Dopant distribution and influence of sonication temperature on the pure red light emission of mixed oxide phosphor for solid state lighting

Sm3+-doped strontium barium borate phosphor for white light emission: Spectroscopic properties and Judd-Ofelt analysis

This study aims to explore the spectroscopic properties of a Sr_1.0Ba_2.0B₆O₁₂:0.5Sm³⁺ phosphor synthesized using the solid-state reaction method. The morphology and elemental composition of the phosphor were determined using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. Phase changes and crystallite phases in the phosphor were studied using differential-scanning calorimetry and X-ray diffraction, respectively. Raman and Fourier-transform infrared spectra were used to identify the molecular vibrations in the phosphor. The energy bandgap and bonding nature of the phosphor were analyzed using the absorption spectrum. The nephelauxetic ratios determined from the absorption peaks revealed the presence of both ionic and covalent bonding in the phosphor. Judd-Ofelt parameters, along with radiative properties of the phosphor, were evaluated using the peaks in the absorption spectrum. Colorimetric analysis using the photoluminescence spectrum showed that the Sr_1.0Ba_2.0B₆O₁₂:0.5Sm³⁺ phosphor emits a cool-white light. The higher values of the spectroscopic quality factor, stimulated-emission cross-section, quantum efficiency, and the white-light emission of the phosphor suggest that Sr_1.0Ba_2.0B₆O₁₂:0.5Sm³⁺ is useful for display and lighting applications.

Physical and optical studies of Gd2 O2 S:Eu3+ nanophosphors by microwave irradiation and γ-irradiation methods

Gd₂ O₂ S:Eu³⁺ nanophosphors have been successfully synthesized using microwave irradiation and γ-irradiation methods with polyvinyl pyrrolidone as a stabilizer. The physical and luminescence spectra were compared. The morphologies of both Gd₂ O₂ S:Eu³⁺ nanophosphors were in the hexagonal phase and mainly consisted of spherical nanostructures with diameters of ~90 nm and ~50 nm for both microwave irradiation and γ-irradiation methods. Upon 325 nm of ultraviolet (UV) light excitation, strong red emissions (626 nm) were observed for both methods; these emissions corresponded to the ⁵ D₀ →⁷ F₂ transition of Eu³⁺ ions. However, Gd₂ O₂ S:Eu³⁺ nanophosphors following microwave treatment showed better luminescence intensity than Gd₂ O₂ S:Eu³⁺ nanophosphors treated with γ-irradiation. This difference was attributed to the crystallinity phase and surface quenching effects of Gd₂ O₂ S:Eu³⁺ nanophosphors. The reaction mechanisms of Gd₂ O₂ S:Eu³⁺ nanophosphors in both methods are discussed in detail.

SiO2@LaOF:Eu3+ core-shell functional nanomaterials for sensitive visualization of latent fingerprints and WLED applications

For the first time, intense red color composite of SiO₂@LaOF:Eu³⁺ core-shell nanostructures (NS) were fabricated via facile solvothermal method followed by thermal treatment. The obtained core-shell particles display better spherical shape and non-agglomeration with a narrow size distribution. Photoluminescence (PL) emission spectra exhibits intense peaks at ∼593 nm, 611 nm, 650 nm corresponds to ⁵D₀ → ⁷F_J (J = 0, 1 and 2) Eu³⁺ transitions respectively. The spectral intensity parameters and Eu-O ligand behaviors are estimated by means of Judd-Ofelt (J-O) theory. CIE co-ordinates are found to be (x = 0.63, y = 0.36) which is very close to standard NTSC values (x = 0.67, y = 0.33). CCT value is ∼3475 K which is less than 5000 K, as a result this phosphor is suitable for warm light emitting diodes. The optimized core-shell SiO₂ (coat III)@LaOF:Eu³⁺ (5 mol%) was used as a fluorescent labeling marker for the visualization of latent fingerprints on both porous and non-porous surfaces. Obtained fingerprints are highly sensitive and selective also no background hindrance which enables level-I to level-III fingerprint ridge characteristics. Observed results indicate that the significant improvement in luminescence of coreshell NS can be explored as a sensitive functional nanopowder for advanced forensic and solid state lightning applications.

Appearance of efficient luminescence energy transfer in doped orthovanadate nanocrystals

This paper reports the detailed synthesis mechanism and the structural, morphological and optical characterization of ultraviolet (∼311 nm) excitable samarium doped gadolinium yttrium orthovanadate, (Gd,Y)VO4:Sm3+, nanocrystals. X-ray diffraction and Rietveld refinement studies confirmed that the synthesized samples crystallize in a tetragonal structure withI41/amdspace group. The enhanced photoluminescence intensity of (Gd,Y)VO4:Sm3+compared with the existing YVO4:Sm3+phosphor clearly indicates the significant role of Gd3+ions. This has been attributed to the sensitization of the6PJenergy level of Gd3+ions by energy transfer from orthovanadate (VO43−) ions and subsequent energy trapping by Sm3+ions. The energy transfer from VO43−to Sm3+viaGd3+ions as intermediates and concentration quenching of Gd3+luminescence are discussed in detail. The optical band gap of the as-prepared nanocrystals has been estimated using UV–vis–NIR absorption spectroscopy, which reveals a slightly higher band gap (3.75 eV) for YVO4as compared to GdYVO4(3.50 eV). Furthermore, confocal microcopy, decay parameters and Commission Internationale de l'Eclairage chromatic coordinates have supplemented these studies, which established the suitability of these nanophosphors for achieving spectral conversion in silicon solar cells.

Synthesis and Behavior of Cetyltrimethyl Ammonium Bromide Stabilized Zn1+xSnO3+x (0 ≤ x ≤1) Nano-Crystallites

We report synthesis of cetyltrimethyl ammonium bromide (CTAB) stabilized Zn_1+xSnO_3+x (0 ≤ x ≤1) nano-crystallites by facile cost-effective wet chemistry route. The X-ray diffraction patterns of as-synthesized powders at the Zn/Sn ratio of 1 exhibited formation of ZnSn(OH)₆. Increasing the Zn/Sn ratio further resulted in the precipitation of an additional phase corresponding to Zn(OH)₂. The decomposition of these powders at 650°C for 3h led to the formation of the orthorhombic phase of ZnSnO₃ and tetragonal SnO₂-type phase of Zn₂SnO₄ at the Zn/Sn ratio of 1 and 2, respectively, with the formation of their mixed phases at intermediate compositions, i.e., at Zn/Sn ratio of 1.25, 1.50 and 1.75, respectively. The lattice parameters of orthorhombic and tetragonal phases were a ~ 3.6203 Å, b ~ 4.2646 Å and c ~ 12.8291Å (for ZnSnO₃) and a = b ~ 5.0136 Å and c ~ 3.3055Å (for Zn₂SnO₄). The transmission electron micrographs revealed the formation of nano-crystallites with aspect ratio ~ 2; the length and thickness being 24, 13 nm (for ZnSnO₃) and 47, 22 nm (for Zn₂SnO₄), respectively. The estimated direct bandgap values for the ZnSnO₃ and Zn₂SnO₄ were found to be 4.21 eV and 4.12 eV, respectively. The ac conductivity values at room temperature (at 10 kHz) for the ZnSnO₃ and Zn₂SnO₄ samples were 8.02 × 10⁻⁸ Ω^-1 cm^-1 and 6.77 × 10⁻⁸ Ω^-1 cm^-1, respectively. The relative permittivity was found to increase with increase in temperature, the room temperature values being 14.24 and 25.22 for the samples ZnSnO₃ and Zn₂SnO₄, respectively. Both the samples, i.e., ZnSnO₃ and Zn₂SnO₄, exhibited low values of loss tangent up to 300 K, the room temperature values being 0.89 and 0.72, respectively. A dye-sensitized solar cell has been fabricated using the optimized sample of zinc stannate photo-anode, i.e., Zn₂SnO₄. The cyclic voltammetry revealed oxidation and reduction around 0.40 V (current density ~ 11.1 mA/cm²) and 0.57 V (current density– 11.7 mA/cm²) for Zn₂SnO₄ photo-anode in presence of light.

Structural, optical and special spectral changes of Dy3+ emissions in orthovanadates

This paper reports on the structural, optical and photometric characterization of yttrium gadolinium orthovanadates (Y_1−xGd_xVO₄) doped with Dy³⁺ for white emission in solid state lighting.