Pr:YAG temperature imaging in gas-phase flows

In this study, a new thermographic phosphor for planar gas-phase thermometry is investigated. The thermographic phosphor used is composed of trivalent praseodymium (Pr³⁺) ions doped into a yttrium aluminum garnet (YAG) host. Spectrally-resolved emission data were taken in a furnace for temperatures up to 1,300 K. The emission spectra were used to develop a temperature measurement strategy utilizing a non-equilibrium population ratio. The developed temperature measurement technique was demonstrated in a turbulent heated air jet for exit temperatures ranging from 300 to 750 K. The results demonstrate the promise of the Pr:YAG phosphor for obtaining high-precision single-shot temperature measurements in gas-phase flows.     

Low thermal quenching and high-efficiency Ce, Tb-co-doped Ca3Sc2Si3O12 green phosphor for white light-emitting diodes

Low thermal quenching and high-efficiency Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSSO:Ce³⁺) phosphors with co-doping Tb³⁺ ion were prepared by a solid state method and the properties of these phosphors were investigated. The results showed that co-doping of Tb³⁺ not only enhances the photoluminescence remarkably and decreases the thermal quenching of the phosphor, but also heightens the performances of the LEDs fabricated with the phosphor. A high-efficiency and low color temperature white LED was fabricated with the prepared CSSO:1%Ce³⁺, 0.5%Tb³⁺ and a red phosphor, indicating that CSSO:1%Ce³⁺,0.5%Tb³⁺ phosphor is a suitable green phosphor for the fabrication of high-efficiency white LEDs.     

Effect of Ce co-doping on KY3F10:Pr crystals

A spectroscopic investigation on the effect of Ce³⁺ co-doping in fluoride KY₃F₁₀:Pr³⁺ crystals is presented. In particular spectroscopic measurements of three different samples of KY₃F₁₀ crystal doped with 0.3at% Pr³⁺ and co-doped with 0at%, 0.17at% and 0.3at% Ce³⁺ are discussed. Details on the growth of the crystals are also reported. Measurements were performed in the temperature range 10-300 K. Fluorescence and lifetime measurements have shown a cross relaxation between ³P₀-¹D₂ levels of Pr³⁺ and ²F_7/2-²F_5/2 of Ce³⁺. Data exhibit that this effect is strictly related to the Cerium concentration.     

The luminescence and energy transfer in Pr3+–Ce3+ co-doped Lu0.8Sc0.2BO3 crystals

Lu_0.8Sc_0.2BO₃ crystals doped with 1 at%Ce³⁺ and co-doped 0.1 at% and 0.5 at%Pr³⁺ were grown by the Czochralski method. The concentrations of Pr³⁺ and Ce³⁺ in crystals were measured by the ICP-AES method. Absorption spectra, VUV–UV spectra, fluorescence decay time and X-ray excitation luminescence spectra were investigated at room temperature. The excitation luminescence spectra of Ce³⁺ emission and decay curves from the lower excited state levels of the 4f¹5d¹ and 5d¹ electronic configurations of the Pr³⁺ and Ce³⁺ conspicuously indicated the non-radiative energy transfer from Pr³⁺ to Ce³⁺. The detailed pathways were shown in the energy level diagram of the respective Ce³⁺ and Pr³⁺ in Lu_0.8Sc_0.2BO₃ host. In addition, the scintillation efficiency data indicated that the energy transfer effect is directly associated with the Pr³⁺ concentration.     

Energy transfer-based spectral properties of Tb-, Pr-, or Sm-codoped YAG:Ce nanocrystalline phosphors

Tb³⁺-, Pr³⁺-, or Sm³⁺-codoped YAG:Ce nanocrystalline phosphors were prepared using a modified polyol process. Possible tunability of Ce³⁺-related yellow emission in codoped YAG:Ce nanocrystalline systems was investigated. Dual emission of yellow and red spectral component with a single excitation wavelength was observed from YAG:Ce, Pr or YAG:Ce,Sm codoped systems via an energy transfer from Ce³⁺ and Pr³⁺ or Sm³⁺ ion. It was also observed that the energy transfer event in YAG:Ce, Pr nanocrystalline phosphor occurs mutually between Ce³⁺↔Pr³⁺, while in YAG:Ce, Sm and YAG:Ce, Tb the energy transfer progresses one way. The detailed pathways for transferring an excitation energy are explained based on the energy level diagrams of respective Ce³⁺, Pr³⁺, Sm³⁺, Tb³⁺ ion.     

Luminescence of KCaSO4Cl:X, Y (X=Eu or Ce; Y=Dy or Mn) halosulfate material

Polycrystalline KCaSO₄Cl:Eu, Dy, KCaSO₄Cl:Ce, Dy and KCaSO₄Cl:Ce, Mn phosphors prepared by a solid state diffusion method have been studied for its photoluminescence (PL) characteristics. The presence of two overlapping bands at around 400 and 450 nm in the PL emission spectra of the phosphor suggests the presence of Eu²⁺ in the host compound occupying two different lattice sites. The effects of co-doping on the photoluminescence (PL) characteristics of KCaSO₄Cl:Eu or Ce phosphors have been studied. The decrease in peak intensity of the phosphor on co-doping it with Dy gives an insight into the emission mechanism of the phosphors, which involves energy transfer from Eu²⁺→Dy³⁺, Ce³⁺→Dy³⁺ and Ce³⁺→Mn²⁺.     

Low temperature quenching and high efficiency Tm, La or Tb co-doped CaSc2O4:Ce phosphors for light-emitting diodes

Low temperature quenching and high efficiency CaSc₂O₄:Ce³⁺ (CSO:Ce³⁺) phosphors co-doped with Tm³⁺, La³⁺ and Tb³⁺ ions were prepared by a solid state method and the phase-forming, morphology, luminescence and application properties of these phosphors were investigated. The results showed that co-doping of Tm³⁺, La³⁺ and Tb³⁺ ions can improve the luminescence properties and decrease temperature quenching of CSO:Ce³⁺ phosphor remarkably. High efficiency green-light-emitting diodes were fabricated with the prepared phosphors and InGaN blue-emitting (∼460 nm) chips. The good performances of the green-light-emitting LEDs made from co-doped CSO:Ce³⁺ phosphors confirm the luminescence enhancement and indicate that Tm³⁺, La³⁺ and Tb³⁺ co-doped CSO:Ce³⁺ phosphors are suitable candidates for the fabrication of high efficiency white LEDs.     

Investigations on acceptor (Pr3+) and donor (Nb5+) doped cerium oxide for the suitability of solid oxide fuel cell electrolytes

Nanocrystalline acceptor (Pr³⁺) and donor (Nb⁵⁺) doped cerium oxide are synthesized by sol-gel method via hydrolysis process and evaluated for the suitability of applying as an electrolyte for the intermediate temperature solid oxide fuel cells. Phase purity and crystallite size of the synthesized materials are ascertained by powder X-ray diffraction studies. Introduction of Pr³⁺ ions in the cerium lattice exhibited a lower crystallite size than the Nb⁵⁺, which exposes the probability to attain high oxide ion conductivity of Pr³⁺ doped cerium oxide. Fourier transform infrared and Raman spectra confirm the functional groups and formation of Pr³⁺ and Nb⁵⁺ ions in the cerium lattice. Absorbance spectra exhibit the charge-transfer transition from O²⁻ (2p) to Ce⁴⁺ (4f) orbital in cerium oxide. Pr³⁺ and Nb⁵⁺ ions doped cerium lattice create the oxygen vacancies and favor the formation of Ce³⁺ from Ce⁴⁺. Valence band transition of Ce³⁺ ions from the 5d to 4f levels are examined by photoluminescence studies. The morphological features of Ce-Pr-O and Ce-Nb-O are investigated by scanning and transmission electron microscopy. Electrochemical impedance spectroscopy is used to analyze the conductivity properties of solid electrolytes. Ce-Pr-O shows the high oxide ion conductivity of 0.1 S/cm at 600 °C with an activation energy of 0.73 eV. Electrolytes with specific conductivities higher than 10⁻² S/cm at intermediate temperatures (∼400–600 °C) are required for solid oxide fuel cells to operate with less maintenance. Hence, Ce-Pr-O can be a suitable electrolyte material for intermediate temperature solid oxide fuel cells.

     

Recombination processes in lanthanum beryllate single crystals doped with Ce3+ and Pr3+ ions

The paper presents experimental results on recombination processes in lanthanum beryllate (BLO) single crystals (undoped BLO, and doped with 0.5 at % by Ce³⁺ and Pr³⁺ ions) obtained using XRL-spectroscopy at T = 8, 80 and 290 K and thermoluminescence technique in the temperature range of 8–650 K. The paper discusses spectra of the steady-state XRL-luminescence recorded in the energy range from 1.5 to 6.2 eV at different temperatures between 8 and 290 K; temperature dependences of XRL intensity recorded in the temperature range from 8 to 650 K; thermoluminescence glow curves recorded in spectral-integrated regime after X-ray exposure at T₀ = 8 or 290 K.     

Pr3+ luminescence center in Lu2Si2O7 host

Pr³⁺‐doped Lu₂Si₂O₇ (LPS:Pr) microcrystalline phosphor was prepared by the sol–gel method. We study the LPS:Pr luminescence properties under UV and X‐ray excitation within 80–500 K. The emission spectrum is dominated by fast 5d–4f band peaking at 261 nm having 16 ns decay time. By purely optical contactless methods we determine the energy barrier of 300 meV for thermal ionization of the Pr³⁺ 5d₁ relaxed excited state in LPS host. The barrier is high enough to keep the room temperature quantum efficiency of the Pr³⁺ luminescence center close to unity. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhancement of red spectral emission intensity of Y3Al5O12:Ce phosphor via Pr co-doping and Tb substitution for the application to white LEDs

We have enhanced color-rendering property of a blue light emitting diode (LED) pumped white LED with yellow emitting Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) phosphor using addition of Pr and Tb as a co-activator and host lattice element, respectively. Pr³⁺ addition to YAG:Ce phosphor resulted in sharp emission peak at about 610 nm through ¹D₂→³H₄ transition. And when Tb³⁺ substituted Y³⁺ sites, Ce³⁺ emission band shifted to a longer wavelength due to larger crystal field splitting. Y₃Al₅O₁₂:Ce³⁺, Pr³⁺ and (Y_1−xTb_x)₃Al₅O₁₂:Ce³⁺ phosphors were coated on blue LEDs to fabricate white LEDs, respectively, and their color-rendering indices (CRIs, R_a) were measured. As a consequence of the addition of Pr³⁺ or Tb³⁺, CRI of the white LEDs improved to be R_a=83 and 80, respectively. Especially, blue LED pumped (Y_0.2Tb_0.8)₃Al₅O₁₂:Ce³⁺ white LED showed both strong luminescence and high color-rendering property.     

Ca8Mg(SiO4)4Cl2:Ce3+, Tb3+: A potential single-phased phosphor for white-light-emitting diodes

A single-phased white-light-emitting phosphor Ca₈Mg(SiO₄)₄Cl₂:Ce³⁺, Tb³⁺ (CMSC:Ce³⁺, Tb³⁺) is synthesized by a high temperature solid-state reaction method, and its photoluminescence properties are investigated. The obtained phosphor exhibits a strong excitation band between 250 and 410 nm, matching well with the dominant emission band of a UV light-emitting-diode (LED) chip. Energy transfer from Ce³⁺ to Tb³⁺ ions has been investigated and demonstrated to be a resonant type via a dipole–dipole mechanism. The energy transfer efficiency as well as the critical distance is also estimated. Furthermore, the phosphors can generate light from yellow-green through white and eventually to blue by properly tuning the relative ratio of Ce³⁺ to Tb³⁺ ions grounded on the principle of energy transfer. The results show that this phosphor has potential applications as a single-phased phosphor for UV white-light LEDs.     

Photoluminescence characteristics of Pr3+ in ThO2: interplay of defects in a photo-induced charge transfer

Photo-luminescence studies of Pr³⁺ activated thorium oxide phosphor have revealed that mainly ³P→³H₄ and ¹D₂→³H₄ transitions with life-time of 30 and 600 μs are observed in this sample. An exponential reduction in the emission intensity of Pr³⁺ ions was observed on following continuous excitation with 275 nm corresponding to the f–d transition band of Pr³⁺ ions. Such a reduction in emission intensity was observed at all temperatures investigated in the range 90–330 K. The emission intensity recovered partially on dark storage only above 180 K. The recovery of emission intensity was also observed on the illumination of pre-exposed sample to light in the wavelength region 300–430 nm. Following illumination with 275 nm, Pr³⁺ activated thorium oxide phosphor has displayed a weak thermally stimulated luminescence. These results thus suggest that the optical excitation dynamically changes the state of the system under observation, and that changes are occurring in the valence state of Pr ions due to e/h transfer process on 275-nm exposure. On dark storage and also on 365-nm illumination of the pre-exposed sample, e/h traps recombine to cause emission signal recovery. The analysis of data on reduction in intensity obtained with exposure to 275 nm suggests the likelihood of the of Pr³⁺ ions existing at three different sites. The activation energies associated with the release of electrons from excited Pr³⁺ ions at different sites were determined from the temperature dependence of the photo-induced charge transfer process.     

Enhanced luminescence and degradation of SiO2:Ce,Tb powder phosphors prepared by a sol-gel process

Enhanced green photoluminescence and cathodoluminescence (CL) from Tb³⁺ ions due to co-doping with Ce³⁺ ions were observed from SiO₂:Ce,Tb powder phosphors prepared by a sol-gel technique. Blue emission from the Ce³⁺ ions was completely suppressed by Tb co-doping, presumably due to energy transfer from Ce³⁺ to Tb³⁺. In addition, the green CL intensity from SiO₂:Ce,Tb degraded by ∼50% when the powders were irradiated for 10 h with a 2 keV, 54 mA/cm² beam of electrons in an ultra-high vacuum chamber containing either 1×10⁻⁸ or 1×10⁻⁷ Torr O₂. Desorption of oxygen from the surface was observed during the decrease of CL intensity. The mechanisms for energy transfer from Ce³⁺ ions to Tb³⁺ ions to enhance the green luminescence, and mechanisms for desorption of oxygen from the phosphor surface that would result in decreased CL intensity are discussed.     

Influence of lead-related centers on luminescence of Ce3+ and Pr3+ centers in single crystalline films of aluminium perovskites and garnets

Luminescence characteristics of Ce³⁺- and Pr³⁺-doped aluminium perovskite (LuAlO₃, YAlO₃) and garnet (Lu₃Al₅O₁₂, Y₃Al₅O₁₂) single crystalline films, prepared by the liquid phase epitaxy method with the use of the PbO-based flux, were investigated by the time-resolved spectroscopy methods in the 80–300 K temperature range. The influence of various lead-related centers on the characteristics of the Ce³⁺- and Pr³⁺-related luminescence centers was studied. It was found that the presence of lead-related centers in the single crystalline films results in a decrease of the quantum efficiency and appearance of undesirable slow components in the luminescence decay kinetics. The possibilities of improving the scintillation characteristics of the single crystalline films were considered.     

Luminescence spectroscopy of Ce3+-doped ABaPO4 (A=Li, Na, K) phosphors

Ce³⁺ doped ABaPO₄ (A=Li, Na, K) phosphors were prepared by conventional high temperature solid-state reaction. The phosphors were investigated by XRD, photoluminescence excitation and emission spectra, and luminescence decay curves. The five 5d levels corresponding to the 4f¹→4f⁰5d¹ transition of Ce³⁺ ions were identified. The spectroscopic parameters, e.g., the 5d barycenter, the crystal-field splitting, and the Stokes shift, were discussed. LiBaPO₄:Ce³⁺ phosphor could be efficiently excited by the near-UV lights (330–420 nm) and showed a broad emission band in the range of 430–620 nm with the maximum wavelength at 468 nm. In contrast, Ce³⁺-doped NaBaPO₄ and KBaPO₄ showed only excitation bands in a limited UV region (230–370 nm) and have blue emission at 385 nm and 416 nm, respectively. The temperature quenching of luminescence and the chromaticity coordinates were reported. The luminescence properties were discussed by analyzing the crystal structure and the local surroundings of Ce³⁺ ions on the Ba²⁺ sites.     

Combustion synthesis of YAG:Ce and related phosphors

YAG:Ce is an important phosphor having applications in various fields ranging from solid state lighting to scintillation detectors. YAG phosphors doped with activators are mainly synthesized by solid state reaction techniques that require high sintering temperatures (above 1500°C) to eliminate YAM and YAP phases. Though several soft chemical routes have been explored for synthesis of YAG, most of these methods are complex and phase pure materials are not obtained in one step, but prolonged annealing at temperatures around 1000°C or above become necessary. One step combustion synthesis of YAG:Ce³⁺ and related phosphors carried out at 500°C furnace temperature is reported here. Activation with Ce³⁺ could be achieved during the synthesis without taking recourse to any post-combustion thermal treatment. LEDs prepared from the combustion synthesized YAG:Ce³⁺, exhibited properties comparable to those produced from the commercial phosphor.     

Dyand Mn emission in KMgSO4Cl phosphor

In the present paper, KMgSO₄Cl:Ce³⁺, KMgSO₄Cl:Ce³⁺,Dy³⁺, and KMgSO₄Cl:Ce³⁺,Mn²⁺, new halosulphate phosphors were synthesized by wet chemical method. X-ray powder diffraction (XRD) and photoluminescence (PL) characterization of phosphors have been reported in this paper. The effects of Dy³⁺ co-doping on the PL characteristics of KMgSO₄Cl:Ce phosphor were studied. Energy transfer from Ce³⁺→Dy³⁺and Ce³⁺→Mn²⁺ results in increase in PL peak intensity suggesting that Ce³⁺ plays an important role in PL emission in the present matrix. The PL emission spectra have two peaks (482 and 571 nm) and a single peak (564 nm), which could be attributed to the Ce³⁺→Dy³⁺and Ce³⁺→Mn²⁺ emissions, respectively.     

The effect of codopants on spectral-kinetic characteristics of luminescence of scintillation glasses doped with terbium ions

The effect of Ce³⁺ and Pr³⁺ ions on spectral-kinetic characteristics of luminescence of lithium–phosphate–borate glasses is studied. It is shown that terbium ion luminescence caused by transitions from ⁵D₃ and ⁵D₄ multiplets to the ground 7FJ term is detected in samples containing Tb³⁺/Ce³⁺ and Tb³⁺/Pr³⁺. It has been found that an increase in the concentration of cerium ions from 0.2 to 1 wt % leads to an increase in the intensity of main luminescence bands of terbium ions. In Tb³⁺/Pr³⁺ glasses, a decrease in the relative light yield is observed with an increase in the concentration of Pr³⁺ ions. Processes of energy transfer between Tb³⁺/Ce³⁺ and Tb³⁺/Pr³⁺ ions are discussed.     

Enhanced luminescence of Tb by efficient energy transfer from Ce in Sr2B5O9Cl host

Ce³⁺ and Tb³⁺ co-doped Sr₂B₅O₉Cl phosphors with intense green emission were prepared by the conventional high-temperature solid-state reaction technique. A broad band centered at about 315 nm was found in phosphor Sr₂B₅O₉Cl: Ce³⁺, Tb³⁺ excitation spectrum, which was attributed to the 4f-5d transition of Ce³⁺. The typical sharp line emissions ranging from 450 to 650 nm were originated from the ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions. The photoluminescence (PL) intensity of green emission from Tb³⁺ was enhanced remarkably by co-doping Ce³⁺ in the Tb³⁺ solely doped Sr₂B₅O₉Cl phosphor because of the dipole-dipole mechanism resonant energy transfer from Ce³⁺ to Tb³⁺ ions. The energy transfer process was investigated in detail. In light of the energy transfer principles, the optimal composition of phosphor with the maximum green light output was established to be Sr_1.64Ce_0.08Tb_0.1Li_0.18B₅O₉Cl by the appropriate adjustment of dopant concentrations. The PL intensity of Tb³⁺ in the phosphor was enhanced about 40 times than that of the Tb³⁺ single doped phosphor under the excitation of their optimal excitation wavelengths.