related to the O→W ligand-to-metal charge-transfer state. Photoluminescence spectra indicated the phosphors emitted strong green light centered at 545 nm under UV light excitation. Analysis of the photoluminescence spectra with different Tb³⁺ concentrations revealed that the optimum dopant concentration for Tb³⁺ is about 15 at% of Tb³⁺ ions in Tb:NGW phosphors.