CaTiO3 Phosphors Research Articles

Upconversion, downshifting, quantum cutting and back energy trasfer from Yb3+ to Er3+ in Er3+/Yb3+ co-doped CaTiO3 phosphor, intense NIR generation for communication

The perovskite based phosphor materials are widely used to increase the efficiency of solar cells. In this work, Er3+ doped and Er3+/Yb3+ co-doped CaTiO3 perovskite phosphor samples have been synthesized by solid state reaction technique at 1473 K. The phosphor samples show orthorhombic phase with Pnma (62) space group. The average crystallites and particles size of CaTiO3 are increased in presence of Er3+ and Yb3+ ions. Er3+ doped CaTiO3 phosphor samples give downshifting emission under 379 nm excitation. Though upconversion emission is seen in Er3+ under 980 nm excitation without Yb3+ ions in this host. The emission intensity of Er3+ ion is enhanced by 46 and 16 times for green and red emissions, respectively in presence of Yb3+. An intense quantum cutting (QC) emission is observed at 980 nm in presence of Yb3+ in CaTiO3:0.5Er3+ phosphor under 379 nm excitation. The QC efficiency has been found to be 119 % for CaTiO3:0.5Er3+/5 Yb3+ phosphor. Further an interesting phenomenon of back energy transfer (BEnT) from Yb3+ to Er3+ giving an intense NIR emission from Er3+ at 1002 and 1550 nm have been observed. The phosphor sample also shows an intrinsic optical bistablity (IOB) by upconversion. Thus, the prepared phosphor samples may be useful to increase the efficiency of c-Si solar cell, NIR emission for communication, bistable material and green light emitting source.

Multicolor tunable emission through energy transfer in Dy3+/Ho3+ co-doped CaTiO3 phosphors with high thermal stability for solid state lighting applications

The exploration of multicolor emitting phosphors with single phase is extremely important for n-UV chip excited LED/WLED’s and multicolor display devices. In this paper, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials have been synthesized by solid state reaction method at 1473 K. The synthesized materials were characterized by XRD, FE-SEM, EDX, FTIR, PL and lifetime measurements. The PL emission spectra of Dy3+ doped CaTiO3 phosphors give intense blue and yellow emissions under UV excitation, while the PL emission spectra of Ho3+ doped CaTiO3 phosphor show intense green emission under UV/blue excitations. Further, to get the multicolor emission including white light, Dy3+ and Ho3+ were co-doped simultaneously in CaTiO3 host. It is found that alongwith colored and white light emissions, it also shows energy transfer from Dy3+ to Ho3+ with 367 nm and from Ho3+ to Dy3+ under 362 nm excitations. The energy transfer efficiency is found to be 67.76% and 69.39% for CaTiO3:4Dy3+/3Ho3+ and CaTiO3:3Ho3+/5Dy3+ phosphors, respectively. The CIE color coordinates, CCT and color purity of the phosphors have been calculated, which show color tunability from whitish to deep green via greenish yellow color. The lifetime of 4F9/2 level of Dy3+ ion and 5S2 level of Ho3+ ion is decreased in presence of Ho3+ and Dy3+ ions, respectively. This is due to energy transfer from Dy3+ to Ho3+ ions and vice versa. A temperature dependent photoluminescence studied of CaTiO3:4Dy3+/2Ho3+ phosphor show a high thermal stability (82% at 423 K of initial temperature 303 K) in the temperature range 303–483 K with activation energy 0.17 eV. The PLQY are 30%, 33% and 35% for CaTiO3:4Dy3+, CaTiO3:4Dy3+/2Ho3+ and CaTiO3:3Ho3+ phosphors, respectively. Hence, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials can be used in the field of single matrix perovskite color tunable phosphors which may be used in multicolor display devices, n-UV chip excited LED/WLED’s and photodynamic therapy for the cancer treatment.

Structure, photoluminescence properties, and energy transfer phenomenon in Sm3+/Eu3+ co-doped CaTiO3 phosphors

The energy transfer from Sm3+ and Eu3+ due to dipole–dipole interaction, variation in emission intensity of Sm3+ and Eu3+ peaks with varying concentration of Eu3+ and thermal stability of 2Sm3+, 2.5Eu3+ and 2Sm3+/2.5Eu3+ co-doped CaTiO3 phosphors.

Intense photoluminescence in CaTiO3:Sm3+ phosphors, effect of co-doping singly, doubly and triply ionized elements and their applications in LEDs.

In this work, Sm3+-doped and Sm3+/Li+/K+/Mg2+/Ba2+/Gd3+/Bi3+ co-doped CaTiO3 phosphors were synthesized by a solid-state reaction method at 1473 K. The phase of phosphors was identified to be orthorhombic with space group Pnma (62) by XRD measurements. The morphological properties of the prepared samples were studied by SEM measurements. The average crystallite and particle sizes were found to increase in the presence of modifiers and they follow the trend Li+ > Mg2+ > Gd3+ > K+ > Bi3+ > Ba2+. EDX measurements were used to verify the presence of Ca, Ti, O, Sm, K, Mg, Ba, Gd and Bi atoms in the prepared phosphor samples. The Sm3+ ion shows emission peaks at 564, 599 and 646 nm due to 4G5/2 → 6H5/2, 6H7/2 and 6H9/2 transitions upon 407 nm excitation, among which the peak situated at 599 nm has maximum emission intensity. Concentration quenching was observed above 2 mol% of Sm3+ ions in this host. However, the emission intensity of Sm3+ peaks can be enhanced using different modifier (Li+/K+/Mg2+/Ba2+/Gd3+/Bi3+) ions. It was found that the size (ionic radii) and charge compensation of the ion together play a dominant role. The enhancement is more after co-doping with smaller radius ions (Li+, Mg2+ and Gd3+), among which Li+ shows the largest enhancement. This is because ions of smaller size will be able to go closer to the activator ion and the charge imbalance causes a larger field. The CIE color coordinates, correlated color temperature (CCT) and color purity of the phosphors were calculated and show orange-red color emissions with a maximum color purity of ∼93% in the case of CaTiO3:2Sm3+/1.0Li+ phosphor. The lifetime value is increased in the presence of these ions. It is again maximum for the Li+ co-doped CaTiO3:2Sm3+ phosphor sample. Thus, the prepared phosphor samples are suitable sources for orange-red light.

White light emission via Pb2+ to Dy3+ energy transfer mechanism in CaTiO3 phosphor

CaTiO3 activated Pb2+ and Dy3+ with different doping concentrations were prepared by combustion technique. The prepared phosphors were characterized by XRD, SEM, and photoluminescence (PL) techniques. The Pb2+ doped CaTiO3 phosphor exhibits broad n-UV emission. The effect of varying Pb2+ doping concentration on PL result and critical transfer distance were studied. The PL spectra of CaTiO3:(Pb2+,Dy3+) exhibit characteristic Dy3+ emission in blue (483 nm) and yellow (578 nm) region. At higher concentration of Dy3+ in CaTiO3:(Pb3+,Dy3+) phosphor, efficient energy transfer occur from Pb2+ to Dy3+. The CIE chromaticity study showed CaTiO3:(Pb3+,Dy3+) phosphor emits light in white region, which can be useful white phosphor for ultraviolet convertible white-light emitting devices.

Locally-ordered A-site vacancy assisted photoluminescence enhancement in simply rare-earth doped perovskite oxide

An Sm3+and A-site vacancy doped CaTiO3phosphors, which demonstrate larger PL intensity than phosphors without vacancies. The formation of VAordering enables the exchange of charge between [Ca/VAOn] and [CaO12] clusters for enhanced PL properties.

Charge compensation assisted enhancement of photoluminescence in (Li+, Mg2+, Sr2+) doped CaTiO3: Eu/Dy/xGd for WLEDs applications

A series of CaTiO3: Eu3+, Eu3+/Dy3+, Eu3+/Dy3+/xGd3+, and Eu3+/Dy3+/Gd3+/M (M = Li+, Mg2+, Sr2+) perovskite micro phosphors have been prepared via solid-state reaction method. The structural, morphological, and spectral properties were systematically characterized by XRD, MEB, FT-IR, UV-V absorption, PL, and PLE. The prepared micro powders exhibited a single-phase orthorhombic structure with Pbnm space group. The MEB images revealed grain size ranging from 5 to 20 μm. The CaTiO3 band gap energy decreases by introducing the doping elements and changes from 3.581 eV for the undoped to 2.847 eV for Eu/Dy/Gd/Li doped sample. The photoluminescence properties of Eu3+, Eu3+/Dy3+, and Eu3+/Dy3+/xGd3+ doped CaTiO3 phosphors were investigated through excitation and emission spectra. Under 365 nm excitation, Eu3+/Dy3+ co-doped samples exhibit blue emission, which is turned to near white region by introducing Gd3+ ions. In order to enhance the luminescence properties, (Li+, Mg2+, Sr2+) ions are doped into CaTiO3 Eu3+/Dy3+/Gd3+ phosphors to ensure the host charge compensation. The charge compensators not only provide luminescence enhancement but also modify the local environment of the lanthanide ions and then adjust the emission to tune the ratio of each color in the spectrum. The photometric parameters such as CIE-coordinate and correlated color temperature (CCT) were calculated, which depend on the ion charge and on the ionic radii. These perovskite phosphors can be applied for solid-state lighting applications.

Enhanced photoluminescence in a Eu3+ doped CaTiO3 perovskite phosphor via incorporation of alkali ions for white LEDs

Intense red photoluminescence has been observed in Eu3+/Z+ (Z+ = Li+, Na+ & K+) co-doped CaTiO3 perovskite phosphor materials, synthesized through high temperature solid-state reaction technique. The phosphor materials are structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. All the compounds are crystalline with the orthorhombic phase. The crystallite and particle size of phosphor increase via incorporation of alkali ions. The vibrational groups in phosphor materials are studied by Fourier transform infrared (FTIR) technique. The diffuse reflectance spectra showed a number of peaks in the UV–visible regions due to different transitions of Eu3+ ion. The band gap (Eg) of the phosphor decreases on incorporation of alkali ions. The phosphor materials emit intense red color at 613 nm due to 5D0 → 7F2 transition of Eu3+ ion upon 398 nm and 466 nm excitation wavelengths. The intensity of red emission increases upto 12 mol% concentration of Eu3+ ions. On incorporation of alkali ions in the 12 mol% Eu3+: CaTiO3 phosphor, the emission intensity increases further due to crystallinity, charge compensation and the asymmetry created around the Eu3+ ions in the phosphor. The emission intensity is largest for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The asymmetric ratio is higher for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The lifetime of 5D0 level is enhanced via incorporation of alkali ions and it is also larger for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The CIE color coordinates, correlated color temperature (CCT), color purity and color rendering index (CRI) calculations of the phosphors have also been carried out, which show pure red color in warm light region. Therefore, these synthesized perovskite phosphor materials can be advantageous for display devices, NUV excited red phosphors for making the tricolor phosphor converted WLEDs and blue LED chip-based WLEDs for solid state lighting applications.

Thermoluminescence study and evaluation of trapping parameters CaTiO3: RE (RE=Eu3+, Dy3+) phosphor for TLD applications

Thermoluminescence study of RE3+ (RE3+= Eu3+ and Dy3+) activated CaTiO3 phosphors and determination of trapping parameters are the main focus of this work. Here, CaTiO3: X mol % RE3+ phosphors were synthesized by low temperature solution combustion method at 500 ± 20 OC using citric acid as a fuel. Structure, bonding between each element of the sample and morphology of the sample were analyzed using X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM), which showed that the samples were crystallized in a well known structure. Both the samples were irradiated with 60Co- γ (gamma) source and thermoluminescence studies of both samples were done by Nucleonix TL 1009I thermoluminescence (TL) reader. Chen's peak shape method, Initial rise method and Ilich method are used to determine trapping parameters of both samples like activation energy (E), order of kinetics (b) and frequency factor (s). This all results indicate that both the phosphors are potential candidate for the thermoluminescence dosimetry.

The effect of Mg2+ concentration on structural and luminescent properties of CaTiO3: Eu3+ phosphor

ABSTRACTThe photoluminescence properties of CaTiO3 phosphor powders co-doped with Eu3+ and Mg2+, were prepared by the solid-state reaction method. The powders were characterized by X-ray diffraction, Raman scattering, and photoluminescence spectroscopy. The Crystalline phase and vibrational modes of the phosphors were studied using XRD pattern and Raman Spectrum respectively. The morphological features of the phosphors were characterized by SEM analysis. From Photoluminescence spectra, we have observed two prominent red emission peaks around at 595 nm (5D0 →7F1), 619 nm (5D0 →7F2) with the excitation of 399 nm for Mg2+ codoped CaTiO3:Eu3+ phosphors. The partial substitution of Mg2+ from 0.1 mol% to 0.4 mol% significantly enhanced the luminescent intensity of CaTiO3:Eu3+ phosphors. Furthermore, increase in Mg2+ concentration resulted in concentration quenching. The added Mg2+ increased the color purity which turns to be a potential red phosphor in white light emitting diodes (WLEDs).

Photoluminescence Properties of Pr3+-Activated Ca-Based Perovskites Prepared By Amorphous Complex Method Using Aqueous Metal Complex Solutions

Ca-based perovskite phosphors activated by rare-earth ions have attracted considerable attention recently as prospective materials for various optoelectronic applications. Crystal structure of Ca-based perovskites is highly distorted from the ideal cubic perovskites as SrTiO3. Thus, strong ff-emissions of rare-earth ions should be derived from low site-symmetry of Ca site. In addition, photoluminescence properties of these phosphors are dependent on not only crystal structure of the host materials, but also preparation condition of the samples. Conventional solid-state reaction (SSR) method is not fit for the synthesis of phosphors with complicated compositions because the degree of cation mixing is relatively low due to slow interdiffusion of the cations. In this study, we investigated the preparation of Pr3+-activated Ca-based perovskite phosphors via an aqueous-solution process using metal complex solutions in order to improve the photoluminescence properties of these phosphors. Pr3+-activated CaTiO3 and CaSnO3 phosphors were prepared by amorphous metal complex (AMC) method using stable water-soluble Ti4+ and Sn4+ complexes coordinated to lactic acid. Especially, we developed a new stable water-soluble Sn4+ complex synthesized from SnCl4·nH2O. Photoluminescence properties of Pr3+-activated CaTiO3 and CaSnO3 under UV irradiation were significantly sensitive for the small deviation of the cation ratios of Ti/Ca and Sn/Ca. When the cation ratios in both the phosphors were less than 1.00, ff-emissions from the phosphors prepared by AMC method were low, compared with the phosphors prepared by SSR method. In contrast, when the cation ratios were precisely controlled from 1.00 to 1.05, ff-emissions of the phosphors prepared by AMC method were higher than those prepared by SSR method. Especially, Pr3+-activated CaSnO3 prepared by AMC method at the optimum condition showed high emission intensity under UV irradiation that was 1.9 times higher than those by SSR method (Fig .1). This work was partially supported by Grant-in-Aid for Scientific Research (C) (no. 15K06445) from MEXT, Japan. This work was also partially supported by the cooperative research program of the “Network Joint Research Center for Materials and Devices”. Figure 1

Structural and photoluminescence studies of red emitting CaTiO3:Eu3+ perovskite nanophosphors for lighting applications

Herein, the authors present the spectral studies with quantum efficiency of red emitting Eu3+ doped CaTiO3 downconverting phosphor synthesized by chemical co-precipitation method for the demonstration on the development of solid state lighting devices. The photoluminescence properties of Eu3+ doped CaTiO3 phosphors were investigated through changing the concentration of activator (Eu3+). The structural, morphological and optical properties are systematically characterized by the XRD, FTIR, FESEM, PL and UV–Vis spectroscopy. The synthesized phosphor revealed the single phase orthorhombic structure with space group Pbnm. The FESEM studies exhibited the irregular morphology of the obtained phosphor particles having grain size in the range 70–170 nm. Photoluminescence spectra of CaTiO3:Eu3+ nanophosphor revealed an intense red emission peak around wavelength 619 nm in the visible region upon the excitation of near-UV light at wavelength 397 nm due to 5D0 → 7F2 transition in Eu3+. The Judd–Ofelt intensity parameters were calculated and the quantum efficiency of optimized composition (for Ca0.95TiO3:0.05Eu3+) is found to be 17.46 %. The photometric characterization results revealed that the prepared phosphor can be a suitable candidate for application of solid state lighting devices.

Enhancement of white light emission of Dy3+:CaTiO3 phosphor by Li+ co-doping

A series of white-emitting CaTiO3:Dy3+ and CaTiO3:Dy3+, Li+ phosphors for light-emitting diode applications were prepared by conventional solid-state reactions. The phase of the as-prepared powders were measured by X-ray diffraction pattern. The emission and excitation spectra as well as the luminescence decays were investigated. The excited spectra indicated that they have intense excitation at 353 (6H15/2–6P7/2), 366 (6H15/2–4P5/2), 388 (6H15/2–4I13/2) and 450 nm (6H15/2–4I152). Meanwhile, the emission of Dy3+ ions upon 353 nm excitation was observed at 480 nm (blue) due to the 4F9/2–6H15/2 transitions, 573 nm (yellow) due to 4F9/2–6H13/2 transitions and a weak 665 nm (red) due to 4F9/2–6H11/2 emissions, respectively. As a charge compensator, Li+ ions were incorporated into CaTiO3:Dy3+, which enhanced the PL intensities depending on the doping concentration of Li+. Moreover, the chromaticity coordinates of CaTiO3:Dy3+ and CaTiO3:Dy3+, Li+ were very close to the ideal white light coordinates (0.33, 0.33). All the results demonstrated that CaTiO3:Dy3+ and CaTiO3:Dy3+, Li+ might be potential phosphors for NUV-based white light-emitting diodes.

CaTiO3:Eu3+, a potential red long lasting phosphor: Energy migration and characterization of trap level distribution

This paper comprises a promising approach for the development of a red-light emitting CaTiO3:Eu3+ long-lasting phosphor. Eu3+ doped CaTiO3 phosphors were prepared by the solid state reaction method at 1000°C. Red long-afterglow (LAG) originated from the f–f transitions of Eu3+ in the CaTiO3 and lasted for several minutes. Defect trap depth values from 0.62 up to 1.21eV were obtained from thermoluminescence (TL) data. These defects were created due to charge compensation. These traps were responsible for the afterglow emission at room temperature. The decay curves and TL glow curves showed that the density of the traps with suitable depth has been significantly changed with an increase in dopant concentration. The depth and density of the traps can affect the LAG performance. The possible mechanism behind the LAG of Eu3+ in CaTiO3 was explained in detail on the basis of the trap distribution.

Defect correlated fluorescent quenching and electron phonon coupling in the spectral transition of Eu3+ in CaTiO3 for red emission in display application

This paper reports on the defect correlated self-quenching and spectroscopic investigation of calcium titanate (CaTiO3) phosphors. A series of CaTiO3 phosphors doped with trivalent europium (Eu3+) and codoped with potassium (K+) ions were prepared by the solid state reaction method. The X-ray diffraction results revealed that the obtained powder phosphors consisted out of a single-phase orthorhombic structure and it also indicated that the incorporation of the dopants/co-dopants did not affect the crystal structure. The scanning electron microscopy images revealed the irregular morphology of the prepared phosphors consisting out of μm sized diameter particles. The Eu3+ doped phosphors illuminated with ultraviolet light showed the characteristic red luminescence corresponding to the 5D0→7FJ transitions of Eu3+. As a charge compensator, K+ ions were incorporated into the CaTiO3:Eu3+ phosphors, which enhanced the photoluminescence (PL) intensities depending on the doping concentration of K+. The concentration quenching of Eu3+ in this host is discussed in the light of ion-ion interaction, electron phonon coupling, and defect to ion energy transfer. The spectral characteristics and the Eu-O ligand behaviour were determined using the Judd-Ofelt theory from the PL spectra instead of the absorption spectra. The CIE (International Commission on Illumination) parameters were calculated using spectral energy distribution functions and McCamy's empirical formula. Photometric characterization indicated the suitability of K+ compensated the CaTiO3:Eu3+ phosphor for pure red emission in light-emitting diode applications.

Review of the preparation, characterization, and luminescence properties of Pr3+-doped CaTiO3 phosphors

In this paper we review the luminescence properties of Pr3+-doped CaTiO3 phosphors, the different methods of sample preparation, and characterization of the materials by use of different techniques, for example X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermo-gravimetric analysis, and atomic force microscopy. Solid-state, sol–gel (SG), and combustion methods are most often used for preparation. The high calcining temperature of the solid-state method can be reduced by addition of rare earth oxides (lanthanide series) Ln2O3 and Lu2O3. By use of tetra-n-butyl titanates and calcium nitrates as raw material in the modified solid-state method the luminous properties of samples can be optimized at lower sintering temperatures (600 °C) in less time. SG procedures lead to substantial reinforcement of red photoluminescence intensity so can be regarded as the best technique for phosphor preparation.

Thermal stable Eu-doped CaTiO3 phosphors with morphology-control for high-power tricolor white LEDs

Highly dispersed Eu-doped CaTiO3 H-type morphology phosphors were prepared via solvothermal method and the morphology could be modulated by the temperatures and solvents. The phosphors showed a strong red emission corresponding to the 5D0→7F2 (618nm) of Eu3+ under near-ultraviolet excitation (398nm) and had high interior quantum efficiency. The concentration quenching and the effect of solvents used to synthesize the samples on the luminous performance were discussed as well. Furthermore, these phosphors have excellent thermal stability compared with the commercial Y2O2S:Eu3+ phosphors. Therefore, H-type morphology CaTiO3:Eu3+ is a promising red phosphor under near ultraviolet excitation for high-power tricolor white LEDs.

Low-temperature preparation of monodispersed Eu-doped CaTiO3 LED phosphors with controllable morphologies

A novel solvothermal route has been developed to synthesize mondispersed and different mophologies of Eu-doped CaTiO3 phosphors including magic-column spherical, magic-cube spherical and polyhedral shaped, using a mixture of ethylene glycol (EG) and ethylenediamine (EDA). By tuning the solvent ratio, the method exhibited excellent control over the morphology of CaTiO3:Eu3+, and magic-column spherical phosphors have higher luminous intensities than magic-cube spherical and polyhedral shaped phosphors. The synthesized phosphors had higher luminous intensity and better packing properties than those obtained by a solid-state method. The phosphors showed strong red emissions, corresponding to the 5D0 → 7F2 (617.6 nm) transition of Eu3+ under near-ultraviolet excitation (398.4 nm). X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescent (PL) analyses were used to characterize the structure, morphology and luminous performance of CaTiO3:Eu3+ phosphors.

Preparation of CaTiO<sub>3</sub>:Pr Phosphor by Using CaB<sub>2</sub>O<sub>4</sub> as a Flux

Powder of Pr-doped CaTiO3 phosphor was prepared with addition of CaB2O4 to the starting materials. The primary particle size was increased and the photoluminescence intensity was enhanced by the addition when prepared at 1373 K. The remarkable effects were not observed when prepared at 1273 K.