UV induced photoluminescence and thermally stimulated luminescence of ThO2:Tb3+ phosphor

Thorium oxide doped with trivalent terbium ions offers itself as a novel phosphor with its photo- and thermally-stimulated luminescence (PL and TSL) characteristics showing a marked change on sustained exposure to 254 and 365 nm ultraviolet (UV) radiation. The reduction in luminescence intensity of Tb³⁺ ions, on irradiation with 254 nm photons and subsequent restoration on exposure to 365 nm, has been correlated with the complimentary behaviour in UV-induced TSL. These changes are, in turn, ascribed to inter-configurational (f–d) transitions and e–h formation and recombination processes. UV radiation induced TSL output increases linearly with incident UV radiant energy at a constant radiation flux; however, for a fixed exposure, TSL output increases with increase in radiant flux.     

Synthesis of CaSO4:Dy,CaSO4:Eu3+ and CaSO4:Eu2+ phosphors

${\mathrm{CaSO}}_4:\mathrm{Dy}$ is a well-known phosphor for radiation dosimetry using thermoluminescence. ${\mathrm{CaSO}}_4:\mathrm{Eu}$, phosphors also find applications in radio-photoluminescence dosimetry and PLLCD. Various syntheses of these phosphors are described and optimum procedures are suggested. Effects of various preparation methods on luminescence characteristics are discussed in terms of elimination of unwanted impurities, grain size, etc.     

SrSO4:Eu磷光体的光释光特性

研究了通过掺杂得到的SrSO4:Eu(0.1mol%)的粉末样品的光释光(OSL)特性.用90Sr的β射线辐照0.116-1.16kGy后,测定了恒定光源激发的光释光发光曲线(CW-OSL)和线性光源激发的光释光发光曲线(LW-OSL),对发光曲线分析均得到了四种陷阱成分.采用复合作用响应函数得到SrSO4:Eu辐射剂量响应为线性-亚线性.测量了温度对OSL信号的影响,结果表明OSL信号的温度稳定性很好,最灵敏读出温度约为180℃,说明这时OSL信号来自热激发和光激发的共同作用.用60Coγ辐照100Gy后,测量了热释光(TL)三维光谱,确定了发光波长主要位于375nm,可以确定这是来自于Eu2+能级跃迁的发光.     

The photoluminescence,afterglow and up conversion photostimulated luminescence of Eu3+ doped Mg2SnO4 phosphors

The Mg₂SnO₄:Eu³⁺ phosphor with reddish photoluminescence, green afterglow and photostimulated luminescence is obtained by the solid state method. The host related afterglow is greatly enhanced by doping of Eu³⁺ and it can last nearly 6 h when the Eu³⁺ concentration is 1 mol%. The photostimulated luminescence is found to be weakened by doping of Eu³⁺. It was revealed that all the shallow traps and a part of the deep traps are involved in afterglow. The majority of deep traps are responsible for photostimulated luminescence. The impact of doping Eu³⁺ on the afterglow and photostimulated luminescence is investigated and we propose a feasible interpretation.     

SrSO4:Eu磷光体的光释光特性

研究了通过掺杂得到的SrSO4:Eu(01mol%)的粉末样品的光释光(OSL)特性.用90Sr的β射线辐照0116—116kGy后，测定了恒定光源激发的光释光发光曲线(CW-OSL)和线性光源激发的光释光发光曲线(LW-OSL)，对发光曲线分析均得到了四种陷阱成分.采用复合作用响应函数得到SrSO4:Eu辐射剂量响应为线性-亚线性.测量了温度对OSL信号的影响，结果表明OSL信号的温度稳定性很好，最灵敏读出温度约为180℃，说明这时OSL信号来自热激发和光激发的共同作用.用60Coγ辐照100Gy后，测量了热释光(TL)三维光谱，确定了发光波长主要位于375nm，可以确定这是来自于Eu2+能级跃迁的发光. 关键词： 光释光 热释光 SrSO4:Eu     

Persistent luminescence properties of SrMg2(PO4)2:Eu2+,Tb3+

We investigate the persistent luminescence in europium-doped SrMg₂(PO₄)₂ upon codoping with auxiliary terbium. Luminescence properties of the phosphors, including photoluminescence, luminescence decay and thermoluminescence, are systematically studied. SrMg₂(PO₄)₂:Eu²⁺ shows only a weak persistent luminescence, and codoping with Tb³⁺ is necessary to obtain considerable persistent luminescence. An energy level scheme is constructed to convey reasonable trapping and detrapping processes in the material.     

Effect of Eu3+ concentration on microstructure and photoluminescence of Sr2SiO4:Eu3+ phosphors prepared by microwave assisted sintering

In this paper, effect of Eu³⁺ doping concentrations on microstructure and photoluminescence of Sr₂SiO₄ phosphors was investigated. The Sr_2?xSiO₄:xEu³⁺ phosphors with x=0.05, 0.1, 0.2, 0.3 were synthesized by microwave assisted sintering at 1200 °C for 60 min in air. X-ray powder diffraction analysis confirmed the formation of pure Sr₂SiO₄ phase without second phase or phases of starting materials irrespective of the adding amount of Eu³⁺. From scanning electron microscopy image, it is found that with more Eu³⁺ ions introduced to Sr₂SiO₄, the shape of the particles is not much different from each other, but the particle size decreases significantly from 1 to 2 μm (when x=0.05) to less than 500 nm (when x=0.3). The emission spectrum was located obviously at 617 nm as the excitation spectrum at λ_ex=395 nm, and it had best emission intensity when x=0.1.     

Synthesis and luminescence properties of Eu3+,Bi3+-doped BaWO4 phosphors

BaWO₄:Eu³⁺,Bi³⁺ phosphors have been prepared by the conventional high-temperature solid-state reaction and chemical precipitation. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) technologies. When the phosphors are prepared by the high-temperature solidstate reaction, Bi³⁺ doping into BaWO₄:Eu³⁺ can increase the emission intensity of 613 nm. However, maximum emission at about 595 nm was observed in Eu³⁺,Bi³⁺-doped BaWO₄ phosphors prepared by the chemical precipitation. The decay constants (monitored at 595 and/or 613 nm) are within 45–100 s. The color purity of the Ba_0:865WO₄: Eu_0:11,Bi_0:025 phosphor (prepared by chemical precipitation) was 100%. The emission mechanism of Eu³⁺,Bi³⁺ in the BaWO₄ phosphors is briefly discussed.     

Preparation and photoluminescence properties of the Eu2+, Sm3+ co-doped Li2SrSiO4 phosphors

A series of Eu²⁺ and Sm³⁺ co-doped Li₂SrSiO₄ phosphors are prepared by the high temperature solid-state reaction. The morphology, structure and spectroscopic properties of the prepared samples are characterized by scanning electron microscopy, X-ray diffraction, diffuse reflection spectra, photoluminescence spectra and electron paramagnetic resonance spectra, respectively. The effect of Sm³⁺ doping concentration on the photoluminescence intensity of the prepared samples is also investigated. The results indicate that the crystal structure of Li₂SrSiO₄ is not changed with the Eu²⁺, Sm³⁺ co-doping. The spherical-like particle size of the obtained product is about 20–30 nm in diameter. When the Sm³⁺ concentration is 0.3 mol% and the Eu²⁺ concentration is 0.7 mol%, the phosphors show the maximum emission intensity, which is 50% higher than that of Eu²⁺ doped Li₂SrSiO₄. Excited at 420 nm, the phosphor presents a single broad emission band peaking at 558 nm, which is ascribed to the 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺ and ⁴G_5/2 → ⁶H_5/2 and ⁴G_5/2 → ⁶H_7/2 transitions of Sm³⁺. The Commission International de I′Eclairage chromaticity coordinates of Li₂SrSiO₄:0.7 mol% Eu²⁺, 0.3 mol% Sm³⁺ are x = 0.28, y = 0.28.     

Decay kinetics and thermally stimulated luminescence of Mn4+ in SrTiO3

Abstract

Decay kinetics of Mn⁴⁺ luminescence in SrTiO₃ and thermal stimulation of this luminescence (TSL) after low-temperature irradiation with light from the 355—520 nm region, have been investigated in the temperature range of 4.2—150K and 12—110K, respectively, for the first time. It is concluded that TSL glow peaks are associated with thermal release of carriers from shallow traps followed by Mn⁵⁺→Mn⁴⁺(²E) and/or Mn³⁺→Mn⁴⁺ (²E) charge transfer decay kinetics has been explained by considering trap energy levels taking part in the TSL process.     

High brightness and precise adjustment of multicolor-tunable luminescence of Lu2GeO5:Tb3+, Eu3+ phosphors for white LEDs

High brightness and precise adjustment of luminescence colour of phosphors are two main targets in the research of phosphor-converted white LEDs. However, few feasible strategy can be employed to achieve the multicolor-tunable luminescence under the premise of maintaining high quantum efficiency. Here, we demonstrate a high-efficiency energy-transfer process from Tb³⁺ to Eu³⁺ ions with a higher luminescent quantum efficiency (64.5% and 53.4%, respectively), and green-red multicolor emission in Lu₂GeO₅ host via varying the doping content of Tb³⁺ and Eu³⁺ ions. Besides, Lu₂GeO₅:Tb³⁺, Lu₂GeO₅: Eu³⁺ and Lu₂GeO₅: Tb³⁺, Eu³⁺ all exhibit weak thermal quenching which ensures the stable use of white LED device in the high temperature environment. This paper provides a novel multicolor-tunable phosphor with high brightness, efficient energy transfer and weak thermal quenching, which presents a potential application for UV-converted white LEDs.     

Li+共掺杂GdTaO4:Eu3+发光增强效应的研究

测量了不同浓度Li+共掺杂下GdTaO4:Eu3+荧光粉材料的X射线衍射谱(XRD)、发射光谱以及红外透射谱,并应用Judd-Ofelt理论,由发射光谱得到Eu3+的光谱跃迁强度参数Ω2.发现Li+共掺杂有助于提高GdTaO4:Eu3+的发光强度,当x=0.06和0.10时,612 nm处的发光强度分别被提升了1.7倍和1.5倍.发光增加的原因是因为Li+的助熔剂效应有效提高了GdTaO4材料的结品性能,并抑制了Cd2O3和Ta2O5杂相的产生,而非所推测的掺Li+引起了配位场对称性降低,从而导致宇称禁戒的放宽.此时Gd0.92-xLixTaO4:Eu3+0.08材料不仪结晶性能较好,而且Gd2O3和Ta2O5杂相也相对较少,故而发光增强最为明显.     

Solid state metathesis of CaSO4:Eu2+ phosphor

CaSO₄:Dy, is a well known phosphor for radiation dosimetry using thermoluminescence. CaSO₄:Eu³⁺ and CaSO₄:Eu²⁺ phosphors also find applications in radio-photoluminescence dosimetry and photoluminescent liquid crystal displays (PLLCD), respectively. Various syntheses of these phosphors are known. In this paper solid state metathesis of CaSO₄:Eu using domestic microwave oven is described for the first time. The synthesis is fast, the entire process being completed within few minutes. The phosphor is characterized using XRD and PL techniques.     

Resonant processes causing photon multiplication in CaSO4:Tb3+

The emission spectra of single and polyterbium centers have been measured at the excitation of CaSO₄:Tb³⁺ phosphors with different charge compensators (Na⁺, calcium vacancies, etc.) by 3.8–35 eV photons or 5 and 300 keV electrons at 6–300 K. The possible mechanisms providing quantum yield above unity for green (⁵D₄ → ⁷F_J) and blue emission (⁵D₃ → ⁷F_J) of Tb³⁺ at the direct intracenter excitation, excitation of oxyanions or creation of hot (nonrelaxed) electrons and holes have been discussed. On the basis of thermally stimulated luminescence at 6–600 K, the peculiarities of the hopping diffusion of relaxed electrons and holes and their tentative low-temperature self-trapping have been considered.     

Na2GdPO4F2:Tb3+绿色荧光粉阴极射线发光研究

通过高温固相法制备Na2GdPO4F2:Tb3+绿色荧光粉,并利用X射线粉末衍射(XRD)和阴极射线光谱分别对其物相、阴极射线发光性能进行研究.结果表明,Tb3+作为绿色发光中心进入到Na2Gd2PO4F2的晶格中取代Gd3+的格位,在低电子束(0.5～5 kV)激发下主要表现出Tb3+的特征跃迁(5D3.4→7FJ,J=6～2),其中以5D4→7F5跃迁(546 nn)为主.样品Na2Gd0.95Tb0.05PO4F2在阴极射线激发下的色坐标为(0.240 3,0.438 6).随着电压、电流和掺杂量的增加,荧光粉的发光强度逐渐提高,其中,最佳的样品为Na2Gd0.9Tb0.1PO4F2.     

Eu/Tb ions co-doped white light luminescence Y2O3 phosphors

Y₂O₃:Eu³⁺, Tb³⁺ phosphors with white emission are prepared with different doping concentration of Eu³⁺ and Tb³⁺ ions and synthesizing temperatures from 750 to 950 °C by the co-precipitation method. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the crystallinity of the synthesized samples increases with enhancing the firing temperature. The photoluminescence spectra indicate the Eu³⁺ and Tb³⁺ co-doped Y₂O₃ phosphors show five main emission peaks: three at 590, 611 and 629 nm originate from Eu³⁺ and two at 481 and 541 nm originate from Tb³⁺, under excitation of 250-320 nm irradition. The white light luminescence color could be changed by varying the excitation wavelength. Different concentrations of Eu³⁺ and Tb³⁺ ions were induced into the Y₂O₃ lattice and the energy transfer from Tb³⁺→Eu³⁺ ions in these phosphors was found. The Commission International de l’Eclairage (CIE) chromaticity shows that the Y₂O₃:Eu³⁺, Tb³⁺ phosphors can obtain an intense white emission.     

Mechanoluminescence,thermoluminescence and photoluminescence studies on Al2O3:Tb phosphors

Terbium activated Al₂O₃ phosphors were synthesized by combustion technique using hydrazine as a reductive non-carbonaceous fuel. X-ray diffraction (XRD) patterns of the samples were recorded to confirm the formation of the sample. Scanning electron microscope (SEM) images were taken to study the surface morphology of the sample. The photoluminescence (PL), thermoluminescence (TL) and mechanoluminescence (ML) properties of the γ-ray irradiated samples were studied. ML was excited impulsively by dropping a piston on the sample. In ML glow curves one peak with a shoulder was observed. ML intensity increases with activator concentration. Optimum ML was observed for the sample having 0.5 mol% of Tb ions. In the TL glow curve two distinct peaks, one around 222 °C and another around 280 °C, were observed for the samples having 0.5 mol% of activator concentration. In the PL spectra the ⁵D₄→⁷F₅ line at 544 nm in the green region is observed, which is the strongest in Al₂O₃ system. It is suggested that de-trapping of trapped charge carriers followed by recombination is responsible for ML and TL in this system.     

Radical-recombination luminescence,ion-luminescence and photoluminescence of CaGa2S4:Eu

CaGa₂S₄ based luminophors have recently attracted significant attention due to their high efficiency. Very little is known now about the surface and near surface luminescence of these luminophors. The ion-luminescence of CaGa₂S₄:Eu excited by low energy hydrogen ions (up to 3 keV) and the radical-recombination luminescence excited by neutral hydrogen atoms of thermal energies have been studied. The latter is due to chemical energy released at the surface during heterogeneous recombination of atoms into molecules (∼4 eV per recombination event). The radical-recombination luminescence is likely the most surface kind of luminescence, while the ion-luminescence is the luminescence of near-surface layers. In this regard the photoluminescence is the bulk one of with which the characteristics of the surface luminescence might be compared.