Co-doped Ca Research Articles

Photoluminescence properties and energy transfer in the Sm3+ and Eu3+ co-doped Ca3Bi(PO4)3 red phosphor

Red phosphors play a vital role in improving the color quality and luminous efficiency of white light-emitting diodes (w-LED). However, it is still a challenge to develop red phosphors with higher efficiency, higher color purity, and better matching near-ultraviolet (n-UV) chips. In this paper, a series of Sm3+, Eu3+ co-doped Ca3Bi(PO4)3 (CBP) were successfully prepared by the high temperature solid-state reaction method. The crystal structure, photoluminescence properties, and energy transfer mechanism were investigated in detail. The maximum doping concentration of Eu3+ in CBP was confirmed to be 30 mol% in this research considering the structural instability with higher doping concentration. Under 393 nm n-UV excitation, CBP: 8 mol% Sm3+, 25 mol% Eu3+ phosphor exhibit excellent red-lighting emission at 612 nm with high color purity of 99.28 %. More impressively, the effective excitation wavelength of Sm3+, Eu3+ co-doped CBP phosphors is extended to 391–403 nm due to energy transfer from Sm3+ to Eu3+. Moreover, the energy transfer mechanism is rationalized through dipole–dipole interaction as indicated via decay kinetics studies. The fabricated w-LED emits white light, which has high color rendering index (CRI = 86.0) at color coordinate temperature CCT = 6985 K and luminous efficiency (66 lm/w). The phosphor shows excellent thermal stability, and the fluorescence intensity to temperature 423 K can retain 75.98 % of its initial value of room temperature. These results indicate that this phosphor with high-efficiency red-emitting is a promising candidate as a red component for n-UV LED application.

Upconversion luminescence Ca–Mg–Si bioactive glasses synthesized using the containerless processing technique

In this study, a series of Er3+/Yb3+ co-doped Ca–Mg–Si glasses were prepared via the containerless processing. Phase composition and luminescent properties of the prepared materials were investigated through XRD and spectrometry, and bioactivity, biocompatibility and cytotoxicity were evaluated. The XRD patterns indicated that akermanite (AKT) ceramic powders were completely transformed into the glassy phase (AKT-G, EYA) through the containerless processing, which exhibit upconversion luminescence, and the luminescence intensity increased with the increase of the doping amount of Er3+ and Yb3+. High amount of Yb3+ doping and existence of Ca2+ in glasses resulted in more intensive red-light emission. The SEM observation, combined with EDS analysis, and cell culture experiments showed that the as-prepared glasses were nontoxic, biocompatible and bioactive. All these results demonstrated that the containerless processing is a facile method for preparing homogeneous luminescent bioactive glasses. Furthermore, this luminescent Ca–Mg–Si glasses may be used as bone implant materials to study the in vivo distribution of degradation products of bone implants, which may be of great significance for the development and clinical application of new bone grafting materials.

Near-infrared quantum cutting of Dy3+, Ho3+–Yb3+ and Er3+–Yb3+-doped Ca10K(PO4)7 phosphors

Dy 3+, Ho 3+– Yb 3+ and Er 3+– Yb 3+-doped Ca 10 K ( PO 4)7 phosphors were prepared by solid-state reaction method, and their luminescence properties of near-infrared (NIR) quantum cutting (QC) were investigated for the first time. The Rietveld refinement performed for the X-ray diffractometer (XRD) data indicates the obtained samples are single-phase. From the excitation spectra, it can be seen that the energy transfers from Ho 3+ to Yb 3+, and from Er 3+ to Yb 3+ occur. The Dy 3+, Ho 3+– Yb 3+ and Er 3+– Yb 3+ co-doped Ca 10 K ( PO 4)7 samples all exhibit NIR emission peaks in the QC processes, and their spectral characteristics are agreement with the corresponding NIR QC mechanisms. The NIR QC properties of the as-prepared samples indicate the potential applications in modifying the solar spectrum to enhance the efficiency of silicon solar cells.

Photoluminescence properties of emission-tunable Ca 9Y(PO 4) 7: Tm 3+, Dy 3+ phosphor for white light emitting diodes

A white-emitting Ca 9Y(PO 4) 7: Tm 3+, Dy 3+ phosphor has been successfully prepared by conventional high-temperature solid-state reaction. X-ray diffraction (XRD) and fluorescence spectrophotometer were used to characterize the as-synthesized phosphors. The excitation and emission spectra show that all the Tm 3+ and Dy 3+ co-doped Ca 9Y(PO 4) 7 samples can be effectively excited by UV light and then emit blue and yellow light simultaneously. Furthermore, the emission and color coordinate of as-obtained samples pumped by 365 nm are able to be adjusted around white light by varying the doping concentrations of Tm 3+ and Dy 3+. So, the as-fabricated single-composition Ca 9Y(PO 4) 7: Tm 3+, Dy 3+ phosphor will have a promising application in the area of white light emitting diodes.

Near-ultraviolet excitable Ca 4Y 6(SiO 4) 6O: Ce 3+, Tb 3+ white phosphors for light-emitting diodes

The present investigation aims to demonstrate the potentiality of Tb 3+ and Ce 3+ co-doped Ca 4Y 6(SiO 4) 6O phosphors. By incorporation of Ce 3+ into Ca 4Y 6(SiO 4) 6O: Tb 3+, the excitation band was extended from short-ultraviolet to near-ultraviolet region. The energy transfer from Ce 3+ to Tb 3+ in Ca 4Y 6(SiO 4) 6O host was investigated and demonstrated to be a resonant type via a dipole–dipole mechanism with the critical distance of 10.2 Å. When excited by 352 nm, Ca 4Y 6(SiO 4) 6O: Ce 3+, Tb 3+ exhibited a brighter and broader violet-blue emission (421 nm) from the Ce 3+ and an intense green emission (542 nm) from the Tb 3+. Combining the two emissions whose intensities were adjusted by changing the doping levels of the co-activator, an optimized white light with chromaticity coordinates of (0.278, 0.353) is generated in Ca 4Y 6(SiO 4) 6O: 2% Ce 3+, 8% Tb 3+, and this phosphor could be potentially used in near-ultraviolet light-emitting diodes.

Intense green/yellow emission in Ca 8Zn(SiO 4) 4Cl 2:Eu 2+, Mn 2+ through energy transfer for blue-LED lighting

Eu 2+ and Mn 2+ co-doped Ca 8Zn(SiO 4) 4Cl 2 phosphors have been synthesized by a high temperature solid state reaction. Energy transfer from Eu 2+ to Mn 2+ is observed. The emission spectra of the phosphors show a green band at 505 nm of Eu 2+ and a yellow band at 550 nm of Mn 2+. The excitation spectra corresponding to 4f 7-4f 65d transition of Eu 2+ cover the spectral range of 370–470 nm, well matching UV and/or blue LEDs. The shortening of fluorescent lifetimes of Eu 2+ followed by simultaneous increase of fluorescent intensity of Mn 2+ with increasing Mn 2+ concentrations is studied based on energy transfer. Upon blue light excitation the present phosphor can emit intense green/yellow in comparison with other chlorosilicate phosphors such as Eu 2+ and Mn 2+ co-doped Ca 8Mg(SiO 4) 4Cl 2 and Ca 3SiO 4Cl 2, demonstrating a potential application in phosphor converted white LEDs.

Luminescence properties of Ca0.65La0.35F2.35:Yb3+, Er3+ with enhanced red emission via upconversion

Under 980 nm excitation, Ca 0.65 La 0.35 F 2.35 :20 mol.%Yb 3+ , x Er 3+ showed intense red upconversion luminescence, which was ascribed to 4 F 9/2 → 4 I 15/2 transition of Er 3+ . The ground-state absorption (GSA), excited-state absorption (ESA) and energy transfer (ET) processes between Er 3+ /Yb 3+ ions and Er 3+ /Er 3 ions were involved in the enhanced red emission mechanism. . ▶ Yb 3+ /Er 3+ codoped Ca 0.65 La 0.35 F 2.35 materials with intense red emission via upconversion were prepared by a high temperature solid-state method. ▶ Ca 0.65 La 0.35 F 2.35 :20 mol.%Yb 3+ , x Er 3+ showed intense red upconversion luminescence, which was ascribed to 4 F 9/2 → 4 I 15/2 transition of Er 3+ . ▶ The green and red emissions are two-photon processes, while both energy transfers between Yb 3+ /Er 3+ and Er 3+ /Er 3+ are involved in the red emission mechanism of the Ca 0.65 La 0.35 F 2.35 :20 mol.%Yb 3+ , x Er 3+ materials. Yb 3+ /Er 3+ codoped Ca 0.65 La 0.35 F 2.35 materials with intense red emission via upconversion were prepared by a high temperature solid-state method. Based on the upconversion luminescence properties investigations, it was found that, under 980 nm excitation, Ca 0.65 La 0.35 F 2.35 :20 mol.%Yb 3+ , x Er 3+ showed intense red upconversion luminescence, which was ascribed to 4 F 9/2 → 4 I 15/2 transition of Er 3+ , although both green and red emissions could be detected. It was also found that the green and red emissions originated the two photon processes, and the ground-state absorption (GSA), excited-state absorption (ESA) and energy transfer (ET) processes between Er 3+ /Yb 3+ ions and Er 3+ /Er 3 ions were involved in the enhanced red emission mechanism.

Photoluminescence of double-color-emitting phosphor Ca 5(PO 4) 3Cl:Eu 2+, Mn 2+ for near-UV LED

Eu 2+ activated Ca 5(PO 4) 3Cl blue-emitting phosphors were prepared by the conventional solid state method using CaCl 2 as the chlorine source and H 3BO 3 as flux. The structure and luminescent properties of phosphors depend on the concentrations of Eu 2+, the amount of CaCl 2 and the usage of the H 3BO 3 flux were investigated systematically. Eu 2+ and Mn 2+ Co-doped Ca 5(PO 4) 3Cl with blue and orange double-band emissions were also researched based on the optimal composition and synthesis conditions. The energy transfer between Eu 2+ and Mn 2+ was found in the phosphor Ca 5(PO 4) 3Cl:Eu 2+, Mn 2+, and the Co-doped phosphor can be efficiently excited by near-UV light, indicating that the phoshor is a potentional candidate for n-UV LED used phosphor.

Electrode properties of Co-doped Ca 2Fe 2O 5 as new cathode materials for intermediate-temperature SOFCs

Brownmillerite oxide Ca 2Fe 2− x Co x O 5 ( x = 0.2, 0.4, 0.6) was characterized by XRD, SEM and electrochemical impedance spectrum (EIS), respectively. Ca 2Fe 2− x Co x O 5 has no reaction with Sm 0.2Ce 0.8O 1.9 (SDC) electrolyte at 1100 °C for 10 h in air. The thermal expansion coefficient (TEC) of Ca 2Fe 2− x Co x O 5 increased with increasing Co content, and the TEC value was compatible with SDC. The electrode properties of Ca 2Fe 2− x Co x O 5 were studied under various temperatures and oxygen partial pressures. The polarization resistance ( R p) of Ca 2Fe 2− x Co x O 5 with x = 0.2, 0.4 and 0.6 are 0.23, 0.48 and 1.05 Ω cm 2 at 700 °C in air, respectively. The rate-limiting step for oxygen reduction reaction was the charge transfer process. Ca 2Fe 1.8Co 0.2O 5 cathode exhibits the lowest overpotential of about 50 mV at a current density of 70 mA cm −2 at 700 °C in air.

Chromium(IV) Stabilisation in New Ceramic Matrices by Coprecipitation Method: Application as Ceramic Pigments

In this paper the stabilization of Cr4+ in new ceramic matrices as willemite Zn2SiO4 and galium-gadolinium garnet GGG (Gd3Ga5O12) is studied and compared with the chromium-sphene ceramic pigment using the traditional solid reaction and an unconventional coprecipitation method.The chromate amount etched from the powders using CrIII and CrVI precursors on ceramic and coprecipitation routes are analysed in order to evaluate the environmental impact on the waste water. Cr-willemite and codoped Ca, Cr-GGG produces solid solutions of Cr4+ ion occupying tetrahedral and dodecahedral sites, respectively, while Cr4+ into sphene lattice occupies octahedral sites. Cr-willemite are stable when used as ceramic pigment in habitual tile glazes but Cr-GGG unstabilses and produces green colour associated to Cr3+ solved in the glaze. Coprecipitate powders are more reactive than ceramic powders but in Cr-GGG stabilizes the metastable Ca3Cr2O8 oxide. Chromate amount in washing hot water are not dependent of the chromium precursor but depends of the allowed reactivity level and the reaction media.

Spectroscopic properties of Er 3+, Yb 3+ and Er 3+/Yb 3+ doped metaphosphate glasses

The absorption and emission spectroscopies of Er 3+ doped and Er 3+/Yb 3+ codoped Ca(PO 3) 2, Sr(PO 3) 2 and Ba(PO 3) 2 glasses have been studied. From the Judd–Ofelt intensity parameters, the spontaneous emission probabilities of some relevant transitions and the radiative lifetimes of several excited states of Er 3+ have been calculated. The decay curves of the Er 3+ emission at 1.5 μm have been measured at different temperatures. The data have been fitted using a stretched exponential function and the obtained experimental lifetimes have been compared with the calculated radiative lifetimes. The difference between the experimental and calculated lifetimes is attributed to the presence of traces of OH groups in the host glasses. The absolute OH content in some glasses has been determined from the infrared spectra. The emission spectra at 1.5 μm of the Er 3+ ion in the codoped glasses have been measured at different temperatures. The integrated emission intensities decrease significantly on passing from room temperature to 13 K, suggesting a temperature dependence of the rate of the energy transfer process between Yb 3+ and Er 3+.