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.

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 structural, optical and photometric characterization of an Eu3+/Dy3+ doped yttrium oxysulfide phosphor (Y2O2S:Eu3+/Dy3+) for near white emission in solid state lighting. A series of Y2O2S phosphors doped with Eu3+/Dy3+ were prepared by the hydrothermal method. The microstructures of the as-synthesized phosphors were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results reveal that the obtained powder phosphors have a single-phase hexagonal structure and also indicate that the incorporation of the dopants/co-dopants did not affect the crystal structure. The SEM images reveal the morphology of the prepared phosphors as an intense interpenetrating network of interconnected micro-fibers with a diameter of about 0.15 μm. The band gap of the phosphors was calculated from diffuse reflectance spectra using the Kubelka–Munk function. The Eu3+, Dy3+ doped and Eu3+/Dy3+ co-doped phosphors illuminated with ultraviolet light showed characteristic red luminescence corresponding to the 5D0→7FJ transitions of Eu3+ and characteristic blue and yellow luminescence corresponding to the 4F9/2→6H15/2 or 4F9/2→6H13/2 transitions of Dy3+. The luminescence spectra, the energy transfer efficiency and the decay curves of the phosphors indicated that there exists a strong energy transfer from Dy3+ to Eu3+ and this was demonstrated to be a resonant type via a dipole–quadrupole reaction. Furthermore, the critical distance of the Eu3+ and Dy3+ ions have also been calculated. By utilizing the principle of energy transfer it was also demonstrated that with an appropriate tuning of the activator content the Y2O2S:Eu3+/Dy3+ phosphors can exhibit a great potential to act as single-emitting component phosphors for white light emission in solid state lighting technology.

The energy transfer phenomena and colour tunability in Y2O2S:Eu3+/Dy3+ micro-fibers for white emission in solid state lighting applications

Tm(3+), Dy(3+), and Eu(3+) codoped NaGd(WO4)2 phosphors were prepared by a facile hydrothermal process; they were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectrometer (EDS), photoluminescence spectra, and fluorescence lifetime. The results show that the novel octahedral microcrystals with a mean side length of 2 μm are obtained. Under the excitation of ultraviolet, individual RE(3+) ion (Tm(3+), Dy(3+), and Eu(3+)) activated NaGd(WO4)2 phosphors exhibit excellent emission properties in their respective regions. Moreover, when codoping Dy(3+) and Eu(3+)/Tm(3+) in the single component, the energy migration from Dy(3+) to Eu(3+) has been demonstrated to be a resonant type via a dipole-quadrupole mechanism as well as that from Tm(3+) to Dy(3+) ions, of which the critical distance (R(Dy-Eu)) is calculated to be 11.08 A. More significantly, in the Tm(3+), Dy(3+), and Eu(3+) tridoped NaGd(WO4)2 phosphors, the energy migration of Tm(3+)-Dy(3+)-Eu(3+), utilized for sensitizing Eu(3+) ions besides compensating the red component at low Eu(3+) doping concentration, has been discussed first. In addition, under 365 nm near-ultraviolet radiation (nUV), the color-tunable emissions in octahedral NaGd(WO4)2 microcrystals are realized by giving abundant blue, green, white, yellow, and red emissions, especially warm white emission, and could be favorable candidates in full-color phosphors for nUV-LEDs.

Single-component and warm-white-emitting phosphor NaGd(WO4)2:Tm3+, Dy3+, Eu3+: synthesis, luminescence, energy transfer, and tunable color.

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Rare-Earth Doping in Nanostructured Inorganic Materials.

The cation substitution-dependent phase transition was used as a strategy to discover new solid solution phosphors and to efficiently tune the luminescence property of divalent europium (Eu2+) in the M3(PO4)2:Eu2+ (M = Ca/Sr/Ba) quasi-binary sets. Several new phosphors including the greenish-white SrCa2(PO4)2:Eu2+, the yellow Sr2Ca(PO4)2:Eu2+, and the cyan Ba2Ca(PO4)2:Eu2+ were reported, and the drastic red shift of the emission toward the phase transition point was discussed. Different behavior of luminescence evolution in response to structural variation was verified among the three M3(PO4)2:Eu2+ joins. Sr3(PO4)2 and Ba3(PO4)2 form a continuous isostructural solid solution set in which Eu2+ exhibits a similar symmetric narrow-band blue emission centered at 416 nm, whereas Sr2+ substituting Ca2+ in Ca3(PO4)2 induces a composition-dependent phase transition and the peaking emission gets red shifted to 527 nm approaching the phase transition point. In the Ca3–xBax(PO4)2:Eu2+ set, the validity of crystalloc...

Discovery of New Solid Solution Phosphors via Cation Substitution-Dependent Phase Transition in M3(PO4)2:Eu2+ (M = Ca/Sr/Ba) Quasi-Binary Sets

A series of CaMoO4 phosphors doped with trivalent dysprosium (Dy3+) and codoped with potassium (K+) ions were prepared by hydrothermal method. The nanostructures of the as-synthesized phosphors were investigated by X-ray diffraction (XRD). The results reveal that the obtained powder phosphors are single-phase scheelite structure with tetragonal symmetry and the crystallite size is in the range of 10–60 nm. The emission spectra show a bright yellow emission at 576 nm and blue emission at 487 nm. As a charge compensator, K+ ions were incorporated into CaMoO4:Dy3+ phosphors, which enhance the PL intensities depending on the doping concentration of K+. The CIE parameters such as colour coordinates, colour correlated temperature and luminous efficacy of radiation were calculated using spectral energy distribution functions and McCamy's empirical formula. Photometric characterization indicates the suitability of K+ compensated CaMoO4:Dy3+ phosphor for white LED applications.

Luminescence and photometric characterization of K+ compensated CaMoO4:Dy3+ nanophosphors

In the present paper, a comparative investigation on the structural and photoluminescence properties of Y2O3:Eu3+ phosphor prepared by different wet chemical synthesis routes such as sol-lyophilisation (SL), combustion (CR), hydrothermal (HT) and microwave assisted hydrothermal combustion (MHWC), has been reported for the first time. The MHWC derived phosphor exhibited better photoluminescence than that of the samples obtained with other adopted methods. Such outcomes were due to the increased crystallinity, well defined morphology and improved compositional homogeneity in the MWHC technique. The growth of the prepared phosphors was explained in the light of chemical kinetics. Jorgensen formula and nephelauxetic ratio was used to understand the ligand behavior of Eu–O bond and to estimate the electron phonon coupling in Y2O3:Eu3+ phosphor. The spectroscopic behavior of Y2O3:Eu3+ phosphor, prepared by different routes, was determined using Judd–Ofelt theory. Thermal stability, purity and efficiency of the emitted colour were checked on the basis of different synthetic approach. An efficient synthesis method for Y2O3:Eu3+ phosphor, compatible for industrial appliances, was proposed.

Synthesis of strong red emitting Y2O3:Eu3+ phosphor by potential chemical routes: comparative investigations on the structural evolutions, photometric properties and Judd–Ofelt analysis

A series of Dy3+/K+ doped calcium molybdate phosphors were synthesized by a hydrothermal synthesis method and structural, photoluminescence and decay studies were carried out. The crystal structure and phase of the prepared phosphors were investigated using X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). These studies show that the phosphors are of a tetragonal structure with a nanorod morphology. The photoluminescence results indicate that these phosphors could be efficiently excited by near-ultraviolet radiation which causes emission in the blue and yellow regions. A novel approach was used to calculate different spectral parameters of powder samples using excitation spectra instead of conventional absorption spectra. Quantitative calculation of spectral parameters, luminescence decay and quantum yield suggest the suitability of this phosphor as an efficient luminescent medium for light emitting devices.

Excitation spectra and luminescence decay analysis of K+ compensated Dy3+ doped CaMoO4 phosphors

This paper reports a spectroscopic investigation of Eu3+ doped SnO2 nanoparticles. A series of Eu3+ doped SnO2 nanoparticles were prepared by the simple and efficient combustion method. The X-ray diffraction results reveal that the obtained powder nanoparticles consist of a single phase tetragonal structure. The FESEM images reveal an irregular agglomerated morphology indicating an increase in particle size with increase in Eu3+ concentration. The Eu3+ doped nanoparticles illuminated with UV light show the characteristic red luminescence corresponding to the 5D0 → 7FJ transitions of Eu3+. The concentration quenching phenomenon is discussed in the light of energy transfer, electron–phonon coupling and ion–ion interaction. The spectral characteristics and Eu–O ligand behavior were discussed in the light of Judd–Ofelt parameters using the PL emission spectra instead of the conventional absorption spectra. The CIE parameters were calculated using the spectral energy distribution function and McCamy's empirical formula. Photometric characterization indicates the suitability of Eu3+ doped SnO2 nanoparticles for red emission in light-emitting diodes.

S. K. Sharma

Papers

Luminescence and photometric characterization of K+ compensated CaMoO4:Dy3+ nanophosphors

The energy transfer phenomena and colour tunability in Y2O2S:Eu3+/Dy3+ micro-fibers for white emission in solid state lighting applications

Synthesis of strong red emitting Y2O3:Eu3+ phosphor by potential chemical routes: comparative investigations on the structural evolutions, photometric properties and Judd–Ofelt analysis

Excitation spectra and luminescence decay analysis of K+ compensated Dy3+ doped CaMoO4 phosphors

Spectroscopic behavior of Eu3+ in SnO2 for tunable red emission in solid state lighting devices