Synthesis and luminescence characterization of Pr3+, Gd3+ co-doped SrF2 transparent ceramics

Pr³⁺, Gd³⁺ co-doped SrF₂ transparent ceramic, as the potential material for visible luminescent applications, was prepared by hot-pressing of precursor nanopowders. The microstructure, phase compositions, and in-line transmittance, as well as the photoluminescence properties were investigated systematically. Highly optical quality Pr,Gd:SrF₂ transparent ceramic with nearly pore-free microstructure was obtained at 800°C for 1.5 hours. The average in-line transmittance of the x at.% Pr, 6 at.% Gd:SrF₂ (x = 0.2, 0.5, 1.0, 2.0) transparent ceramics reached to 87.3 % in the infrared region. The photoluminescence spectra presented intense visible light emissions under the excitation of 444 nm, the main intrinsic emission bands located at 483 and 605 nm, which were attributed to the transitions of Pr³⁺: ³P₀ → ³H₄ and ¹D₂ → ³H₄, respectively. With the co-doping of Gd³⁺ ions, the emission intensity of the Pr:SrF₂ transparent ceramic was greatly enhanced. All the emission bands of x at.% Pr, 6 at.% Gd:SrF₂ transparent ceramics exhibited the highest luminescence intensity with the 1.0 at.% Pr³⁺ doping concentrations, whereas the lifetimes decreased dramatically with the Pr³⁺ doping contents increasing from 0.2 to 2.0 at.% due to its intense concentration quenching effect. The 1 at.% Pr, 6 at.% Gd:SrF₂ transparent ceramic is a promising material for visible luminescent device applications.     

Photoluminescence properties of Pr3+ ion-doped YInGe2O7 phosphor under an ultraviolet irradiation

Pr³⁺ ion-doped YinGe₂O₇ phosphors are synthesized by a vibrating milled solid state reaction. There is a red shift for the excitation peak for the charge transfer transition between In³⁺ and O^2- ion because the numbers of oxygen vacancies change the structure, which leads to a change in the crystal field. The results indicate that the emission spectra for the YinGe₂O₇:Pr samples under an excitation of 263 nm exhibit two dominant peaks at 486 and 604 nm, which are respectively assigned to the ³P₀→³H₄ and ¹D₂→³H₄ transitions. The chromaticity coordinate for (Y_1?xPr_x)InGe₂O₇ phosphors varies with the Pr³⁺ doping concentration, from white, to greenish, to blueish. This has a potential application as a white light emitting phosphor for ultraviolet light-emitting diodes.     

Energy transfer and controllable colors of upconversion emission in Er3+ and Dy3+ co-doped CaF2 transparent ceramics

x at. % Er³⁺, 3 at. % Dy³⁺: CaF₂ transparent ceramics (x=1-5) with good transparency were fabricated by hot-pressed sintering. The phase composition of nanoparticles and transparent ceramics, microstructure, in-line transmittance, upconversion spectra and lifetime of transparent ceramics, as well as energy transfer mechanism between Er³⁺ and Dy³⁺ were investigated. The mean grain sizes of nanoparticles decreased from 33.0 nm to 26.2 nm with the Er³⁺ doping concentration increasing from 1 to 5 at.%. The microstructure of ceramic samples presented nearly dense microstructure and EDS analysis indicated Er³⁺ and Dy³⁺ were uniformly incorporated into CaF₂ lattice. Under 900 nm excitation, the emission intensity for ⁴F_9/2→⁶H_15/2 transition of Dy³⁺ decreased and for ⁴S_3/2→⁴I_15/2 transition of Er³⁺ increased, the lifetime for the ⁴F_9/2 level of Dy³⁺ decreased while the ⁴F_7/2 level of Er³⁺ increased with the raise of Er³⁺ doping concentration. The energy transfer mechanism was proved to be the dipole-dipole interaction. The upconversion luminescence color was tuned from orange through yellow to green by changing the Er³⁺/Dy³⁺ ratio. In addition, the Vickers hardness, fracture toughness, and the thermal conductivity of Er³⁺, Dy³⁺: CaF₂ transparent ceramics were discussed. All the results showed the Dy³⁺ could be used as a sensitizer for Er³⁺: CaF₂ transparent ceramic in the upconversion field.     

Fabrication and properties of transparent Tb:YAG fluorescent ceramics with different doping concentrations

Terbium doped yttrium aluminum garnet (Tb:YAG) transparent ceramics with different doping concentrations were fabricated by the solid-state reaction method using commercial Y₂O₃, α-Al₂O₃ and Tb₄O₇ powders as raw materials. Samples sintered at 1750 °C for 20 h were utilized to observe the optical transmittance, microstructure and fluorescence characteristics. It is found that all the Tb: YAG ceramics with different doping concentrations exhibit homogeneous structures with grain size distributions around 22–29 µm. For the 5 at% Tb:YAG transparent ceramics, the grain boundaries are clean with no secondary phases. The photoluminescence spectra show that Tb:YAG ceramics emit predominantly at 544 nm originated from the energy levels transition of ⁵D₄→⁷F₅ of Tb³⁺ ions, and the intensity of the emission peak reaches a maximum value when the Tb³⁺ concentration is 5 at%. The in-line transmittance of the 5 at% Tb:YAG ceramics is 73.4% at the wavelength of 544 nm, which needs to be further enhanced by optimizing the fabrication process. We think that Tb:YAG transparent ceramics may have potential applications in the high-power white LEDs.     

Gd3+ doping induced microstructural evolution and enhanced visible luminescence of Pr3+ activated calcium fluoride transparent ceramics

Transparent Pr³⁺ doped Ca_1-xGd_xF_2+x (x = 0, 0.01, 0.03, 0.06, 0.10, 0.15) polycrystalline ceramics with fine-grained microstructures were prepared by the hot-pressing method. The dependence of microstructure, optical transmittance, luminescence performances and mechanical properties on the Gd³⁺ concentrations for Pr³⁺:Ca_1-xGd_xF_2+x transparent ceramics were investigated. The Gd³⁺ ions show positive effects on the microhardness of Pr³⁺:Ca_1-xGd_xF_2+x transparent ceramics as a result of the decrease in the grain sizes. Excited by the Xenon lamp of 444 nm, typical visible emissions located at 484 nm, 598 nm and 642 nm were observed. Furthermore, the incorporation of Gd³⁺ ions can greatly enhance the photoluminescence performance owing to the improvement in the concentration quenching effect. The quenching concentration of Pr³⁺ ions in CaF₂ transparent ceramics increased to 1 at.% as a result of the positive effect of Gd³⁺ codoping. The energy transfer mechanism of Pr³⁺ in the Pr³⁺:Ca_1-xGd_xF_2+x transparent ceramics has been investigated and discussed.     

Effect of NaF doping on the transparency,microstructure and spectral properties of Yb3+: CaF2 transparent ceramics

Yb³⁺:CaF₂ transparent ceramics are promising laser gain media with outstanding performance. However, low transmittance in the visible range is the main challenge that restricts the application of Yb³⁺:CaF₂ ceramics in the laser system. In this paper, a new scheme to eliminate the residual pores in the Yb³⁺:CaF₂ transparent ceramics based on doping of NaF as a sintering aid is proposed. Microstructural characterization indicated that NaF could inhibit the grain growth and increase the transmittance in the visible range significantly. The corresponding transmittance was measured to be 85% at the wavelength of 400 nm. The spectra results showed that co-doped with Na⁺ ions could break the clusters of Yb³⁺ ions and modulate the spectroscopy properties of Yb³⁺: CaF₂ lattice efficiently. This paper proved that doping with NaF is an efficient strategy to improve the transmittance and fluorescence quantum efficiency of Yb³⁺:CaF₂ transparent ceramics.     

Fabrication and upconversion luminescence properties of Er:SrF2 transparent ceramics compared with Er:CaF2

SrF₂ transparent ceramic is a promising upconversion material due to the low phonon energy. The effect of different sintering temperatures on Er:SrF₂ transparent ceramics was investigated. The suitable sintering temperature for Er:SrF₂ transparent ceramics was 900 °C by hot-pressed sintering in this study. High quality of Er:SrF₂ transparent ceramics with different doping concentrations were obtained. The upconversion luminescence spectra and decay behavior were compared between Er:SrF₂ and Er:CaF₂ transparent ceramics with different Er³⁺ doping concentration. The green emission of 5 at.% Er:SrF₂ ceramic was much stronger than that of 5 at.% Er:CaF₂ ceramic, while the red emission of Er:SrF₂ ceramic was almost the same as that of Er:CaF₂ ceramic. The upconversion luminescence lifetime of Er:SrF₂ transparent ceramics was longer than that of Er:CaF₂.All the results indicated Er:SrF₂ transparent ceramics was a candidate for green fluorescent upconversion materials.     

Structural,mechanical, thermal and optical properties of Yb,Pr-doped Y4Zr3O12 ceramics

In the present work, Y₄Zr₃O₁₂ bulk ceramics doped with Yb³⁺ and Pr³⁺ were characterized to assess their structural, mechanical, thermal and optical properties. Specimens were synthesized by the polymerizable complex method and sintered as pellets at 1550?°C for 2?h. Samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers-indentation method, thermodilatometry, laser flash method, diffuse reflectance and luminescence spectroscopies. All compositions exhibit cubic like-fluorite structure, low thermal conductivity, moderate fracture toughness and thermal expansion coefficient values comparable to those of other yttria-stabilized zirconias. Regarding the optical properties, diffuse reflectance spectra support the oxidation of praseodymium from Pr³⁺ to Pr⁴⁺ in the Pr-doped specimens. When irradiated under an IR laser (975?nm), only the pellet containing Yb³⁺ showed white light emission at low and room pressures, but not the undoped, and those pellets doped or codoped with Pr. These results demonstrate that it is possible to produce white light not only in nanostructured systems but also in bulk ceramic oxides, and that the introduction of additional electronic states within the band gap of the host associated with the Pr, inhibits the generation of the white light.     

Spectrum regulation of YAG:Ce transparent ceramics with Pr,Cr doping for white light emitting diodes application

YAG:Ce transparent ceramics with high luminous efficiency and color render index were prepared via a solid state reaction-vacuum sintering method. Cr³⁺and Pr³⁺ were applied to expand the spectrum of YAG:Ce transparent ceramics. As prepared ceramics exhibit luminescence spectrum ranging from 500 nm to 750 nm, which almost covers full range of visible light. After the concentration optimization of Ce³⁺, Pr³⁺ and Cr³⁺, high quality white light was obtained by coupling the YAG:Ce,Pr,Cr ceramics with commercial blue LED chips. Color coordinates of the YAG:Ce,Pr,Cr ceramics under 450 nm LED excitation vary from cold white light to warm white light region. The highest luminous efficiency of WLEDs encapsulated by transparent YAG:Ce,Pr,Cr ceramic was 89.3 lm/W, while its color render index can reach nearly 80. Energy transfers between Ce³⁺ → Pr³⁺ and Ce³⁺ → Cr³⁺ were proved in co-doped ceramic system. Transparent luminescence ceramics accomplished in this work can be quite prospective for high power WLEDs application.     

Color-tunable up-conversion luminescence of Zn(AlxGa1-x)2O4:Yb3+,Tm3+,Er3+ powders

Color-tunable up-conversion powder phosphors Zn(Al_xGa_1-x)₂O₄: Yb³⁺,Tm³⁺,Er³⁺ were synthesized via high temperature solid-state reaction. Also, the morphological and structural characterization, up-conversion luminescent properties were all investigated in this paper. In brief, under the excitation of a 980?nm laser, all powders have same emission peaks containing blue emission at 477?nm (attributed to ¹G₄→³H₆ transition of Tm³⁺ ions), green emission at 526?nm and 549?nm (attributed to ²H_11/2→ ⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transition of Er³⁺ ions respectively), red emission at about 659?nm and 694?nm (attributed to ⁴F_9/2→⁴I_15/2 transition of Er³⁺ ions and ³F₃→³H₆ transition of Tm³⁺ ions, respectively), which are not changed after the doping of Al³⁺ ions. However, the doping of Al³⁺ ions can enhance the up-conversion luminescent intensity and efficiency, while the emission color of as-prepared powder phosphors can be tunable by controlling the doping amount of Al³⁺ ions. Taking Zn(Al_0.5Ga_0.5)₂O₄:Yb,Tm,Er as the cut-off value, the emissions have clear blue-shift firstly and then show obvious red-shift with the increasing doping of Al³⁺ ions. Stated thus, pink emission in ZnAl₂O₄:Yb,Tm,Er, purplish pink emission in ZnGa₂O₄:Yb,Tm,Er and Zn(Al_0.9Ga_0.1)₂O₄:Yb,Tm,Er, purple emission in Zn(Al_0.1Ga_0.9)₂O₄:Yb,Tm,Er and Zn(Al_0.3Ga_0.7)₂O₄:Yb,Tm,Er, purplish blue emission in Zn(Al_0.7Ga_0.3)₂O₄:Yb,Tm,Er, blue emission in Zn(Al_0.5Ga_0.5)₂O₄:Yb,Tm,Er can be observed, which confirm the potential applications of as-prepared Zn(Al_xGa_1-x)₂O₄:Yb³⁺,Tm³⁺,Er³⁺ powder phosphors in luminous paint, infrared detection and so on.     

Structural,spectroscopic and thermal properties of hot-pressed Nd:(Ca0.94Gd0.06)F2.06 transparent ceramics

0.5–5.0?at.% Nd³⁺ doped (Ca_0.94Gd_0.06)F_2.06 transparent ceramics were fabricated by vacuum hot-pressing sintering. The structural, spectroscopic and thermal properties of Nd:(Ca_0.94Gd_0.06)F_2.06 transparent ceramics, as well as the influence of Nd³⁺ content on these properties were investigated. The as-fabricated ceramic samples exhibited high transparency and nearly pore-free microstructure. The absorption peaks located at 538?nm, 576?nm, 736?nm, 792?nm and 865?nm were attributed to the transitions from ground state to the excited states of Nd³⁺ ions, and the absorption coefficients increased linearly with Nd³⁺ content increasing. The emission band of the sample doped with 1?at.% Nd³⁺ concentration exhibited the highest emission intensity, while the lifetime decreased sharply with the increase of Nd³⁺ concentration. In addition, with Nd³⁺ content increasing from 0.5 to 5.0?at.%, the thermal expansivity coefficients increased slightly, while the thermal conductivity decreased from 4.21 to 2.36?W/m?K at room temperature.     

Fabrication,microstructure and spectroscopic properties of Yb:Lu2O3 transparent ceramics from co-precipitated nanopowders

Ytterbium doped lutetium oxide (Yb:Lu₂O₃) transparent ceramics were fabricated by vacuum sintering combined with hot isostatic pressing (HIP) of the powders synthesized by the co-precipitation method. The effects of calcination temperature on the composition and morphology of the powders were investigated. Fine and well dispersed 5?at% Yb:Lu₂O₃ powders with the mean particle size of 67?nm were obtained when calcined at 1100?°C for 4?h. Using the synthesized powders as starting material, we fabricated 5?at% Yb:Lu₂O₃ ceramics by pre-sintering at different temperatures combined with HIP post-treatment. The influence of pre-sintering temperature on the densities, microstructures and optical quality of the 5?at% Yb:Lu₂O₃ ceramics was studied. The ceramic sample pre-sintered at 1500?°C for 2?h with HIP post-treating at 1700?°C for 8?h has the highest in-line transmittance of 78.2% at 1100?nm and the average grain size of 2.6?µm. In addition, the absorption and emission cross sections of the 5?at% Yb:Lu₂O₃ ceramics were also calculated.     

Solid state reaction preparation and enhanced red luminescence of S-doped La2Mo2O9:Prphosphors

Red-light-emitting phosphors of La₂Mo₂O₉:Pr³⁺ and S-doped La₂Mo₂O₉:Pr³⁺ were prepared by high temperature solid state reaction. Under the excitation of 450 nm blue light, all samples produced a red emission peak at 650 nm corresponding to the characteristic transition of Pr³⁺ (³P₀→³F₂). The dependence of Pr³⁺ doping content (x) on the luminescent intensity was analyzed, and the optimal doping content of Pr³⁺ was x=0.07. After a small quantity of sulfur was introduced into the system, the luminescence intensity of phosphors was obviously enhanced. The reasons for the enhancement of luminescence are due to improved crystallization after S doping and the relatively large electronegativity difference between S and Mo. Additionally, the coincidence of the excitation wavelength with the emission of GaN chips may recommend this phosphor system as a potential candidate for use in white light-emitting diodes.     

The absorption and emission properties of highly transparent ZrO2-doped Yb3+: Y2O3 ceramics

Ultra-highly transparent ZrO₂-doped Yb³⁺: Y₂O₃ ceramics were prepared by slip casting and vacuum pressureless sintering and the transmittance reached the highest value of 80.9% for the sample doped with 8.0 at% Yb³⁺. There are three main absorption peaks at 905, 950, and 976 nm, corresponding to the transition from the lowest level of field splitting of ²F_7/2 crystal to every splitting energy levels of ²F_5/2 crystal field. We analyzed the absorption and emission spectra of transparent Yb³⁺: Y₂O₃ from the energy level structure of Yb³⁺, and the transmission, absorption, and emission spectra were systematically studied. There are three main absorption peaks at 905, 950, and 976 nm and four emission peaks at 1076, 1031, 1013, and 977 nm, respectively. The emission peaks at 977 and 1013 nm broaden and vanish for 8.0 and 10.0 at% Yb³⁺-doped Y₂O₃, which may be related to the change of Y₂O₃ crystal field caused by high concentration.     

Red-emitting enhancement of Bi4Si3O12:Sm3+ phosphor by Pr3+ co-doping for White LEDs application

In this account, Bi₄Si₃O₁₂:Sm³⁺ and (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) red phosphors were prepared by solution combustion method fueled by citric acid at 900 °C for 1 h. The effects of co-doping Pr³⁺ ions on red emission properties of Bi₄Si₃O₁₂:Sm³⁺ phosphors, as well as the mechanism of interaction between Sm³⁺ and Pr³⁺ ions were investigated by various methods. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) revealed that smaller amounts of doped rare earth ions did not change the crystal structure and particle morphology of the phosphors. The photoluminescence spectroscopy (PL) indicated that shape and position of the emission peaks of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at λ_ex=403 nm were similar to those of Bi₄Si₃O₁₂:Sm³⁺ phosphors. The strongest emission peak was recorded at 607 nm, which was attributed to the ⁴G_5/2→⁶H_7/2 transition of the Sm³⁺ ion. The photoluminescence intensities of Bi₄Si₃O₁₂:Sm³⁺ phosphors were significantly improved by co-doping with Pr³⁺ ions and were maximized at Sm³⁺ and Pr³⁺ ions doping concentrations of 4 mol% and 0.1 mol%, respectively. The characteristic peaks of Sm³⁺ ions were displayed in the emission spectra of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at respectively λ_ex=443 nm and λ_ex=481 nm (Pr:³H₄→³P₂, ³H₄→³P₀). This indicated the existence of Pr³⁺→Sm³⁺ energy transfer in (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors.     

Scintillation and dosimeter properties of CaF2 transparent ceramics doped with Nd3+ produced by SPS

We have developed CaF₂:Nd transparent ceramics with varying doping concentrations of Nd by spark plasma sintering (SPS) and evaluated the optical, scintillation and dosimeter properties. The samples showed effective absorption peaks in the visible and near infrared regions due to the 4f-4f transitions of Nd³⁺. In scintillation properties, Nd³⁺ was also active and showed the 4f-4f radiative transitions of Nd³⁺ which appeared at 860 and 1064 nm under X-ray irradiation. In photoluminescence under 160 nm excitation, the samples showed emission peaks in the vacuum ultraviolet region due to the 5d-4f transitions of Nd³⁺. Furthermore, the samples showed thermally stimulated luminescence (TSL) exhibiting glow peaks at 100, 150 and 380 °C. Among the present samples the 5% Nd-doped sample showed the highest sensitivity which allowed to measure radiation dose from 0.1 to 1000 mGy with a good linear response.     

Effects of Nd Concentration on Microstructure and Optical Properties of Nd: CaF2 Transparent Ceramics

Highly transparent Nd‐doped calcium fluoride (Nd: CaF₂) ceramics with different Nd‐doped concentrations were fabricated by hot‐pressed method using Nd: CaF₂ nanopowders synthesized by coprecipitation method. SEM observations indicated that the average grain size of nanopowders was about 16–30 nm and the average grain size of the ceramics was between 200 nm and 1 μm. The grain boundaries of the ceramics were clean and no pores or impurities were detected. For 2‐mm‐thickness sample, the transmittance of the as‐fabricated 5 at.% Nd: CaF₂ ceramic at 1200 nm was about 85%. The absorption coefficient and emission intensity of the Nd: CaF₂ ceramics were measured and discussed. From the Nd: CaF₂ ceramics fluorescent spectra and the decay curves, it was found that the fluorescent quenching effect became more evident with the increase in the Nd³⁺ ions‐doped concentration.     

Highly transparent Yb:Y2O3 ceramics obtained by solid-state reaction and combined sintering procedures

(Y_0.87-xLa_0.1Zr_0.03Yb_x)₂O₃ (x?=?0.02, 0.04, 0.05) transparent ceramics were obtained by solid-state reaction and combined sintering procedures with La₂O₃ and ZrO₂ as sintering additives. A method based on two-step intermediate sintering in air followed by vacuum sintering was applied in order to control the densification and grain growth of the samples during the final sintering process. The results indicate that La₂O₃ and ZrO₂ co-additives can improve the microstructure and optical properties of Yb:Y₂O₃ ceramics at relatively low sintering temperature. On the other hand, the addition of Zr⁴⁺ ions leads to the formation of dispersed scattering volumes in the ceramic bodies. Transmittance of 78.8% was measured for the 2.0?at% Yb:Y₂O₃ ceramic sample at the wavelength of 1100?nm. The spectroscopic properties of Yb:Y₂O₃ ceramics were investigated at room temperature. The obtained results show that the absorption cross-section at 978?nm is in the range of 2.08?×?10^–20 to 2.36?×?10^–20 cm², whereas the emission cross-section at 1032?nm is ~1.0?×?10^–20 cm².     

Cathodoluminescence mapping and thermoluminescence of Pr3+ doped in a CaTiO3/CaGa2O4 composite phosphor

In order to probe the properties of the one pot prepared composite phosphor of CaTiO₃ and CaGa₂O₄, cathodoluminescence mapping, thermoluminescence and lifetime measurements were carried out. The structural study showed both irregular and rod shaped particles, which match with CaTiO₃ and CaGa₂O₄, respectively, according the x-ray maps. The cathodoluminescence spectrum showed emission peaks from ³P₀→³H₄ and ¹D₂→³H₄ transitions, with the earlier transition completely absent in CaTiO₃:Pr emission at room temperature. The diffuse reflectance spectrum showed a shifted band of the inter-valence charge transfer from 360 nm to 388 nm, which is not observable for CaTiO₃:Pr³⁺and CaGa₂O₄:Pr³⁺. Additionally, the phosphorescence decay curve was recorded and the presence of electron trapping centers was confirmed using thermoluminescence spectroscopy.     

Pr3+/Yb3+:PLZT ferroelectric ceramics for near‐infrared radiation at 1340 nm

The near‐infrared luminescence properties of Pr³⁺/Yb³⁺:PLZT ferroelectric ceramics have been examined for the first time. Independently, upon either 450 nm (Pr³⁺) or 980 nm (Yb³⁺) excitation, luminescence centered at 1340 nm was observed, which corresponds to the ¹G₄→³H₅ transition of Pr³⁺. Several spectroscopic parameters for the ¹G₄→³H₅ transition of Pr³⁺ ions were determined. The average product of emission cross section and radiative lifetime were relatively large for all x/65/35 PLZT samples (x=6‐10) studied, with values close to 105±2 (×10^?26 cm²·s). These spectroscopic investigations indicate that Pr³⁺/Yb³⁺:PLZT ferroelectric ceramics are promising candidate for efficient sources emitting near‐infrared radiation at 1340 nm.