Papers by Keyword: Energy Transfer

Abstract: With a high melting point (>2400°C), superior thermal conductivity, and a large band gap (5.8 eV), Y₂O₃ exhibits a high dielectric constant (14–18), a refractive index of ~1.9, and excellent chemical resistance. Its low phonon vibration frequency (~380 cm⁻¹) enables efficient energy transitions for rare-earth (RE) ions, enhancing its suitability as a host for luminescent phosphors. In this study, Y₂O₃ nanoparticles doped with Eu³⁺ and sensitized with either Li⁺ or Bi³⁺ were synthesized via polyol method. A comparative investigation was conducted to evaluate the energy transfer efficiency and luminescence enhancement provided by each sensitizer. Structural and morphological characteristics were examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM), while Fourier-transform infrared spectroscopy (FT-IR) was employed to study absorption features. Photoluminescence (PL) analysis revealed the impact of sensitizer ions on emission intensity, identifying the most effective combination for optimized luminescent performance. These findings demonstrate the potential of sensitized Y₂O₃:Eu³⁺ nanoparticles for advanced luminescence-based applications.

Abstract: Frequency upconversion (UC) photoluminescence (PL) in PbO-B₂O₃ glass codoped with trivalent ions of neodymium (Nd³⁺) and ytterbium (Yb³⁺) is prepared by melt quench method. X-ray diffraction (XRD) and differential scanning carorimetry (DSC) done for structural and thermal studies. Physical properties as density, oxygen packing density, lanthanide ion concentration etc. calculated. Photoluminescence of the sample gives the information of spectral lines, corresponding to the Nd3+ transitions ⁴G_9/2 ⁴I_9/2 (at 500 nm), ⁴G_7/2 ⁴I_9/2 (at 550 nm), [⁴G_5/2; ²G_7/2] ⁴I_11/2 (at 595 nm) and ⁴G_7/2 ⁴I_13/2 (at 660 nm). The dependence of the UC intensity with the Yb³⁺ concentration and the time behavior of the UC signal indicated the presence of two energy transfer (ET) pathways involving Nd³⁺-Yb³⁺ pairs and Yb³⁺-Nd³⁺-Yb³⁺ triads. Rate-equations for the population densities of the lanthanide energy levels were used to describe the dynamics of the UC emission and to determine the ET rates.

Abstract: Self-activated multicolor phosphors are being used in more and more emerging fields. In order to explore the energy transfer between [NbO₆]^7- coordination groups and Sm³⁺ ions, a series of Ba_3-ySm_yTa_1-xNb_xGa₃Si₂O₁₄ samples co-doped with Nb⁵⁺ and Sm³⁺ were prepared in this work, and the changes of luminous intensity under the condition of fixed Nb⁵⁺ concentration regulating Sm³⁺ concentration and fixed Sm³⁺ concentration regulating Nb⁵⁺ concentration were obtained respectively. By further fitting the emission decay curves of Sm³⁺ under two conditions, the decreasing average lifetime is obtained. Thermal stability tests of the samples also hinted the presence of such energy transfer. This regular change can provide a good reference for developing new self-activated phosphors.

Abstract: Green light-emitting YPO₄:Tb³⁺ and YPO₄:Tb³⁺: Ce³⁺ nanoparticles were synthesised at low temperatures using the polyol method. The phase purity, micromorphology and luminescence characteristics were studied using Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier Transfer Infrared absorption spectroscopy (FT-IR) and Photoluminescence spectroscopy (PL). Combined XRD and TEM analysis showed that the YPO₄ nanoparticles crystallised into a single phase of tetragonal (I41/amd) structure. For all samples, the emission intensity at λ_em=543 nm assigned to ⁵D₄→⁷F₅ is more prominent than ⁵D₄→⁷F₆ with a maximum at λ_em=488 nm, and the asymmetric ratio was calculated and analysed. The asymmetric ratio is strongly correlated with the symmetry around the local environment of Tb³⁺ ions. A significant increase in the asymmetric ratio is observed with an increase in annealing temperature. The energy transfer from Ce³⁺ ions to Tb³⁺ ions was tested by studying the photoluminescence properties of YPO₄:Tb³⁺ and YPO₄:Tb³⁺: Ce³⁺ nanoparticles and how it results in the improvement of the luminescence intensity. The Ce³⁺ 5d−4f and Tb^{3+ 5}D₄→⁷F_J (J = 6 − 3) transitions were observed.

Abstract: Red light emitting YPO₄: Eu³⁺ and YPO₄: Tb³⁺: Li⁺ nanoparticles were synthesised using polyol method at low temperatures. The phase purity, micromorphology, and luminescence characteristics were studied using Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier Transfer Infrared absorption spectroscopy (FT-IR). Combined XRD and TEM analysis showed that the YPO₄ nanoparticles crystallized into a single phase of tetragonal (I41/amd) structure. The energy transfer from Li⁺ ions to Eu³⁺ ions was tested by studying the photoluminescence properties of YPO₄: Eu³⁺and YPO₄: Eu³⁺: Li⁺ nanoparticles and how it results in the improvement of the luminescence intensity.

Abstract: The Er³⁺/Nd³⁺ doped glasses of the form (69-x)TeO₂-15Li₂CO₃-15Nb₂O₅-1Er₂O₃-(x)Nd₂O₃ with x=0.4, 0.8 and 1.0 mol % are successfully made by using conventional melt-quenching technique. It was found both the photoluminescence intensity and stimulated emission cross-section were found increase with Nd³⁺ codoping. Efficient blue (497 nm, ²G_9/2 → ⁴I_9/2), green (550 nm, ²G_7/2 → ⁴I_9/2), orange (618 nm, ²H_11/2→⁴I_9/2), and red (635 nm, ⁴F_9/2→⁴I_9/2) spectra were observed. The results suggest that the present glass shows the potential candidate of broadband amplifiers and lasers as it is comparable with other Nd³⁺ doped other host.

Abstract: A new tungstate family, Li₃Ba₂Gd₃(WO₄)₈ doped with Tb³⁺ is synthesized by using a conventional high-temperature solid-state method to explore new pure green phosphors for white light-emitting diodes (WLEDs). The results from the X-Ray patterns show that the crystal structures of the hosts are composed of tungstate zigzags and the Gd³⁺-Gd³⁺ units, which are isolated by the [WO₄]^2- groups. The critical concentration of Tb³⁺ is up to x=2.0 in the singly doped phosphors, which is ascribed to the interaction of the isolated Gd³⁺ ions being mitigated by [WO₄]^2- groups. The characteristic green emission peaks at around 547 nm are also observed, which result from the ⁵D₄→⁷F₅ transition of Tb³⁺ ions, and the optimal doping concentration is x=2.0.

Abstract: This study is a kinematic model of a mechanical mill that works with a single ball in motion, and which is operated by a crank and connecting rod system for producing nanocrystalline powders by the process of ball milling. The geometric and dynamic parameters play an important role on the variation of forces created upon impact of the ball with the inside wall of the vial, which caused energy transfer required for the mechanical alloying process. The determination of these forces enables us to know their specific magnitudes on the intensity and milling efficiency, with the advantage of low operating power consumption of the mill and absence of the contamination problem. In addition, we have defined a model for calculating the temperature of the powder trapped between the ball and the wall of the vial of the mechanical mill whose start-up is provided by an electric motor.

Abstract: The (Gd_0.9-xTb_0.1Dy_x)₃Al₅O₁₂ (x=0-0.04, GdAG:Tb³⁺/Dy³⁺) solid solution was acquired by calcining their respective precursor prepared via co-precipitation method at 1500 °C. The performance of GdAG:Tb³⁺/Dy³⁺ powders was characterized by combined technology of Fourier transform infrared absorption spectra (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and photoluminescence (PL) spectrum analyses. The metastable Gd₃Al₅O₁₂ could be stabilized by doping smaller Tb³⁺ ions of 10 at.%. Under the optimal UV excitation of 275 nm, the GdAG:Tb³⁺/Dy³⁺ phosphors exhibit vivid green emission at 548 nm which were attributed to the ⁵D₄→⁷F₅ transition of Tb³⁺. The CIE chromaticity coordinate was determined at (~0.32, ~0.48) with the color temperature of ~5872 K. Compared to the Dy³⁺-free (Gd_0.9Tb_0.1)AG phosphor, the emission intensity of Dy³⁺-doped phosphors display stronger owing to the efficient energy transfer from Dy³⁺ to Tb³⁺. The optimal amount of Dy³⁺ in GdAG:Tb³⁺/Dy³⁺ phosphors was determined to be ~2.5 at.% (x=0.025). The GdAG:Tb³⁺/Dy³⁺ phosphors developed in present work are expected to be a new type of green phosphor widely used in the lighting and display areas.

Abstract: The results of the study of spectral and decay kinetic characteristics of the pulse cathodoluminescence (PCL) for the group of industrial “white” LEDs phosphors with different composition of the host and dopants are presented. The quantitative characteristics of the PCL: position and half-width of the luminescence spectra, the luminescence decay times were determined.