Synthesis and photoluminescence properties of NaPbB5O9:Dy phosphor materials for white light applications

Given the recent increased interest in phosphor materials and their applications, we analyzed a new NaPbB₅O₉:Dy³⁺ phosphor material with different concentrations of Dy³⁺. In particular, we investigated the crystal structure, morphology, and luminescence properties of these materials. X-ray diffraction analyses confirmed the formation of NaPbB₅O₉:Dy³⁺ phosphor powder. The functional groups present in the phosphor materials were examined by Fourier transform infrared spectroscopy. Scanning electron microscope images showed that the size of the grains was in the micrometer range. Photoluminescence spectra were recorded at different excitation wavelengths for the phosphor materials and we analyzed the variation in the intensity of the emission bands with different concentrations of Dy³⁺ ions. The color co-ordinates were calculated and used to characterize the color of the phosphor. We found that the emission colors of the Dy³⁺-doped NaPbB₅O₉ powders depended on the Dy³⁺ ion doping concentration and the excitation wavelength.     

Effect of Yb3+ concentration on photoluminescence properties of cubic Gd2O3 phosphor

Yb³⁺ doped phosphor of Gd₂O₃ (Gd₂O₃:Yb³⁺) have been prepared by solid state reaction method. The structure and the particle size have been determined by X-ray powder diffraction measurements. The average particle size of the phosphor is in between 35 and 50 nm. The particle size and structure of the phosphor was further confirmed by TEM analysis. The visible and NIR luminescence spectra were recorded under the 980 nm laser excitation. The visible upconversion luminescence of Yb³⁺ ion was due to cooperative luminescence and the presence of rare earth impurity ions. The cooperative upconversion and NIR luminescence spectra as a function of Yb³⁺ ion concentration were measured and the emission intensity variation with Yb³⁺ ion concentration was discussed. Yb³⁺ energy migration quenched the cooperative luminescence of Gd₂O₃:Yb³⁺ phosphor with doping level over 5%, while the NIR emission luminescence continuously increases with increasing Yb³⁺ ion concentration.     

A novel Dy3+-doped Gd(PO3)3 white-light phosphors under VUV excitation for Hg-free lamps application

Novel Dy³⁺-doped Gd(PO₃)₃ white light phosphors each with an orthorhombic system are successfully synthesized by solid-state reaction. The luminescence properties of white-light Gd_1-x(PO₃)₃:xDy³⁺ (0<x≤ 0.25) under vacuum ultraviolet (VUV) excitation are investigated. The strong absorption at around 147 nm in excitation spectrum energy can be transferred to the energy levels of Dy³⁺ ion from the host absorption. Additionally, the white light phosphor is activated by a single Dy³⁺ ion. Therefore, the luminescence of Gd_1-x(PO₃)₃:xDy (0<x≤ 0.25) under VUV excitation is effective, and it has the promise of being applied to mercury-free lamp.     

Luminescence and energy transfer in phosphor LiAl5O8: Ce3+, Dy3+

Ce³⁺ and Dy³⁺-doped LiAl₅O₈ were synthesized in the present study. The luminescence properties of Ce³⁺ and Dy³⁺, and the energy transfer from Ce³⁺ to Dy³⁺ were investigated. The Ce³⁺ species in LiAl₅O₈ emit one broad band that peaks at 351 nm under the excitation of ultraviolet light, which is attributed to the 5d–4f transitions of Ce³⁺. The luminescence of Dy³⁺ in singly doped LiAl₅O₈ can not be detected due to its low oscillator strength. However, Dy³⁺ emit intense blue (477 nm) and yellow (569 nm) light after the introduction of Ce³⁺. This phenomenon demonstrates that there exists effective energy transfer from Ce³⁺ to Dy³⁺, which occurs because the emission spectrum of Ce³⁺ perfectly overlays the excitation spectrum of Dy³⁺. The energy transfer from Ce³⁺ to Dy³⁺ is performed through dipole–dipole interactions. The experimental results show that LiAl₅O₈ co-doped with Ce³⁺ and Dy³⁺ can be a potential two-band (blue and yellow) phosphor.     

Photoluminescence of Rare Earth Phosphors Na0.5Gd0.5WO4: RE3+ and Na0.5Gd0.5(Mo0.75W0.25)O4: RE3+ (RE=Eu, Sm, Dy)

Two series of phosphors, Na_0.5Gd_0.5WO₄: RE³⁺ and Na_0.5Gd_0.5(Mo_0.75W_0.25)O₄: RE³⁺ (RE?=?Eu, Sm, Dy) have been synthesized by hydrothermal process to obtain the high purity, which have been characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM). The results suggest that Na_0.5Gd_0.5(Mo_0.75W_0.25)O₄: RE³⁺ phosphors are more easily to crystallize than Na_0.5Gd_0.5WO₄: RE³⁺ ones. Both of them present the characteristic luminescence of Eu³⁺, Sm³⁺ and Dy³⁺. Especially the photoluminescent properties of Na_0.5Gd_0.5WO₄: x%Eu³⁺ (Sm³⁺) can be obtained to show white luminescence as the suitable doping concentration of Eu³⁺ or Sm³⁺.     

Emission analysis of Li6LuY(BO3)3:Tb3+,Dy3+ phosphors

In this paper, we present the synthesis and luminescence properties of Tb³⁺ and Dy³⁺-doped lithium lutetium yttrium borate (Li₆LuY(BO₃)₃) phosphors. We have adopted the well-known solid state reaction method for the synthesis of these phosphors. The emission intensities of the synthesized phosphors were found to reach their maximum, when doped by 1 mol% of Tb³⁺ and 3 mol% of Dy³⁺, beyond which emission intensities decrease due to concentration quenching. The homogeneous phase, crystalline structure and uniform morphology of the synthesized phosphors were confirmed by X-ray diffraction analysis (XRD) and Scanning electron microscopy (SEM). The X-ray and UV–VIS-induced luminescence, decay time and CIE chromaticity were investigated for the synthesized phosphors.The X-ray induced integrated light yield was measured to be 82% for Li₆LuY(BO₃)₃:Tb³⁺ (LLYBO) and 59% for Li₆LuY(BO₃)₃:Dy³⁺ of that of commercially available X-ray imaging material; Gd₂O₂S:Tb³⁺ (Gadox).LLYBO:Tb³⁺ phosphor displayed five major emission bands that correspond to ⁵D_j → ⁷F_j transitions. The 1931 Commission Internationale de l'Eclairage (CIE) chromaticity coordinates were also measured.     

Enhanced photoluminescence of Sm/Bi co-doped Gd2O3 phosphors by combustion synthesis

Gd₂O₃:Sm³⁺ and Gd₂O₃:Sm³⁺,Bi³⁺ powders were prepared by a combustion method. Their structures were determined using X-ray diffraction. UV-visible absorption and photoluminescence spectra were investigated for Gd₂O₃:Sm³⁺ and Gd₂O₃:Sm³⁺,Bi³⁺ at different annealing temperatures and different doping concentrations. The emission spectra of all samples presented the characteristic emission narrow lines arising from the ⁴G_5/2→⁶H_J transitions (J=5/2, 7/2, and 9/2) of Sm³⁺ ions upon excitation with UV irradiation. The emission intensity of Sm³⁺ ions was largely enhanced with introducing Bi³⁺ ions into Gd₂O₃:Sm³⁺ and the maximum occurred at a Bi³⁺ concentration of 0.5 mol%. The relevant mechanisms were discussed with the sensitization theory by Dexter and the aggregation behavior of Bi³⁺ ions.     

Optical properties of crystals doped with Sm3+ or Dy3+ relevant to potential InGaN/GaN laser diode-pumped visible laser operation: A comparative study

Results of detailed spectroscopic investigation of Sm³⁺ and Dy³⁺ ions incorporated in crystal structures of Yal YAl₃(BO₃)₄, LiNbO₃, Gd₃Ga₅O₁₂, Gd₂SiO₅, Lu₂SiO₅ and (Gd, Lu)₂SiO₅ are reported and discussed. The impact of the hosts on transition intensities and excited state relaxation dynamics of incorporated luminescent ions was examined. Distribution of luminescence intensity among spectral bands in terms of luminescence branching ratios was evaluated based on numerical integration of luminescence bands. Intensities of UV and blue absorption bands potentially useful for optical pumping were determined quantitatively in units of absorption cross section. The most intense luminescence bands related to potential laser transitions ⁴ G _5/2 → ⁶ H _7/2 of Sm³⁺ around 600 nm and ⁴ F _9/2 → ⁶ H _13/2 of Dy³⁺ around 580 nm were calibrated in units of emission cross section. Evaluated peak values of emission cross section range from 0.43 × 10^?20 cm² for Sm³⁺ in (Gd, Lu)₂SiO₅ to 1.17 × 10^?20 cm² for Sm³⁺ in LiNbO₃. Those for dysprosium-doped crystals range from 0.63 × 10^?20 cm² for LiNbO₃:Dy³⁺ to 2.0 × 10^?20 cm² for Yal YAl₃(BO₃)₄:Dy³⁺. It follows from these considerations that samarium-doped crystals show promise for laser application owing to the combination of a strong absorption that matches radiation of commercial laser diodes emitting near 405 nm and long luminescence lifetime. Major shortcoming of dysprosium-doped crystals results from a weak intensity of absorption bands available for optical pumping near 450 nm and 385 nm combined with relatively strong self-quenching of luminescence.     

Luminescence property improvement of Ba2LaSbO6:Mn4+ phosphor by using Dy3+ or H3BO3

Ba₂LaSbO₆:Mn⁴⁺, Ba₂LaSbO₆:Mn⁴⁺, Dy³⁺, and Ba₂LaSbO₆:Mn⁴⁺, H₃BO₃ phosphors are synthesized in the air by high temperature solid state reaction method. The particle sizes and sintering degree of Ba₂LaSbO₆:Mn⁴⁺ phosphor may be changed by doping Dy³⁺ ion and H₃BO₃. When the small amount of Dy³⁺ ion and H₃BO₃ are codoped, the emission intensity of Ba₂LaSbO₆:Mn⁴⁺ phosphor can be enhanced 1.2–1.3 times and the quantum efficiency of Ba₂LaSbO₆:Mn⁴⁺ phosphor can be improved. The lifetime of Ba₂LaSbO₆:Mn⁴⁺ phosphor may be changed by doping Dy³⁺ ion and H₃BO₃. The experimental results are valuable in research of luminescence property of Mn⁴⁺-doped luminescence materials.     

The luminescence properties of Dy3+-activated SrB4O7 under VUV excitation

Dy³⁺-doped SrB₄O₇ phosphors were synthesized by solid-state reaction. The luminescence properties of white-light SrB₄O₇:Dy³⁺ under vacuum ultraviolet (VUV) excitation were firstly investigated. According to strong absorption around 147 nm in excitation spectra, energy can easily be transferred to the energy levels of Dy³⁺ from host absorption, and hence luminescence of SrB₄O₇:Dy³⁺ under VUV excitation was effective, and it has the potential of being applied to a white lamp-house for mercury-free lamp.     

Crystalline-phase-dependent red emission behaviors of Gd2O3:Eu3+ thin-film phosphors

Gd₂O₃:Eu³⁺ luminescent thin films have been grown on Al₂O₃(0001) substrates using pulsed-laser deposition. The films grown at different deposition conditions showed different crystalline phases, surface morphologies and luminescent characteristics. Both cubic and monoclinic crystalline phases were observed for the Gd₂O₃:Eu³⁺ films, and the crystalline structure and the surface morphology of the films were highly dependent on the oxygen pressure and substrate temperature. The cubic system showed a higher luminescence than the monoclinic system. The luminescence characteristics were strongly influenced by not only the crystalline structure but also the surface morphology of the films. The photoluminescencebrightness data obtained from Gd₂O₃:Eu³⁺ films indicate that Al₂O₃(0001) is a promising substrate for growth of high-quality Gd₂O₃:Eu³⁺ thin-film red phosphor. In particular, the Gd₂O₃:Eu³⁺ films showed a much better photoluminescence behavior than a Y₂O₃:Eu³⁺ films with the same thickness. PACS 78.20.-e; 78.55.-m; 78.66.-w     

A novel Dy3+-doped GdPO4 white-light phosphors under vacuum ultraviolet excitation for Hg-free lamps application

Novel Dy3+-doped GdPO4 white light phosphors with monoclinic system were successfully synthesised by hydrothermal method at 240 ℃. This paper investigates the luminescence properties of white-light Gd1-xPO4 : xDy3+ under vacuum ultraviolet (VUV) excitation. The strong absorption at around 147 nm in excitation spectrum energy can be transferred to the energy levels of Dy3+ ion from the host absorption. Additionally, this white light phosphors are activated by a single Dy3+ ion and with a lower preparation temperature, which tend to decrease the consumption of rare earth resource and energy. Therefore, the luminescence of Gd1-xPO4 : xDy3+ under VUV excitation is effective, and proves to be promising in application to mercury-free lamp.     

Elaboration of nanostructured Eu3+-doped Gd2O3 phosphor fine spherical powders using polyol-mediated synthesis

Red-emitting Eu³⁺-doped Gd₂O₃ spherical powders were directly precipitated using a polyol method. The as-synthesized powders consist of agglomerates with a spherical shape and a size ranging between 0.4 and 0.6 μm. Each agglomerate is nanostructured and consists of a packing of nanocrystallites (3–5 nm) of a bcc oxide phase whose luminescence presents original features in comparison with bulk materials. The powders were further calcinated and the size of both crystallites and agglomerates, the crystalline structure and the luminescence were studied as a function of the annealing temperature. For temperatures lower than 900 °C, the samples obtained are highly crystalline and possess the classical Eu³⁺ red luminescence. For optimized temperature, the morphology of the particles can be preserved leading to spherical, dense, luminescent and almost monodisperse oxide powders, 0.5 μm in size. PACS 81.07.Bc; 81.07.Wx; 81.16.Be; 75.50.-y; 42.70.-a     

Analysis of Energy Transfer and Concentration Quenching in Sm3+-Activated Borate GdB3O6 Phosphors by Means of Fluorescence Dynamics

This article reports on the optical properties of Sm³⁺-activated GdB₃O₆ phosphors based on the measurement of their photoluminescence spectra and luminescence decay curves. Energy transfer from Gd³⁺ to Sm³⁺ and the concentration quenching of the Sm³⁺ ion emission are investigated. From the photoluminescence spectra and decay curves, the energy transfer from Gd³⁺ to Sm³⁺ is confirmed. The concentration quenching of the Sm³⁺ ion emission can be ascribed to resonant cross-relaxation. The interaction between the Sm³⁺ ions is derived of the electric dipole–dipole type through fitting the data with the Inokuti-Hirayama model. The critical distances and energy transfer microparameter for the transfer processes are given. The decay curves of Sm³⁺⁴G_5/2 level exhibiting a buildup and decay process also confirm the energy transfer from Gd³⁺ to Sm³⁺ and between Sm³⁺ ions.     

Influence of Gd3+ and Dy3+ co-doping and sintering regime on enhancement of electrical conductivity of ceria-based solid electrolyte

In order to improve the conductivity of ceria-based solid electrolytes, effect of co-doped Gd³⁺ and Dy³⁺ was evaluated. For this purpose, nano-crystalline Gd_0.2???x Dy _x Ce_0.8O_1.9 powders with various composition ranges (x?=?0.05, 0.1, 0.15, 0.2) were initially synthesized by high-energy milling method. The effect of micro-structural evolution and co-doping on electrical properties of the dense sintered samples fabricated by two-step sintering and conventional sintering of the synthesized powders were investigated. Electrical conductivity of the samples was discussed based on the results obtained by AC impedance spectroscopy at temperatures in the range of 300–700 °C. The co-doping and sintering regime were found to significantly influence the conductivity of the electrolytes. The electrical conductivity of the co-doped samples depends on Dy³⁺ content and the maximum conductivity obtained by 0.15 mol% Dy and 0.05 mol% Gd. The conductivity of Gd_0.2???x Dy _x Ce_0.8O_1.9 (x?=?0.15) was 0.03 S/cm at 700 °C. A thorough discussion was made, based on the present experimental data.     

Synthesis and photoluminescence properties of Sm-doped LaMgB5O10 and GdMgB5O10

Luminescence and reflection spectra as well as luminescence kinetics of the 1 mol% Sm³⁺-doped crystalline lanthanum magnesium meta borate (LaMgB₅O₁₀) and gadolinium magnesium meta borate (GdMgB₅O₁₀) were analyzed. Materials were synthesized by conventional solid state route and showed bright orange-red emission under UV excitation. Emission spectra contain sharp and well resolved Sm³⁺⁴G_5/2→⁶H_J transitions indicating a strong crystal-field effect. In case of gadolinium compound energy transfer between Gd³⁺ and Sm³⁺ was detected. The luminescent kinetics of the Sm³⁺ in analyzed powders is characterized by single exponential decay and experimental values vary in the range 2.2-2.4 ms.     

Photoluminescence properties of Eu3+-doped Gd2MoB2O9 phosphors for LED-based solid-state-lighting

Investigation was performed on luminescent properties of novel Gd_2−x Eu _x MoB₂O₉ (0.02≤x≤2.0) phosphors. The excitation spectra consist of broad band and intense narrow lines. The 4f-4f transitions are situated in a favorable position for excitation by GaN chip emission. The emission spectra consist of transitions from the ⁵D₀ level to the lower ⁷F manifold, and the emission shows no concentration quenching at higher doping level. The decay time spectra of the ⁵D₀ → ⁷F₂ emission are recorded. Under 395 nm excitation, the intensity of ⁵D₀ → ⁷F₂ transition of GdEuMoB₂O₉ is 1.2 times stronger than that of commercial Eu³⁺:Y₂O₂S phosphor. Gd₂MoB₂O₉:Eu³⁺ phosphors are promising candidates for near-UV-based solid-state-lighting (SSL).     

The effect of charge compensation by means of Na+ ions on the luminescence behavior of Sm3+-doped CaAl4O7 phosphor

Results of structural and spectroscopic measurements of Sm³⁺ doped calcium aluminates: Ca_1?xSm_xAl₄O₇ and Ca_1?2xSm_xNa_xAl₄O₇ (x=0.0005, 0.002, 0.01, 0.02, 0.03, 0.05) obtained by the modified Pechini method are presented. All samples yield intense orange–red emission under violet excitation (404.5 nm). Narrow bands corresponding to characteristic f–f intraconfigurational transition of Sm³⁺ in excitation and emission spectra were observed. The influences of the concentration of Sm³⁺ as well as charge compensation by co-doping with Na⁺ ions on the luminescent properties of the phosphor were investigated. Detailed analysis of the emission spectra of Sm³⁺ doped and Sm³⁺,Na⁺ co-doped CaAl₄O₇ powders proved that activator ions substitute Ca²⁺ in the host. Co-doping with Na⁺ ions enhanced greatly the intensity of the luminescence. Concentration dependencies of the intensity of luminescence and its decay kinetics proved the emission quenching at higher dopant contents due to cross-relaxation processes between Sm³⁺ ions. Fitting of the ⁴G_5/2 state fluorescence decay to the Inokuti–Hirayama model indicated dipole–dipole interaction as the dominant mechanism of the cross-relaxation processes.     

The dependence of luminescence on reduction of Sm2+ ions doped in lithium barium borate glasses

Sm³⁺-doped Li₂O–BaO–B₂O₃ glass was prepared by the conventional melt quenching method in air atmosphere. Sm²⁺ ions were obtained by two methods, i.e. heating the as-made glass in a reducing atmosphere and irradiating the sample under X-rays. The two obtained samples were investigated by luminescence spectra and lifetime measurements. It was found that the conversion of Sm³⁺→Sm²⁺ after X-ray irradiation is efficient in this borate glass. Photo-stability of Sm²⁺ ions was evaluated by the photo-bleaching method. Furthermore, thermo-luminescence was also measured. The different defects and the reduction mechanism of Sm²⁺ ions in this borate glass were discussed. This would be helpful to understand the reduction mechanism of Sm²⁺ ions in borate glasses.     

SrAl_2B_2O_7:Dy~(3+)材料的制备及其发光性能

采用高温固相法制备了SrAl2B2O7:Dy3+发光材料.在350nm紫外光激发下,测得SrAl2B2O7:Dy3+材料的发射光谱为一个多峰宽谱,主峰分别为480,573和678nm;分别和Dy3+的4F9/2→6H15/2,4F9/2→6H13/2,4F9/2→6H11/2的跃迁发射相对应;监测573nm的发射峰,得到材料的激发光谱为一个多峰宽谱,主峰分别为295,325,350,365,400nm.研究了Dy3+掺杂浓度对SrAl2B2O7:Dy3+材料发射光谱的影响,随着Dy3+掺杂浓度的增大,SrAl2B2O7:Dy3+材料的Iy/Ib逐渐增大,根据Judd-Ofelt理论解释了其原因.随着Dy3+掺杂浓度的增大,Dy3+的4F9/2→6H13/2跃迁产生的573nm发射峰强度先增大,在4%时达到最大值,之后减小,其自身的浓度猝灭机理为电偶极-电偶极相互作用.不同的电荷补偿剂Li+,Na+,K+的引入均使发光强度得到提高,尤其以Li+最佳,发光强度提高了大约33%.