Browsing by Subject "PEROVSKITE"
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Item Phase transition and luminescence characteristics of dysprosium doped strontium stannate phosphor synthesized using hydrothermal method(ELSEVIER SCI LTD) Kaynar, H; Coban, MB; Madkhli, AY; Ayvacikli, M; Can, NA series of strontium stannate (SrSnO3) doped with Dy3+ ions at various wt % concentrations (1, 2, 3 and 5) were synthesized via hydrothermal reaction and analysed using X-ray diffraction (XRD), energy dispersive spectros-copy (EDS), environmental electron scanning microscope (ESEM), photoluminescence (PL) and, cath-odoluminescence (CL). The XRD results confirmed that all samples were assigned to cubic perovskite-type SrSnO3 structured with the Pm3m space group. The PL emission spectrum of Dy3+ activated samples consisted of some characteristic peaks located at 481 nm, 572 nm, 660 nm and 753 nm, corresponding to (4F9/2 -> 6H15/2, blue), (4F9/2 -> 6H13/2, yellow), 660 nm (4F9/2 -> 6H11/2, red) and 753 nm (4F9/2 -> 6H9/2, red) transitions. The PL emission line intensity is gradually enhanced with an increase in doping concentration up to 3 wt %, followed by concentration quenching. The confinement effects of localized resonant energy transfer might cause higher concentration quenching. PL emission spectra were affected by the temperature range from 10 K to 300 K. PL emission anomalies at 270 K in SrSnO3:Dy3+ have been reported to be consistent with a structural phase tran-sition at this temperature. This work confirms Singh et al.'s observation, revealing that SrSnO3 has a phase transition at 270 K.Item Ultra-stable Eu3+/Dy3+co-doped CsPbBr3 quantum dot glass nanocomposites with tunable luminescence properties for phosphor-free WLED applications(ELSEVIER SCIENCE SA) Erol, E; Vahedigharehchopogh, N; Ekim, U; Uza, N; Ersundu, MÇ; Ersundu, AEColloidal CsPbBr3 perovskite quantum dots (PQDs) have substantially improved modern optoelectronic applications, including solid-state lighting, thanks to their highly pure and intense green light emission. However, some drawbacks including lead toxicity, poor stability, and difficulties in emission color tuning hinder their practical applications. Herein, ultra-stable Eu3+/Dy3+ co-doped CsPbBr(3 )PQD glass nano-composites (GNCs) with tunable color emissions from green to red and then white are synthesized via melt-quenching followed by heat-treatment method to be used in white light-emitting diodes (WLEDs). Eu3+ and Dy3+ ions are selected to overcome the color tunability obstacle of PQDs and to obtain phosphor-free white light emission with enhanced CRI values. The photoluminescent performance of GNCs is shown to be reversible at elevated temperatures and remains stable even in water. Ultimately, a prototype WLED is constructed by coupling a selected Eu3+/Dy3+ co-doped CsPbBr3 PQD GNC on top of a 400 nm-emitting LED chip to demonstrate its superior optical performance with a color rendering index of 78 and correlated color temperature of 5436 K. The developed GNCs with long-term stability, and excellent tunable luminescent properties may overcome the commercialization barriers of CsPbBr3 PQDs for WLED applications. (C) 2022 Elsevier B.V. All rights reserved.Item Synthesis and Luminescence Properties of Trivalent Rare-Earth Element-Doped Calcium Stannate Phosphors(TAYLOR & FRANCIS INC) Karabulut, Y; Ayvacikli, M; Canimoglu, A; Guinea, JG; Kotan, Z; Ekdal, E; Akyuz, O; Can, NThe phosphors of calcium stannate activated with individual trivalent rare-earth element (REE) ions (Neodymium III, Europium III, Terbium III, Dysprosium III, and Samarium III) were synthesized by high-temperature solid-state reaction (SSR), and their characterization and luminescent properties were investigated. The crystal structures and morphologies of the resultant materials were well characterized by experimental techniques such as X-ray powder diffraction (XRD) and environmental scanning electron microscopy (ESEM). The XRD results display that the rare-earths substitution of Calcium II does not change the structure of calcium stannate host. Obviously, the ESEM image exhibits that phosphors aggregate and their particles with irregular shape exist. The calcined powders of the Europium III, Neodymium III, Samarium III, Dysprosium III, and Terbium III ions doped in calcium stannate exhibits bright red, reddish orange, yellowish, orange white, and green light, respectively. Although there is some intrinsic emission ranging from UV to near-infrared (NIR) due to the host lattice, the dominant signals are from the rare-earth sites, with signals characteristic of the trivalent rare-earth states. The emission spectrum from undoped-calcium stannate phosphor is characterized by two broad bands centered at similar to 800 and similar to 950nm. The shapes of the emission bands are different for each dopant. The sharp emission properties show that the calcium stannate is a suitable host for rare-earth ion-doped phosphor material. Furthermore the influence of different rare-earth dopants, that is, Europium III, Neodymium III, Samarium III, Dysprosium III, and Terbium III, on thermally stimulated luminescence (TSL) of calcium stannate phosphor under the beta irradiation was discussed. Among these trivalent rare-earth-doped phosphors samarium-doped material showed maximum TSL sensitivity with favorable glow curve shape.Item Recyclability of CsPbBr3 quantum dot glass nanocomposites for their long-standing use in white LEDs(ROYAL SOC CHEMISTRY) Vahedigharehchopogh, N; Erol, E; Kibrisli, O; Genç, A; Ersundu, MÇ; Ersundu, AEThe embedding of CsPbBr3 perovskite quantum dots (PQDs) in an inorganic glass matrix not only protects them against chemical, thermal, and photodegradation but also provides an effective strategy to isolate toxic elements such as Pb from the environment for a long period of time. Herein, the recyclability of glass is another important feature that contributes to environmental sustainability. Hence, effective and efficient recycling technologies are needed for the widespread use of PQD glass nanocomposites (GNCs) in many commercial applications. However, studies on the recyclability of CsPbBr3 PQD GNCs have not been conducted so far. Therefore, in this work, we investigate the structural, thermal, optical, and photoluminescence properties of recycled CsPbBr3 PQD GNCs to assess their suitability as long-standing and reusable luminescent materials. For this purpose, the recyclability of GNCs is checked by three repeated melt-quenching and subsequent heat-treatment processes. Although the color emission properties of GNCs under the same heat-treatment conditions show a slight variation after each recycling step, PQD GNCs almost retain their PLQY even after the last recycling step. Ultimately, a prototype white light-emitting diode is constructed by coupling recycled PQD GNCs and a commercial red phosphor on top of a blue LED chip showing high-performance with CIE color coordinates of x = 0.3228, y = 0.3470 and a CCT value of 5920 K. The findings of this work reveal that the recyclability of PQD GNCs holds great promise for a more sustainable technology.Item Catholuminescence properties of rare earth doped CaSnO3 phosphor(PERGAMON-ELSEVIER SCIENCE LTD) Canimoglu, A; Garcia-Guinea, J; Karabulut, Y; Ayvacikli, M; Jorge, A; Can, NThe present study describes cathodoluminescence (CL) properties of CaSnO3 phosphors doped with Eu3+, Tb3+ and Dy3+ synthesized by a solid-state method. X-ray diffraction (XRD) patterns confirm that CaSnO3 sintered at 1200 degrees C exhibits orthorhombic structure. The evidence and rationale for two strong broad emission bands appeared at 360 and 780 nm for undoped CaSnO3 are presented. The CL measurements exhibit that the 4f-4f emissions from D-5(4) -> F-7(5) (490 nm), D-5(4) -> F-7(5) (544 nm), D-5(4) -> F-7(4) (586 nm) and D-5(4) -> F-7(3) (622 nm), assigned to possible transitions of Tb3+ ions are seen. The strongest one, observed at 544 nm, due to its probability of both magnetic and electric transitions make the sample emission green. Emissions at 480, 574, 662 and 755 nm were detected for the CaSnO3:Dy3+ and attributed to the transitions from the F-4(9/2) to various energy levels H-6(15/2), H-6(13/2), H-6(11/2) and H-6(9/2)+F-6(11/12) of Dy3+, respectively. CL spectra of Eu doped CaSnO3 reveal that there is a strong emission peak appeared at 615 am due to the electric dipole transition D-5(0) -> F-7(2) (red). Finally, our results show that the rare earth doped CaSnO3 have remarkable potential for applications as optical materials since it exhibits efficient and sharp emission due to rare earth ions. (C) 2015 Elsevier Ltd. All rights reserved.Item Solid state synthesis, characterization and optical properties of Tb doped SrSnO3 phosphor(ELSEVIER SCIENCE SA) Kotan, Z; Ayvacikli, M; Karabulut, Y; Garcia-Guinea, J; Tormo, L; Canimoglu, A; Karali, T; Can, NIn the present study, the structural and optical properties of SrSnO3 doped with Tb ions are reported. Novel SrSnO3:Tb3+ phosphors were conventionally synthesized using a solid state reaction process under a mildly reduced atmosphere (5% H-2 and 95% N-2). The crystal structures, morphologies and optical properties of the resultant materials have been characterised by experimental techniques such as X-ray Diffraction (XRD), Raman spectroscopy (RS), Photoluminescence (PL), Radioluminescence (RL) and Cathodoluminescence coupled to an ESEM (ESEM-CL). The new phosphor material has good crystallization without any impurity phases, which matches with the standard JCPDS files (No. 22-1442) from XRD analysis. The PL, RL and CL measurements taken at room temperature showed that the transitions of D-5(4) to F-7(J) (j = 6, 5, 4, 3) corresponding to the typical 4f -> 4f dipole forbidden intra-configurational transitions of Tb3+ are largely independent of the host material. The green emissions of the D-5(4) -> F-7(5) magnetic dipole transition at similar to 540 nm are predominant for three types of luminescence. PL emission spectra recorded in the temperature range from 10 K to 300 K were influenced by temperature. We report anomalies in the PL spectra of SrSnO3:Tb3+ compatible with a structural phase transition at 260 K while simultaneously exciting and cooling the sample. This work clearly confirms the existence of a phase transition discovered by Singh et al. in SrSnO3 at 270 K. (C) 2013 Elsevier B.V. All rights reserved.