Papers by Keyword: Luminescence

Abstract: Well-grown Ba₉Sc₂Si₆O₂₄:Ce³⁺ phosphors were synthesized by a novel melt quenching synthesis method. Sintered phosphor balls with excellent luminescent characteristics were obtained. This method is useful tool for rapid screening of phosphor materials.

Abstract: Sc_0.88Lu_0.05(V_1-xP_x)O₄:Eu³⁺_0.07(0≤x≤0.5) phosphors were synthesized by co-precipitation method. The structure, morphology and luminescence spectra of samples were investigated by XRD, SEM and fluorescence spectrophotometer, respectively. The samples doped with Eu³⁺, Lu³⁺ and PO₄^3- can maintain the body-centered tetragonal structure of ScVO₄ and the morphology essentially remains unchanged with slight agglomeration. The excitation spectrum intensity of Sc_0.88Lu_0.05(V_1-xP_x)O₄:Eu³⁺_0.07 increase within the near UV excitation (360-410nm). The optimum doping concentration of PO₄^3- is 0.2(x value), and the maximum emission intensity of Sc_0.88Lu_0.05(V_0.8P_0.2)O₄:Eu³⁺_0.07 is about 35 % higher than the Sc_0.88Lu_0.05VO₄:Eu³⁺_0.07 under 365 nm excitation. Decay curve of ⁵D₀ state for as-prepared samples fits the single order exponential behavior, the lifetime of ⁵D₀ increase first and then decrease with the increase of PO₄^3- doping concentration. The internal quantum efficiency is up to 66.73% under 365nm excitation, When the temperature rises to 200°C, the emission intensity maintains 79.3% of that in the room temperature. Sc_0.88Lu_0.05(V_0.8P_0.2)O₄:Eu³⁺_0.07 phosphor shows high internal quantum efficiency and thermal stability, which is suitable for the UV-pumped white LED as red phosphor.

Abstract: A series of novel luminescent materials Ca₁₀M(PO₄)₇:Eu²⁺ (M: Li, Na, K) were synthesized by the solid-state reaction. The previous literatures indicate that the doped different alkali metal ions can only lead to regular shift of the emission and excitation spectra. Howerver, in this paper, we found the result that these three kinds of phosphors showed huge differences between the emission spectra intensity as well as the positions of the excitation and emission spectra peaks. No any regulars can be found. In order to explore it, crystal structure, the performance of photoluminescence spectra and CIE coordinates have been systematically investigated and discussed. In Ca₁₀Li (PO₄)₇, Ca₁₀Na (PO₄)₇ and Ca₁₀K(PO₄)₇ host lattices, the positions of the cations are different, leading to three different crystal structures. Besides, the coordination conditions of the luminescent centers Eu²⁺ ions are also changed by the incorporation of the alkali metal ions. Thus the enormous disparity on the luminescence intensity as well as the excitation and emission peak positions may be ascribed to these three quite different crystal fields and different coordination numbers of the luminescent central ion in the Ca₁₀M(PO₄)₇:Eu²⁺ (M: Li, Na, K) phosphors.

Abstract: A series of europium doped magnesium borotellurite glasses embedded with manganese nanoparticles (Mn₃O₄ NPs) of composition (59-x)TeO₂-30B₂O₃-10MgO-x1Eu₂O₃-1Mn₃O₄ with 0.5 ≤ x ≤ 1.5 mol % are prepared using melt quenching technique. The existence of broad hump in X-ray diffraction (XRD) pattern verifies the amorphous nature of glasses. The presence of Mn₃O₄ NPs with average diameter of ~11 nm and (1 0 3) lattice plane having 0.276 nm spacing in the glass matrix is confirmed by high resolution transmission electron microscope (HRTEM) image. The glass samples are excited under 390 nm excitation wavelength and the emission spectra are found to consist of four emission peaks centred at 587 nm, 610 nm, 651 nm and 700 nm assigned to the transition from ⁵D₀ →⁷F_J (J = 1, 2, 3, 4) states. The schematic energy level diagram is proposed. All results will be discussed with respect to the composition of Eu³⁺ ion.

Abstract: Borate glass system of composition (100-x)B₂O₃-15Al₂O₃-20CaO-0.4Fe₂O₃-xCeO₂ with x = 0, 0.25, 0.50, 0.75, and 1.0 mol% were prepared using conventional melt-quenching method. Optical measurements were carried out at room temperature to determine the Cerium (Ce³⁺) ions concentration dependent absorption and luminescence emission properties of such glass system. Optical energy band gap of the glass system were evaluated as a function of Ce³⁺ ions content. Indirect band gap energy was found to be lower than the direct band gap energy. Urbach energy was ranged between 0.12-0.17 eV. An increased broad absorption is observed in the UV region with increasing Ce³⁺ ions concentration. The emission spectra of the glass system recorded with 380 nm excitation wavelength revealed prominent cyan-green emission.

Abstract: Weak stimulated emission cross-section of rare earth ions (REIs) as dopants inside various glass hosts are disadvantageous for practical applications and needs improvement. We determine the mechanism of Titania (TiO₂) nanoparticles (TNPs) mediated Surface Plasmon Resonance (SPR) assisted modification in the spectral properties of tellurite glass doped with Erbium (Er³⁺) ions. Transparent and thermally stable glass samples with varying TNPs contents are synthesized using melt-quenching technique. TEM images revealed the existence of TNPs with average size ranged from 16 to 26 nm. Glass containing 0.4 mol% of TNPs displayed an enhancement in the Raman signal by a factor of 2.25, 1.83, 1.98, 1.56 and 3.58 for the bands centered at 388, 495, 673, 758, and 845 cm^-1, which is attributed to the SPR assisted effects. Absorption spectra of TNPs embedded glass (devoid of erbium ions) manifested two surface plasmon (SP) bands at 552 and 580 nm. Up-conversion (UC) PL spectra showed three prominent bands centered at 525, 545, and 660 nm due to the Er³⁺ ion transition from the excited states to the ground state. Furthermore, glass containing 0.4 mol% of TiNPs exhibited an intensity enhancement by a factor of 30, and 28.57 (green bands) and 19.60 (red band), which are ascribed to the generation of strong local electric field mediated by SPR effect of TNPs situated in the vicinity of Er³⁺ ion. The presence of TNPs surface plasmon is asserted to be responsible for the alteration of the Er³⁺ ions absorbance and modification of the UC emission intensity. A correlation between SPR and Surface Enhance Raman Scattering (SERS) is established.

Abstract: The modification of absorption characteristics in rare-earth doped tellurite glasses is important in photonics application. The Er³⁺/Nd³⁺ doped glasses of the form (69-x)TeO₂–15Li₂CO₃–15Nb₂O₅–1Er₂O₃ -(x)Nd₂O₃ with x =0.2 and 0.6 mol% are successfully made by using conventional melt-quenching technique. The Judd-Ofelt analysis is to determine the local structure and bonding in the vicinity of rare-earth ions. The oscillator strengths are calculated from the absorption spectra and used to evaluate Judd-Ofelt intensity parameters (Ω_λ, λ=2, 4 and 6). The values of Ω₄ and Ω₆ change with the increase of Nd³⁺ concentration is ascribed to the change in glass network structures. The values of Ω₂ are increased from 1.53 to 37.13 (10^-22) cm² with the increase of Nd³⁺ concentration which indicate an increase in the covalent nature of Nd-O bond and less centrosymmetrical the ion sites. The decrease in τ_rad for each level with the increase of Nd³⁺ concentration signifies on how fast a particular level gets depopulated. The values of β for the transitions ⁴G_5/2, ²G_7/2 → ⁴I_9/2, ²H_11/2 → ⁴I_9/2 and ⁴F_9/2 → ⁴I_9/2 are found to lie in between 99.6 to 100.0%.

Abstract: The optical behaviour of Er³⁺ (1.0 – 2.0 mol %) doped B₂O₃-TeO₂- Na₂O-MgO glasses synthesized by conventional melt-quenching technique was studied through luminescence measurements. The X-ray diffraction (XRD) pattern confirms the amorphous nature of the glasses without the existence of any sharp peak. The emission spectra at 378 nm excitation displayed three emission peaks corresponding to ²H_11/2-⁴I_15/2, ⁴S_3/2-⁴I_15/2 and ⁴I_9/2-⁴I_15/2 transitions. Hence, a schematic energy level diagram was proposed. The luminescence properties of the prepared glasses was found to be strongly affected by varying the concentration of Er³⁺ ions.

Abstract: Annealing time dependent optical properties of melt-quench synthesized Er³⁺-doped (0.5 mol%) zinc-boro-tellurite (ZBT) glasses containing silver (Ag) nanoparticles (NPs) (1.0 mol%) are reported. Heat treatment (HT) durations are varied to control NPs growth. Reduction of NPs sizes from 12.7 to 6.6 nm for HT time beyond 6 hr at 410 °C is ascribed to their diffusion limited growth. Surface plasmon resonance bands evidenced at 550 and 580 nm are red shifted. Luminescence intensity enhancement is majorly attributed to the local field effect of Ag NPs and quenching is due to the energy transfer from NPs to Er³⁺. Present glass compositions are promising for the development of photonic devices.

Abstract: The white light generation mechanism was explained depending on mixing colors from the illuminated CdTe/ZnSe core/shell nanocrystals. The color mixed in CdTe/ZnSe core/shell system were used to generate intense white light when illuminated by InGaN/GaN UV LED (λ=360 nm) the core/shell system tuned the chromaticity coordinates to (0.30, 0.32) and increased the intensity of the emitted white light. This improvement was attributed to the overlap of emission with the photoluminescence (PL) spectrum of CdTe/ZnSe core/shell which leads to a cold white light generation.