Energy transfer and radiative recombination processes in (Gd, Lu)3Ga3Al2O12:Pr3+ scintillators

(Gd_xLu_3−x)Ga₃Al₂O₁₂:0.3 at.%Pr (x = 0.025, 0.05, 0.1, 0.2, 0.4, 0.6) (GLGAG:Pr) polycrystalline powders are prepared by solid-state reaction method. To better understand the luminescence mechanism, the optical diffuse reflectance, photoluminescence emission and excitation, X-ray excited luminescence spectra and decay kinetics of GLGAG:Pr were investigated in detailed, allowing the determination of energy transfer from 5d state of Pr³⁺ to 4f state of Gd³⁺, and the non-radiative relaxation from 5d to 4f state of Pr³⁺. Besides, the former process plays more negative role in the emission quenching of GLGAG:Pr than later one. Pr³⁺ ion is regarded as an ineffective activation ion in Gd-based multicomponent aluminate garnets. In addition, the wavelength-resolved thermoluminescence spectra of GLGAG:Pr were studied after UV and X-ray irradiation. It is revealed that the localized recombination processes from electron traps to lower lying 4f levels of Pr³⁺ occurs without populating the higher 5d levels of Pr³⁺.     

Dy~(3+)/Tb~(3+)掺杂高钆镥闪烁玻璃光谱性能

用高温熔融法制备了Dy3+/Tb3+掺杂的高钆镥氟氧化物闪烁玻璃样品,测试分析了其吸收光谱、激发与发射光谱及衰减曲线等。研究了Dy3+和Tb3+离子浓度增加对Tb3+离子发光的影响以及Dy3+离子的浓度猝灭效应;通过IH理论模型分析了Dy3+和Tb3+离子的能量传递方式和能量传递效率。结果表明Dy3+离子对Tb3+离子发光具有敏化作用,随着Dy3+离子浓度增加敏化作用增强,但是当Dy3+离子的浓度达到2%(摩尔分数)以上时,随着Dy3+离子浓度的增加,Tb3+离子的发光强度降低;Dy3+和Tb3+离子的能量传递方式为无辐射能量传递方式,且能量传递效率可以达到60%以上。     

Luminescence properties and energy transfer studies of a color tunable BaY2Si3O10:Tm3+,Dy3+ phosphor

A series of color-tunable and white light emitting phosphors BaY₂Si₃O₁₀:Tm³⁺,Dy³⁺ were synthesized by a high temperature solid-state reaction, and their phase structure, photoluminescence properties, and energy transfer processes between rare-earth ions were investigated in detail. Upon UV excitation, white light emission depending on dopant concentrations could be achieved by integrating a blue emission band located at 458 nm and an orange one located at 576 nm attributed to Tm³⁺ and Dy³⁺ ions, respectively. In addition, the energy transfer process between Tm³⁺ and Dy³⁺ ions was demonstrated to be a resonant type via a dipole–quadrupole mechanism. Preliminary studies showed that the phosphor might be promising as a single-phased white-light-emitting phosphor for UV chip pumped white-light LEDs.     

Co-existence phenomenon of Ce3+/Ce4+ and Tb3+ in Ce/Tb co-doped Zn2(BO3)(OH)0.75F0.25 phosphor: Luminescence and energy transfer

A serials of Zn₂(BO₃)(OH)_0.75F_0.25 (ZBF), Tb³⁺, Ce^3+/4+ single-doped ZBF and Tb³⁺/Ce^3+/4+ co-doped ZBF novel phosphors with belt-like morphology were obtained through hydrothermal reaction without any surfactant. The obtained samples were characterized by XRD, SEM, EDS, TEM, TGA, XPS, DR, PL, and DT. The TGA curve shows that the phosphor is thermal stability. XPS results show that Tb³⁺ is present in the Tb-doped phosphor, and the Ce³⁺/Ce⁴⁺ mixed valence is present in the Ce-doped phosphor. The PL results indicate that ZBF host material and ZBH:Ce^3+/4+ can emit blue light, ZBF:Tb³⁺ can emit green light. Compared with the Tb³⁺ single doped phosphor, the Tb³⁺/Ce^3+/4+ co-doped phosphors shown stronger emission and shorter decay time, which is attributed to the effective energy transfer from the Ce^3+/4+ to Tb³⁺ ions.     

Single-component and white light-emitting phosphor BaAl2Si2O8: Dy3+, Eu3+ synthesis,luminescence, energy transfer,and tunable color

A series of Dy³⁺ - Eu³⁺ co-doped BaAl₂Si₂O₈ phosphors were prepared via the conventional solid-state reaction method. Their crystal structure, luminescent characteristic and lifetime were investigated. The optimum doping concentrations of Dy³⁺and Eu³⁺ are both 0.05 for Dy³⁺ or Eu³⁺ singly doped BaAl₂Si₂O₈. Furthermore, BaAl₂Si₂O₈: 0.05Dy³⁺ and BaAl₂Si₂O₈: 0.05Eu³⁺ emits yellow and red light. The emission color of BaAl₂Si₂O₈: Dy³⁺, Eu³⁺ could be tuned from yellow to white due to the energy transfer. This energy transfer from Dy³⁺ to Eu³⁺ was confirmed and investigated by photoluminescence spectra and the decay time of energy donor Dy³⁺ ions. With constantly increasing Eu³⁺ concentration, the energy transfer efficiency from Dy³⁺ to Eu³⁺ in BaAl₂Si₂O₈ host increased gradually and reached as high as 81%, the quantum yield was about 47.43%. BaAl₂Si₂O₈: Dy³⁺, Eu³⁺ phosphors can be effectively excited by UV (about 348 nm) light and emit visible light from yellow to white by altering the concentration ratio of Dy³⁺ and Eu³⁺, indicating that the phosphors have potential applications as a white light-emitting phosphor for display and lighting.     

Spectral analysis of RE (RE = Sm, Dy, and Tm): P2O5–Al2O3–Na2O glasses

Phosphate glasses in the compositions of 70P₂O₅–15Al₂O₃–14Na₂O–1RE³⁺ (RE = Sm, Dy, and Tm) (mol%) were prepared by melt-quenching technique and characterized optically. The differential thermal analysis (DTA) profile of the host glass was carried out to confirm its thermal stability. For all the glasses absorption, photoluminescence and decay measurements have also been carried out. These glasses have shown strong emission and absorption bands in visible and near-infrared (NIR) region. From the measured absorption spectra, Judd–Ofelt (J–O) intensity parameters (Ω₂, Ω₄ and Ω₆) have been calculated for all the studied ions. For Sm³⁺ doped glass, four emission bands centered at 562 nm (⁴G_5/2 → ⁶H_5/2), 598 nm (⁴G_5/2 → ⁶H_7/2), 644 nm (⁴G_5/2 → ⁶H_9/2), and 704 nm (⁴G_5/2 → ⁶H_11/2) have been observed with 402 nm (⁶H_5/2 → ⁴F_7/2) excitation wavelength. Of them, 598 nm (⁴G_5/2 → ⁶H_7/2) has shown a bright orange emission. With regard to Dy³⁺ doped glass, a blue emission band centered at 486 nm (⁴F_9/2 → ⁶H_15/2) and a bright yellow emission at 575 nm (⁴F_9/2 → ⁶H_13/2) have been observed, apart from 662 nm (⁴F_9/2 → ⁶H_11/2) emission transition with an excitation at 388 nm (⁶H_15/2 → ⁴I_13/2,⁴F_7/2) wavelength. Emission bands of 650 nm (¹G₄ → ³F₄) and 785 nm (¹G₄ → ³H₅) transitions for the Tm³⁺ doped glass, with an excitation wavelength at 466 nm (³H₆ → ¹G₄), have also been observed. The stimulated emission cross-sections of all the emission bands of RE³⁺ glasses (RE = Sm, Dy, and Tm) have been computed based on their measured full-width at half maximum (FWHM, Δλ) and measured lifetimes (τ_m).     

Photoluminescence mechanisms of color-tunable Sr2CeO4: Eu3+, Dy3+ phosphors based on experimental and first-principles investigation

We report single-phased color-tunable phosphors (Sr₂CeO₄: Eu³⁺, Dy³⁺) synthesized by a polymer-network gel method for UV–LED. The photoluminescence properties and possible energy transfer mechanisms of Eu³⁺ and Dy³⁺ in Sr₂CeO₄ were investigated by experiments and first principles calculations. The results show that the ⁵D₀ → ⁷F₂ emission of Eu³⁺ is enhanced by the increase in the amount of Eu³⁺ ions and Eu³⁺ substitution makes more stable defect than Dy³⁺ substitution does. The photoluminescence mechanism of Sr_1.994−xEu_xDy_0.006CeO₄ can be explained by the energy transfer model with the consideration of the defect conditions in the crystals.     

(La,Dy)2W2O9 tungstates: Selected synthesis,enhanced luminescence through Gd3+ co-doping,and favorable quantum efficiency

In this study, a series of well dispersed (La_1-xDy_x)₂W₂O₉ and (La_0.98-yGd_yDy_0.02)₂W₂O₉ phosphors were selected synthesized by co-precipitation and subsequent calcination, where the effects of RE³⁺:WO₄^2- molar ratio and solution pH were investigated. The triclinic (La_1-xDy_x)₂W₂O₉ exhibited a series of sharp emission peaks assigned to ⁴F_9/2→⁶H_15/2, ⁶H_13/2, ⁶H_11/2, ⁶H_9/2 transitions of Dy³⁺, with the 575 nm (⁴F_9/2→⁶H_13/2) emission being the strongest under the excitation of 350 nm. The optimal Dy³⁺ concentration was determined to be 2 at%. Gd³⁺ co-doping apparently affect the phase and luminescence of the final product. The product undergoes a phase transformation from triclinic to monoclinic when Gd³⁺ doping level is over 25 at%. The emission intensity, quantum yield, color purity, and thermal stability of the (La_0.98Dy_0.02)₂W₂O₉ phosphor were comprehensively enhanced by Gd³⁺ co-doping and favorable quantum efficiency of 51.23% was obtained.     

Enhancement in electrical conductivity of Li<Subscript>2</Subscript>O: B<Subscript>2</Subscript>O<Subscript>3</Subscript>: V<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

The study of electrical conductivity of 30Li₂O: (70 − x) B₂O₃: xV₂O₅ glass samples has been carried out. The results have been explained by dividing the temperature range into two regions. In region I, conductivity shows Arrhenius behaviour for all the samples. The conductivity increases with addition of V₂O₅. The results have been explained in the light of Anderson and Stuart Model. In region II, an anomalous enhancement in the conductivity is observed for all the samples up to certain temperature beyond which the conductivity decreases. The enhancement in the conductivity in the annealed glass sample has been attributed to nanocrystallization.     

Dependence of photoluminescence (PL) emission intensity on Eu and ZnO concentrations in Y2O3:Eu and ZnO·Y2O3:Eu nanophosphors

Y₂O₃:Eu³⁺ and ZnO·Y₂O₃:Eu³⁺ nanophosphor powders with different concentrations of Eu³⁺ ions were synthesized by a sol-gel method and their luminescence properties were investigated. The red photoluminescence (PL) from Eu³⁺ ions with the main emission peak at 612 nm was observed to increase with Eu³⁺ concentration from 0.25 to 0.75 mol% and decreased notably when the concentration was increased to 1 mol%. The decrease in the PL intensity at higher Eu³⁺ concentrations can be associated with concentration quenching effects. The red emission at 612 nm was shown to increase considerable when ZnO nanoparticles were incorporated in Y₂O₃:Eu³⁺ while green emission from ZnO was suppressed. The increase is attributed to energy transfer from ZnO to Eu³⁺.     

Microwave dielectric properties of novel lithium containing pyrochlore type oxides: Li3Sm3 − xBixTi7Nb2O25 (x = 0, 1, 2 or 3)

Microwave dielectric properties of novel lithium ion containing pyrochlore type oxides: Li₃Sm_3 − xBi_xTi₇Nb₂O₂₅ (x = 0, 1, 2 or 3) have been reported in this paper. Powder X-ray diffraction patterns show that these oxides have cubic pyrochlore type structure. Ceramic microstructure of the sintered samples show well formed grains. They have relatively high dielectric constant (ε_r) in the range 80–137 at 1 MHz and ε_r, 45–83 at the resonant microwave frequency region. It is seen that the dielectric constant (ε_r) increases with the increase of Bi content. The best microwave dielectric properties obtained for fully substituted samarium compound, Li₃Sm₃Ti₇Nb₂O₂₅ are as follows: Q × f = 2007 and ε_r = 45 at the resonant microwave frequency, 3.78 GHz.     

Spectroscopic evaluation of Zn(PO3)2:Dy3+ glass as an active medium for solid state yellow laser

A spectroscopic investigation of zinc phosphate glass activated with 1.0, 5.0 and 10.0 mol% of Dy(PO₃)₃ is performed through absorption and luminescence spectra and decay times to study its potentialities for yellow laser operation upon excitation at 399 nm, which fits to the requirements of GaN LEDs. In the 1.0 mol% Dy(PO₃)₃-doped glass a quantum efficiency of 80 ± 5% was estimated for the dysprosium ⁴F_9/2 level luminescence, the ⁴F_9/2 → ⁶H_13/2 yellow emission shows greater intensity than the ⁴F_9/2 → ⁶H_15/2 blue emission, as well as a very high optical gain, which might make this glass phosphor a promising gain medium for solid state yellow laser pumped by GaN LEDs.     

Photoluminescence properties of novel KBaBP2O8:M (M = Pb2+ and Bi3+) phosphors

A series of novel inorganic phosphors KBa_1−xPb_xBP₂O₈ and K_1+xBa_1−2xBi_xBP₂O₈ (0.01 ⩽ x ⩽ 0.08) were synthesized by using a solid-state reaction technique at high-temperature and their photoluminescence properties were investigated. The dependence of the emission intensity on the Pb²⁺ and Bi³⁺ concentration for the KBa_1−xPb_xBP₂O₈ and K_1+xBa_1−2xBi_xBP₂O₈ was studied, in which the optimal concentration as well as the critical transfer distance R_c for Pb²⁺ and Bi³⁺ was obtained and determined. The as-prepared phosphors can be effectively excited with ultraviolet (UV), and exhibit UV − blue emission with large Stokes shift. The above work indicates these phosphors could be potential candidates for application in UV lamps industry.     

Structural and optical properties of (100 − x)(Li2B4O7) − x(SrO–Bi2O3–0.7Nb2O5–0.3V2O5) glasses and glass nanocrystal composites

Glasses of various compositions in the system (100 − x)(Li₂B₄O₇) − x(SrO–Bi₂O₃–0.7Nb₂O₅–0.3V₂O₅) (10  x  60, in molar ratio) were prepared by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Glass composites comprising strontium bismuth niobate doped with vanadium (SrBi₂(Nb_0.7V_0.3)₂O_9−δ (SBVN)) nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat-treated at 783 K/6 h) confirm the presence of rod shaped crystallites of SBVN embedded in Li₂B₄O₇ glass matrix. The optical transmission spectra of these glasses and glass nanocrystal composites of various compositions were recorded in the wavelength range 190–900 nm. Various optical parameters such as optical band gap (E_opt), Urbach energy (ΔE), refractive index (n), optical dielectric constant and ratio of carrier concentration to the effective mass (N/m^*) were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied.     

Spectroscopic and transport studies of Cu2+ ion doped in (40 —x)Li2O—xLiF—60Bi2O3 glasses

The preparation of (40-x)Li₂O-xLiF-60Bi₂O₃ glassy system and spectroscopic and transport studies of this system are reported. IR results show that this glass consists of [BiO₃] units and indicate formation of Bi-F bonds with the addition of LiF. From the ESR spectra of Cu²⁺ ion, the effectiveg values are found to vary slightly with increasing concentration of fluorine ion. The optical absorption peak corresponding to Cu²⁺ increased linearly with increasing concentration of LiF between 620 nm and 728 nm except at 2.5 mole% of LiF where its value is 729 nm. This peculiar behaviour is attributed to the varying structural coordination of fluorine as the concentration of lithium fluoride is increased. The ionic conductivity measurements indicate that the conduction is due to adiabatic hopping of polarons and the activation energies are found to be temperature and concentration dependent     

Upconversion nanotubes with tunable fluorescence properties based on Gd2 O2 S:Ln3+ (Ln3+ = Yb3+, Er3+) and derivatives for photodynamic therapy

In this study, Gd₂ O₂ S:Ln³⁺ (Ln³⁺  = Yb³⁺, Er³⁺) upconversion nanotubes (UCNTs) were synthesised by using Gd(OH)₃ :Ln³⁺ (Ln³⁺  = Yb³⁺, Er³⁺) nanotubes as the template. The luminescent and biological properties of Gd₂ O₂ S:Ln³⁺ (Ln³⁺  = Yb³⁺, Er³⁺) UCNTs, along with photodynamic therapy (PDT) applications of the Gd₂ O₂ S:8%Yb³⁺, 2%Er³⁺ UCNT–Ce6 (chlorin e6) nanocomposites, were systematically studied. The resultant UCNTs showed excellent biocompatibility with human retinal pigment cells (ARPE‐19) even after a prolonged incubation time of 72 h, and could be used as luminescent probes. Microscopic imaging revealed that the UCNTs existed mainly in cytoplasm. PDT studies on the Gd₂ O₂ S:8%Yb³⁺, 2%Er³⁺ UCNT–Ce6 nanocomposites indicate that the growth of the tumour (cell) could be inhibited dramatically when it was injected (incubated) with Gd₂ O₂ S:8%Yb³⁺, 2%Er³⁺ UCNT–Ce6 nanocomposites under the irradiation of 980 nm laser.Inspec keywords: biomedical materials, nanofabrication, tumours, cellular biophysics, nanomedicine, eye, biomedical optical imaging, nanocomposites, gadolinium compounds, ytterbium, photodynamic therapy, fluorescence, erbium, laser beam effectsOther keywords: luminescent properties, biological properties, photodynamic therapy applications, UCNT–Ce6 nanocomposites, upconversion nanotubes, tunable fluorescence properties, biocompatibility, human retinal pigment cells, microscopic imaging, PDT studies, tumour, laser irradiation, wavelength 980.0 nm, time 72.0 hour, Gd₂ O₂ S:Yb,Er     

Luminescent characteristics of LiSrBO3:M (M = Eu, Sm, Tb, Ce, Dy) phosphor for white light-emitting diode

LiSrBO₃:M (M = Eu³⁺, Sm³⁺, Tb³⁺, Ce³⁺, Dy³⁺) phosphors which have been developed for white light-emitting diodes (LEDs) were synthesized by a normal solid-state reaction. The emission and excitation spectra indicate that these phosphors can be effectively excited by near-ultraviolet light-emitting diodes (UVLED), and exhibit satisfactory red, green and blue performances, respectively, nicely fitting in with the widely applied UV chip. Under the condition of doping charge compensation Li⁺, Na⁺ and K⁺, the luminescence intensities of these phosphors were increased.     

The influence of auxiliary codopants on persistent phosphor Sr2P2O7:Eu2+,R3+ (R = Y,La, Ce,Gd, Tb and Lu)

We investigate the persistent luminescence in europium-doped strontium pyrophosphate upon codoping with auxiliary rare earth ions. The persistent phosphors are synthesized via solid-state reaction method under flowing N₂ + H₂. Under UV irradiation, broadband emission persistent luminescence located at 420 nm is observed in all of these phosphors at room temperature. The effects of auxiliary rare earth ions on Sr₂P₂O₇:Eu²⁺ are discussed according to the decay curves and thermoluminescence spectra. Sr₂P₂O₇:Eu²⁺,Lu³⁺ shows the best performance, while and La³⁺ and Ce³⁺ codoped samples are the weakest. The influence of auxiliary codopants is discussed in terms of ionic potential and ionic radius. We derive an empirical formula based on the experimental results.