Photoluminescence properties of MgAl2O4:Dy powder phosphor

Trivalent dysprosium (Dy³⁺) activated magnesium alluminate phosphors were synthesized by high temperature solid state reaction method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting phosphors. The results show that the obtained MgAl₂O₄:Dy³⁺ phosphors have good crystallinity, spherical morphology with sizes ranged from 120 to 140 nm and strong blue emission under an excitation of 258 nm. The emission spectrum of this phosphor consists of two emission bands: blue band and yellow band, and the emission intensity of the former is stronger than that of the later. Luminescence quenching is explained and the corresponding luminescence mechanisms have been proposed.     

CaMoO4:x%Yb3+: a novel near-infrared quantum-cutting phosphors via cooperative energy transfer

An efficient near-infrared (NIR) dowmconversion (DC) has been demonstrated in the CaMoO4:Yb3+ phosphors. Very strong NIR emission around 998 nm from the 2F(7/2) --> 2F(5/2) transition of the Yb3+ has been observed under ultraviolet excitation. A similar broad excitation band due to the absorption of the host CaMoO4 has been recorded when the NIR emission of Yb3+ and the visible molybdate (MoO4(-2)) emission are monitored, which suggests an efficient energy transfer (ET) from the host to the Yb3+. The Yb3+ concentration-dependent luminescence properties and lifetimes of both the visible and NIR emissions have also been studied. The lifetime of the molybdate emission decreases rapidly with the increasing Yb3+ concentration, further verifying the efficient ET from the host to the Yb3+. Moreover, the low temperature measurements have also been carried out to investigate the ET mechanism in the phosphors. A cooperative energy transfer (CET) mechanism has been proposed to rationalize the DC effect. The newly studied CaMoO4:Yb3+ DC phosphors, which can convert the broadband emission of the MoO4(2-) into NIR emission of Yb3+ with a twofold increase in the photon number will have potential application in greatly enhancing the response of silicon-based solar cells with a relatively higher Yb3+ quenching concentration.     

High-energy emission band nature in ZnS-type phosphors activated with silver and chlorine

The cathodoluminescence emission spectra of cubic blue-emitting ZnS:Ag, Cl, hexagonal green-emitting (Zn_0.675, Cd_0.325) S:Ag, Cl as well as hexagonal red-emitting (Zn_0.27, Cd_0.73) S:Ag, Cl phosphors have been measured at 293, 77 and 4.2 K. The measured spectra of the phosphors exhibited a single broad emission band at 293 K, while they had two emission bands at 77 and 4.2 K. The two emission bands shifted to a lower energy with increase of their corresponding half-widths as the temperature at which the spectra were measured was raised. The time-resolved emission spectra measured showed that the low-energy band also shifted in the lower energy direction during the decay of luminescence, confirming its donor-acceptor (DA) transition nature. The high-energy band decayed faster than the low-energy one and no energy shift occurred during its decay; it was attributed to donor-isoelectronic pair (DI) transition. The lifetimes of 0.625 and 4.2 µsec were estimated for high- and low-energy bands, respectively, in the emission spectra of ZnS:Ag, Cl at 4.2 K.     

Effect of shock wave processing on the properties of ZnS and ZnS-based phosphors

This paper describes a process for shock wave processing of ZnS powder in a closed protective metallic ampule wrapped in an explosive sheet, which is exploded to generate a shock wave. The process enables control over the shock wave energy delivered to ZnS. The method is used for ZnS preprocessing in the synthesis of zinc sulfide phosphors. The effect of shock wave processing on the particle size and crystal structure of ZnS is examined. The processing conditions are optimized so as to increase the brightness of the phosphors fabricated from the zinc sulfide.     

Luminescence properties of nano-crystalline Ba3MgSi2O8:Eu2+, Mn2+ phosphors

Ba3MgSi2O8:Eu2+, Mn2+ phosphors were synthesized by the sol-gel method and high temperature solid-state reaction method, respectively. XRD (X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy), PL (photoluminescence spectra), and PLE (photoluminescence excitation spectra) were measured to characterize the samples. Emission and excitation spectra of our Ba3MgSi2O8:Eu2+, Mn2+ phosphors monitored at 441, 515, and 614 nm are depicted in the paper. The emission intensities of 441 and 515 nm emission bands increase with increasing Eu2+ concentration, while the peak intensity of the 614 nm band increases with increasing Mn2+ concentration. We conclude that the 515 nm emission band is attributed to the 4f(6)5d transition of Eu2+ ions substituted by Ba2+ sites in Ba2SiO4. The 441 nm emission band originates from Eu2+ ions, while the 614 nm emission band originates from Mn2+ ions of Ba3MgSi2O8:Eu2+, Mn2+. Nano-crystalline Ba3MgSi2O8:Eu2+, Mn2+ phosphors prepared by the sol-gel method show higher color rendering and better color temperature in comparison with the samples prepared by high temperature solid-state reaction method.     

NIR to VIS frequency upconversion luminescence properties of Er-doped YPO4 phosphors

Different concentrations of Er³⁺-doped YPO₄:Er powder phosphors have been synthesized by the conventional solid state reaction method and are characterized by X-ray diffraction (XRD), field emission scanning electronic microscopy (FESEM), and upconversion emission measurements. An intense red emission band and a weak green emission band are observed under NIR excitation at 975 nm in case of samples with high dopant concentration while no upconversion emission was observed at lower Er³⁺ ion concentrations. The possible mechanisms involved in the upconversion process have been discussed in comparison to results with similar reported works.     

等离子体平板显示用发光材料

本文介绍了ＰＤＰ用荧光粉的基本情况及其应用特性。归纳出基团敏化带位置的一般规律及阳离子对基团敏化带波长位移的影响，并指出，提高发光效率，改善荧光粉的热稳定性和辐照稳定性，开发新型稀灾粉等具有重要意义。     

Photomagnetic susceptibility effect in CaSo4: Dy phosphors

Dysprosium activated phosphors of diverse activator concentration have been prepared, with and without addition of flux and their magnetic susceptibilities have been measured by Gouy method. The changes in magnetic susceptibilities have been observed for both with and without flux added phosphors and both in presence and absence of light as well. The observed decrease of magnetic susceptibility has been attributed to the difference in multiplicities of emitting and ground state of Dy³⁺. The increase in magnetic susceptibility in flux added samples has been attributed to the increased population of impurity ions (Dy³⁺), in the host lattice, due to the presence of flux.     

UV luminescence of commercial YAG:Ce phosphors

It is established that the emission spectrum of synthesized YAG:Ce phosphors excited at a wave-length of 290 nm contains, in addition to a yellow-green band, two intense UV bands with maxima at ～320 and ～360 nm. The observed separation of these emission bands is related to the partial absorption of radiation by Ce³⁺ ions. Nonreabsorbed UV luminescence spectra have been measured and characterized.     

Monodisperse colloidal spheres for (Y,Eu)2O3 red-emitting phosphors: establishment of processing window and size-dependent luminescence behavior

Abstract

The urea-based homogeneous precipitation method was introduced in the preparation of monodisperse colloidal spheres for (Y_0.95Eu_0.05)₂O₃ red-emitting phosphors, and the processing window was defined. Particle size and shape are significantly affected by the ion concentration and the urea/RE³⁺ molar ratio R (RE³⁺=Y³⁺+Eu³⁺). A low ion concentration is beneficial in forming monodisperse spheres and extending their formation domain. Increasing R results in a gradual change in the composition of spherical particles from the core-shell Eu(OH)CO₃@Y(OH)CO₃ structure to a homogeneous solid solution, thereby significantly lowering the calcination temperature at which precursors convert to oxides. Upon UV excitation into the charge-transfer band at 254 nm, the uniform phosphor spheres of (Y_0.95Eu_0.05)₂O₃ exhibit typical red emissions at 613 nm; the emission is stronger from larger particles mainly because of their smaller surface area. Both the luminescence intensity and quantum efficiency of the oxide phosphors increase with elevated calcination temperatures. The spherical shape and excellent dispersion of the precursor particles (～450 nm in diameter) have been well retained after calcination at 1000 ^○C for 4 h, and the resultant oxide phosphors exhibit external and internal quantum efficiencies of 50 and 82%, respectively.     

Temperature-Dependent Luminescence Characteristic of SrSi2O2N2：Eu2＋ Phosphor and Its Thermal Quenching Behavior

The yellow SrSi2O2N2：Eu2＋ phosphor has been synthesized by using a simple solid-state reaction method with Sr2SiO4：Eu2＋ as the precursor. It shows a broad excitation band extending from 250 to 520 nm and an asymmetric emission band with a main peak at about 550 nm. The emission intensity of the SrSi202N2：Eu2＋ is about 1.2 times higher than the commercial yellow phosphor YAG：Ce3＋ （P46-Y3）. The temperature- dependent luminescence characteristic of SrSi202N2：Eu2＋ has been investigated in this paper. With increasing temperature, the emission band of SrSi202N2：Eu2＋ shows anomalous blue-shift along with decreasing emission intensity and the broadening full width at half maximum （FWHM）. Particularly, compared with YAG：Ce3＋ （P46-Y3）, the yellow SrSi202N2：Eu2＋ phosphors exhibit higher thermal stability due to their weaker electron-phonon coupling strength （1.1）, lower stokes shift （0.0576 eV） and larger activation energy （0.288 eV）. All these results indicate that SrSi202N2：Eu2＋ yellow phosphors have potential application for white light-emitting diodes （LEDs）, What＇s more, an energy level scheme is constructed to explain the anomalous blue-shift phenomenon.     

Advances in sulfide phosphors for displays and lighting

For traditional applications such as cathode ray tubes and fluorescent lamps, many inorganic phosphors have been optimised during decades. For new applications in display and lighting technology, novel materials are being developed. After giving a short history of sulfide phosphors, the present paper will focus on Ca_1−x Sr _x S:Eu single crystal particle phosphors. The material is grown by solvothermal synthesis, process not needing toxic gases or high temperature processing steps. This phosphor combines a broad excitation spectrum and a broad—saturated red—emission spectrum, which makes it an ideal material for wavelength conversion in LEDs for general lighting.     

Analysis of change in microstructure and properties during high temperature processing of ultralow C and high Nb microalloyed steel

Abstract

To further improve the strength and toughness, the advanced thermomechanical controlled processing has been applied in the development of an ultralow C and high Nb bearing steel. In the present investigation, the effects of processing parameters, consisting of the coiling and starting temperatures in non-recrystallisation region, on the final microstructure and mechanical properties of this steel have been studied by tensile, Charpy impact tests, optical microscopy and transmission electron microscopy. Results indicate that the acicular ferrite dominated microstructure can be greatly refined in grain size with decreasing the starting temperature of finishing rolling. However, for high Nb steels, the too low starting temperature would promote the formation of high temperature transformation products and consequently make against the improvement of mechanical properties. In addition, the optimum temperature window of finishing rolling is found to be also related to alloying levels of austenite stabilising elements. At the high starting temperature of finishing rolling, the precipitation strength contribution increases with increasing coiling temperature. However, the increase in strain accumulation associated with low temperature processing greatly reduces the sensitivity of the precipitation strength contribution to coiling temperature.     

反应性钌(Ⅱ)-二亚胺类荧光指示剂的研究进展

为防止氧敏感荧光膜中荧光指示剂的流失,人们在荧光指示剂中引入反应性官能团,使指示剂分子化学键合到基材表面。概述了反应性钌(Ⅱ)-二亚胺络合物荧光指示剂的研究进展,包括反应性联吡啶、反应性邻菲咯啉配体的合成,反应性钌(Ⅱ)-二亚胺荧光指示剂的合成及其荧光特性。介绍了反应性钌(Ⅱ)-二亚胺类荧光指示剂在溶氧传感器中的应用研究。     

Enhanced photoluminescence decay processes of doped CaS phosphors at low temperature

CaS phosphor samples singly doped with Mn impurity and doubly doped with Mn and X (X=?Fe, Co and Ni) have been synthesized using a flux method. Crystal structure and phase identification of doped CaS phosphors have been carried out by X-ray diffraction (XRD) studies. A pulse excitation method has been employed to study the optical parameters of the doped phosphors. Excited state lifetime measurements at liquid nitrogen temperature were carried out with a pulsed UV laser (nitrogen laser) as the excitation source has a short pulse width (10?ns) and high peak power (200?kW per pulse). The results have been compared with room temperature lifetime studies. Enhancement in photoluminescence intensity and lifetime shortening in these synthesized doped phosphors is reported at low temperature. The lifetime values have been found to be in the microsecond time domain for CaS:Mn phosphors while on addition of a quencher impurity Ni to CaS:Mn phosphors, the lifetime values reduce to the nanosecond time domain at 77?K temperature. A thermally activated carrier transfer model has been proposed to explain the observed abnormal temperature behaviour of emission from CaS:Mn, X-doped phosphors.     

Silicon-based oxynitride and nitride phosphors for white LEDs—A review

As a novel class of inorganic phosphors, oxynitride and nitride luminescent materials have received considerable attention because of their potential applications in solid-state lightings and displays. In this review we focus on recent developments in the preparation, crystal structure, luminescence and applications of silicon-based oxynitride and nitride phosphors for white light-emitting diodes (LEDs). The structures of silicon-based oxynitrides and nitrides (i.e., nitridosilicates, nitridoaluminosilicates, oxonitridosilicates, oxonitridoaluminosilicates, and sialons) are generally built up of networks of crosslinking SiN₄ tetrahedra. This is anticipated to significantly lower the excited state of the 5d electrons of doped rare-earth elements due to large crystal-field splitting and a strong nephelauxetic effect. This enables the silicon-based oxynitride and nitride phosphors to have a broad excitation band extending from the ultraviolet to visible-light range, and thus strongly absorb blue-to-green light. The structural versatility of oxynitride and nitride phosphors makes it possible to attain all the emission colors of blue, green, yellow, and red; thus, they are suitable for use in white LEDs. This novel class of phosphors has demonstrated its superior suitability for use in white LEDs and can be used in bichromatic or multichromatic LEDs with excellent properties of high luminous efficacy, high chromatic stability, a wide range of white light with adjustable correlated color temperatures (CCTs), and brilliant color-rendering properties.     

Silicon-based oxynitride and nitride phosphors for white LEDs—A review

As a novel class of inorganic phosphors, oxynitride and nitride luminescent materials have received considerable attention because of their potential applications in solid-state lightings and displays. In this review we focus on recent developments in the preparation, crystal structure, luminescence and applications of silicon-based oxynitride and nitride phosphors for white light-emitting diodes (LEDs). The structures of silicon-based oxynitrides and nitrides (i.e., nitridosilicates, nitridoaluminosilicates, oxonitridosilicates, oxonitridoaluminosilicates, and sialons) are generally built up of networks of crosslinking SiN₄ tetrahedra. This is anticipated to significantly lower the excited state of the 5d electrons of doped rare-earth elements due to large crystal-field splitting and a strong nephelauxetic effect. This enables the silicon-based oxynitride and nitride phosphors to have a broad excitation band extending from the ultraviolet to visible-light range, and thus strongly absorb blue-to-green light. The structural versatility of oxynitride and nitride phosphors makes it possible to attain all the emission colors of blue, green, yellow, and red; thus, they are suitable for use in white LEDs. This novel class of phosphors has demonstrated its superior suitability for use in white LEDs and can be used in bichromatic or multichromatic LEDs with excellent properties of high luminous efficacy, high chromatic stability, a wide range of white light with adjustable correlated color temperatures (CCTs), and brilliant color-rendering properties.     

Facile synthesis of BaMoO4 and BaMoO4/BaWO4 heterostructures with type -I band arrangement and enhanced photoluminescence properties

A series of BaMoO₄ and BaMoO₄/BaWO₄ phosphors were successfully prepared via a polyacrylamide gel method and low temperature calcination technology. The effects of sintering temperature and mass percentage of BaMoO₄/BaWO₄ on the phase purity, functional group, surface morphology, charge state, photoluminescence properties and photocatalytic activity of the prepared products were studied in detail. The results indicate that the BaMoO₄ phosphor is a scheelite tetragonal structure with high crystallinity. The photoluminescence spectra indicates that the phosphors have a strong blue emission peak at 440 nm with excitation wavelength of 282 nm for the BaMoO₄ phosphor, and three emission peaks at 400, 440 and 460 nm with excitation wavelength of 284 nm for the BaMoO₄/BaWO₄ phosphors. These photoluminescence behaviors can be ascribed to the ¹T₂→¹A₁ transition, Jahn–Teller distorted tetrahedral symmetry of [MoO₄]^2- and surface defect. Photocatalytic experiments further confirmed that the BaMoO₄/BaWO₄ phosphors exhibit a high recombination rate of electron hole pairs. The result further indicates that the type-I band arrangement structure of BaMoO₄/BaWO₄ phosphors is beneficial to enhance the photoluminescent properties of single-phase phosphors. This study provides a novel route for preparing the type-I band arrangement structure composite phosphors with high photoluminescent properties and potential applications in light emitting devices, optoelectronic devices, laser devices and white pigments.     

Fine yellow α-SiAlON:Eu phosphors for white LEDs prepared by the gas-reduction–nitridation method

Yellow-emitting a-SiAlON:Eu²⁺ phosphors were synthesized by the gas reduction and nitridation of a homogeneous oxide precursor in a CaO–Al₂O₃–SiO₂–Eu₂O₃ system at 1400–1450 °C using an NH₃–CH₄ mixture gas as a reduction–nitridation agent. The precursor was prepared by a sol–gel process using a low-cost nitrate, tetraethyl orthosilicate and citric acid as the starting materials. The effects of reaction parameters such as heating rate, temperature, holding time and CH₄ content on the composition, microstructure and photoluminescence of the prepared powders were investigated. Nearly single-phase α-SiAlON was successfully synthesized by the one-step gas reduction and nitridation without the need for post-annealing at a higher temperature. The prepared powders consisted of relatively well-dispersed and uniform crystals with a hexagonal shape. The photoluminescence spectra of Eu-doped Ca-α-SiAlON phosphors excited by near-ultraviolet or blue light showed a broad, yellow emission band at 500–700 nm, which agrees well with that obtained from phosphors prepared by the conventional solid-state reaction.     

稀土掺杂双钙钛矿结构红色荧光粉的制备及其发光性能

采用高温固相反应法制备了Sr_(2-x)BaxMgMoO_6∶Eu~(3+)(x=0~1)双钙钛矿结构红色荧光粉。探讨了预处理及煅烧制度、Ba取代量对Sr_(2-x)BaxMgMoO_6∶Eu~(3+)荧光粉的相结构和发光性能的影响。Sr_2Mg_(0.94)Eu_(0.06)MoO_6荧光粉最佳制备工艺为:在700℃下预处理1h再升温至1050℃预处理1h并随炉降温后研细,再在1300℃煅烧4h,所得样品主相为双钙钛矿结构的Sr2MgMoO6四方相。其最强发光峰位于617nm附近,对应于Eu3+的5D0→7F2电偶极跃迁。随着Ba2+对Sr2+的取代量的增加晶体对称性提高,晶体结构由四方相变为立方相,样品的激发峰强度显著提高。由于晶体对称性的提高,抑制了荧光粉在617nm处5D0→7F2红光发射,其发光由电偶极跃迁占主导转变为磁偶极跃迁占主导。