Browsing by Author "Guinea J.G."
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Item Synthesis and luminescence properties of trivalent rare-earth element-doped calcium stannate phosphors(Taylor and Francis Inc., 2014) Karabulut Y.; Ayvacikli M.; Canimoglu A.; Guinea J.G.; Kotan Z.; Ekdal E.; Akyuz O.; Can N.The 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 ∼800 and ∼950 nm. 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. © 2014 Copyright Taylor & Francis Group, LLC.Item Cathodoluminescence and Raman characteristics of CaSO4:Tm3+, Cu phosphor(Elsevier, 2015) Ekdal E.; Guinea J.G.; Kelemen A.; Ayvacikli M.; Canimoglu A.; Jorge A.; Karali T.; Can N.The physical characterization and phosphor emission spectra are presented for CaSO4 doped with Tm and Cu. All spectral wavelengths are related to electronic transitions of Tm3+ ions. The powder X-ray diffraction pattern showed that the compound exhibits orthorhombic structure and all reflections were indexed without any other secondary impurity phases. Chemical and structural properties of the samples have been characterized by means of Raman spectroscopy and environmental scanning electron microscope (ESEM) with an attached X-ray energy dispersive system (EDS). Group frequencies concept is essential point to the interpretation of the bands due to the main SO4 vibrational units and these displayed main characteristic intensive Raman bands including typical strong intensity at 1016 cm-1 that corresponds to ν1SO4 vibrational mode. From the spatially-resolved cathodoluminescence (CL) spectrum, main emission bands of Tm3+ centered at 346, 362, and 452 nm, due to the respective transitions of 3P0→3H4, 1D2→3H6, 1D2→3F4 were clearly identified. The study is novel as no such CL-ESEM data are available for this doped compound. © 2015 Elsevier B.V. All rights reserved.Item The role of calcination temperature on structural and luminescence behaviour of novel apatite-based Ca2Y 8(SiO4)6O2: Ce3+,Tb3+ phosphors(Elsevier Ltd, 2017) Perhaita I.; Muresan L.E.; Silipas D.T.; Borodi G.; Karabulut Y.; Guinea J.G.; Ayvacikli M.; Can N.A series of novel apatite-based Ca2Y8(SiO4)6O2 phosphors doped with Ce3+ and Tb3+ were synthesized by a solid-state reaction method at different calcination temperatures and times. The comparative results of thermal analysis (TG-DTA), FTIR, X-ray diffraction (XRD) and environmental scanning electron microscope (ESEM) reveal that the firing temperature for Ca 2Y 8 (SiO4)6O2:Ce3+, Tb3+ was optimized to be 1200 °C. The systematic studies on the influences of thermal treatment conditions on photoluminescence (PL) and cathodoluminescence (CL) properties were also reported. The excitation spectra of Ca2Y8(SiO4)6O2:Ce3+, Tb3+exhibited one strong excitation band at 325 nm. The PL and CL results indicated that the violet-blue emission intensities about 400 nm from the Ce3+ and efficient green emission at 544 nm from Tb3+ were highly dependent on the calcination conditions. © 2017 Elsevier LtdItem Luminescence characteristics of Dy3+ incorporated zinc borate powders(Elsevier B.V., 2017) Portakal Z.G.; Dogan T.; Yegen S.B.; Küçük N.; Ayvacikli M.; Guinea J.G.; Canimoglu A.; Karabulut Y.; Topaksu M.; Can N.We have synthesized powder samples of Dy3+ doped zinc borates by nitric acid method. X-ray diffraction (XRD) and environmental scanning electron microscope (ESEM) techniques were utilized to examine the structure and morphological observation of the samples. Luminescence characteristics of the samples were investigated using room temperature (RT) cathodoluminescence (CL) and radioluminescence (RL) measurements under excitation with electron beam and X-rays, respectively. The presence of small amounts of Dy3+ incorporated in the host lattice does not affect the structure of the prepared samples remarkably. The CL and RL spectra showed the characteristic emissions of Dy3+(magnetic dipole transition of 4F9/2 →6H11/2 Blue; forced electric dipole transition of 4F9/2→ 6H13/2 Yellow; 4F9/2 →6H11/2 Red; 4F9/2 →(6H9/2 +6H11/2) infrared). Thermoluminescence (TL) method was also conducted to determine the effects of various concentrations of Dy3+ on the TL properties of ZnB2O4. The TL glow peak of beta irradiated ZnB2O4:Dy3+ phosphors is a well-defined and centered at around 96 °C with a constant heating rate of 2 °C/s. Initial rise method was employed to observed main TL glow curve for determining the activation energy (Ea) and the frequency factor (s). © 2017 Elsevier B.V.Item Luminescence studies of zinc borates activated with different concentrations of Ce and La under x-ray and electron excitation(Elsevier Ltd, 2017) Küçük N.; Ayvacikli M.; Akça S.; Yüksel M.; Guinea J.G.; Karabulut Y.; Canimoglu A.; Topaksu M.; Can N.Several ZnB2O4 powder samples having dopants concentrations of 0.1, 0.01, 0.04 wt% Ce and La were prepared using the nitric acid method via the starting oxides. Several complementary methods such as powder X-ray diffraction (XRD), thermal analyses environmental scanning electron microscopy (ESEM), Radioluminescence (RL) and Cathodoluminescence (CL) techniques were used. Unique luminescence properties of Ce doped ZnB2O4 powder samples are reported for the first time. A new luminescence bands appearing in red part of the spectrum and having all the characteristics of Ce3+ were obtained from RL results. Changing the Ce and La concentration of 0.01–0.1 wt% leads to an increase in RL and CL intensities of Ce3+ and La3+ ions and also CL emission spectra of ZnB2O4 show gradual shift towards longer wavelength. When we compare the luminescence intensity of the samples it is seen that Ce doped ZnB2O4 has the highest intense whereas La doped ZnB2O4 has the lowest one. However, emission spectra of both Ce and La doped samples kept unchanged. © 2017 Elsevier LtdItem Preparation and cathodoluminescence characteristics of rare earth activated BaAl2O4 phosphors(Elsevier Ltd, 2018) Benourdja S.; Kaynar Ü.H.; Ayvacikli M.; Karabulut Y.; Guinea J.G.; Canimoglu A.; Chahed L.; Can N.Undoped and Pr, Sm and Tb activated BaAl2O4 phosphors have been synthesized by solid state reaction method and combustion method. The structure and morphological observation of the phosphor samples were monitored by X-ray powder diffraction (XRD) and environmental scanning electron microscope (ESEM) coupled to an energy dispersive X-ray spectrometer (EDS). The all diffraction peaks are well assigned to standard data card (PDF♯17–306). Emission properties of the samples were explored using light emission induced by an electron beam (i.e cathodoluminescence, CL) at room temperature (RT). Undoped BaAl2O4 sample exhibits a broad defect emission from 300 to 500 nm from the aluminate defect centres. CL spectra recorded at room temperature display that the as-prepared BaAl2O4:Ln (Ln=Pr, Sm and Tb) phosphors exhibit different luminescence colors coming from different rare earth activator ions. The transition 4G5/2 → 6H7/2 located at 606 and 610 nm for Sm3+ can occur as hypersensitive transition having the selection rule ΔJ = ± 1. For the Tb3+ doped samples, they exhibit D45 green line emissions. The proposed luminescent mechanisms of all doped rare earth ions are also discussed. © 2018 Elsevier LtdItem Cathodoluminescence and thermoluminescence of ZnB2O4:Eu3+ phosphors prepared via wet-chemical synthesis(Elsevier Ltd, 2019) Dogan T.; Tormo L.; Akca S.; Kucuk N.; Guinea J.G.; Karabulut Y.; Ayvacikli M.; Oglakci M.; Topaksu M.; Can N.In present work, a series of Eu doped zinc borate, ZnB2O4, phosphors prepared via wet chemical synthesis and their structural, surface morphology, cathodoluminescence (CL) and thermoluminescence (TL) properties have been studied. Phase purity and crystal structure of as-prepared samples are confirmed by X-ray diffraction measurements (XRD) and they were well consistent with PDF card No. 39-1126, indicating the formation of pure phase. The thermoluminescence (TL) behaviors of Eu activated ZnB2O4 host lattice are studied for various beta doses ranging from 0.1 to 10 Gy. The high-temperature peak of Eu activated sample located at 192 °C exhibited a linear dose response in the range of 0.1–10 Gy. Initial rise (IR) and peak shape (PS) methods were used to determine the activation energies of the trapping centres. The effects of the variable heating rate on TL behaviour of Eu activated ZnB2O4 were also studied. When excited using an electron beam induced light emission (i.e cathodoluminescence, CL) at room temperature (RT), the as-prepared phosphors generate reddish-orange color due to predominant emission peaks of Eu3+ ions located at 576–710 nm assigned to the 5D0→7FJ (J=1,2,3, and 4) transitions. The maximum CL intensity for Eu3+ ions at 614 nm with transition 5D0→7F2 was reached Eu3+ concentration of 5 mol%; quenching occurred at higher concentrations. Strong emission peak for Eu3+ ions at 614 nm with transition 5D0→7F2 is observed. The CL experimental data indicate that ZnB2O4:Eu3+ phosphor as an orange-red emitting phosphor may be promising luminescence materials for the optoelectronic applications. © 2018 Elsevier Ltd and Techna Group S.r.l.Item Cathodoluminescence properties of La2MoO6:Ln3+ (Ln: Eu, Dy, and Sm) phosphors(Elsevier Ltd, 2020) Ayvacikli M.; Kaynar Ü.H.; Karabulut Y.; Guinea J.G.; Bulcar K.; Can N.La2MoO6 orange-red phosphors with high efficiency incorporated with Eu, Dy and Sm have been synthesized through a gel combustion method. The influences of rare earth doping in synthesized samples were analysed by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and cathodoluminescence. Rare earth doped La2MoO6 samples show strong emission bands in the range of 400–750 nm and optimal doping concentration for all samples was 2 mol%. La2MoO6 host doped Eu ion showed intense and predominant emission peaks in 450–750 nm range. The electrical multipolar interaction contributed to the non-radiative energy transfer between Eu3+ ions in La2MoO6 host matrix. Sm doped La2MoO6 host exhibited orange-red CL emission peaks at 564, 608, 652 and 708 nm La2MoO6:Dy3+ phosphor displayed emissions at 484, 574 and 670 nm, respectively. The observed intense and sharp emission peaks indicate that La2MoO6 is promising host for lanthanides doped phosphor materials in the applications of optoelectronic. © 2020 Elsevier LtdItem Cathodoluminescence and photoluminescence properties of Dy doped La2CaB10O19 phosphor(Elsevier B.V., 2020) Ayvacikli M.; Kaynar Ü.H.; Karabulut Y.; Guinea J.G.; Dogan T.; Can N.In this study, we report a detailed analysis of the photoluminescence (PL) and cathodoluminescence (CL) properties of La2CaB10O19 (LCB) doped with Dy ion. Dy doped LCB materials were successfully synthesized using a sol-gel combustion method. Dy doped LCB has the monoclinic structure with lattice parameters a = 11.02067 Å, b = 6.55755 Å, c = 9.10541 Å and α = γ = 90.00, and β = 91.49°. Under the excitation by a low voltage electron beam and pulse laser at 349 nm, the LCB:Dy3+ phosphor produces the characteristic emission bands of Dy3+ due to intra-configuration transitions of 4F9/2 → 6H15/2 (480 nm, blue), 4F9/2 → 6H13/2 (574 nm, yellow), 4F9/2 → 6H11/2 (662 nm, red) and 4F9/2 → 6H9/2 (752 nm, red). The concentration quenching phenomenon was observed in both CL and PL measurements and optimum doping concentration was estimated to be 2%. We suggest that the concentration quenching mechanism of intense yellow emission at 574 nm was attributed to dipole-dipole interaction for both CL and PL. © 2020 Elsevier B.V.Item Comprehensive study of photoluminescence and cathodoluminescence of Eu and Tb doped Mg2SiO4 prepared via a solid-state reaction technique(Elsevier B.V., 2020) Ucar Z.G.P.; Akca S.; Dogan T.; Halefoglu Y.Z.; Kaynar U.H.; Ayvacikli M.; Guinea J.G.; Topaksu M.; Can N.We report narrow-band green-red emitting Mg2SiO4 phosphors successfully synthesized through solid-state reaction method, and the cathodoluminescence (CL) and photoluminescence (PL) properties of the samples were investigated in detail. Under electron beam and 275 nm excitation, Mg2SiO4 phosphors doped with various Eu3+ and Tb3+ concentrations in the range of 1 mol % up to 10 mol % exhibit typical green and red emissions, respectively. Tb doped samples were efficiently excited by a low voltage electron beam and UV light, yielding several emission peaks between 370 and 760 nm, and produced a bright green light peaking at 541 nm due to the 5D4 →7F5 transition. Eu3+ doped samples exhibited CL and PL emission spectra from 5D0 to 7Fj manifold transitions of Eu3+. A strong red-light emission peaking at 610 nm also supports the incorporation of Eu3+ ions. A concentration quenching effect was observed and discussed for both phosphors. The optimal doping concentration of Eu3+ and Tb3+ doped phosphors was 7 mol %. In view of the outstanding performance in the PL and CL, the Mg2SiO4:Eu3+, Tb3+ can be considered as a promising green and red phosphor in solid-state lighting applications. © 2020 Elsevier B.V.Item Structural and temperature dependence luminescence characteristics of RE (RE=Eu3+, Dy3+, Sm3+ and Tb3+) in the new gadolinium aluminate borate phosphor(Elsevier Ltd, 2023) Madkhali O.; Kaynar Ü.H.; Alajlani Y.; Coban M.B.; Guinea J.G.; Ayvacikli M.; Pierson J.F.; Can N.GdAl3(BO3)4:Dy3+, Sm3+, Eu3+, and Tb3+ samples were successfully achieved via a sol-gel combustion method. The observed XRD analysis confirms the formation of the desired GAB host, indicating rhombohedral structures that agree well with JPCD card number 72–1985. The FTIR analyses show the detection of B − O stretching and B − O − B bending modes as well as Al − O and Gd − O bonds in the phosphor samples. Energy dispersive spectroscopy (EDS) analysis reveals that Sm, Eu, Dy, and Tb have been successfully doped into GdAl3(BO3)4. The observed broad intrinsic luminescence band can be caused by oxygen-induced luminescence defects in the GAB host with hydrous precursors. The luminescence properties of rare earth ion-doped GdAl3(BO3)4 samples are analysed by photoluminescence spectra, showing their optimal doping concentrations and critical distances of Dy3+, Eu3+, Sm3+ and Tb3+ are 2 wt% − 25.8 Å, 7 wt% − 17 Å, 1 wt% − 32.59 Å, and 7 wt% − 17.03 Å. Additionally, the energy transfer mechanism for luminescence quenching was determined as dipole-dipole (for Dy3+, Eu3+, and Tb3+) or dipole-quadrupole (for Sm3+) and the cross-relaxation process. GdAl3(BO3)4 samples obtained by doping with different RE3+ ions exhibit intense light emissions with different colors originating from different RE3+ ions under 349 nm excitation. When doped with different concentrations of RE3+ ions, the luminescence properties of the samples changed. The synthesized luminescence materials have potential applications in lighting and display technologies. © 2023 Elsevier Ltd and Techna Group S.r.l.Item Structural and thermal insights into the luminescent behavior of Dy³⁺-Doped BaZrO₃ with alkali metal codopants under UV radiation(Elsevier Ltd, 2025) Arslanlar Y.T.; Alajlani Y.; Coban M.B.; Kaynar U.H.; Aydin H.; Örücü H.; Guinea J.G.; Can N.This study investigates the structural, thermal, and photoluminescent properties of Dy³⁺-doped BaZrO₃ (BZO) perovskites, synthesized via a co-precipitation method, incorporating alkali metal codopants (Li⁺, Na⁺, and K⁺). X-ray diffraction (XRD) analysis confirmed the retention of the cubic perovskite phase following doping, with Rietveld refinement further revealing minor lattice distortions due to Dy³⁺ incorporation. The Williamson-Hall (W–H) analysis revealed average crystallite sizes of 53 nm and 66 nm for undoped and 0.01 Dy³⁺-doped BaZrO₃, respectively, with corresponding micro-strain values of 1.79 × 10⁻³ and 1.81 × 10⁻³, suggesting lattice distortions due to incorporation of Dy³⁺. Fourier transform infrared (FTIR) spectroscopy confirmed the cubic perovskite structure and subtle structural modifications upon doping. Notably, the absence of moisture-related peaks highlights the effectiveness of the synthesis process, including rigorous drying and calcination steps that prevented hydrous species. Photoluminescence (PL) analysis of Dy³⁺-doped BaZrO₃ exhibited three prominent emission peaks at 452 nm, 573 nm, and 656 nm under 368 nm excitation. These peaks correspond to the characteristic intra-4f electronic transitions of Dy³⁺ ions, specifically, 4I13/2 to 6H15/2, 4F9/2 to 6H13/2, and 4F9/2 to 6H11/2, representing blue, yellow, and red emissions, respectively. Photoluminescence decay studies showed multi-exponential behavior, with the average lifetime decreasing from 641 μs in undoped BZO to 492 μs in Dy³⁺-doped samples attributed to enhanced non-radiative recombination pathways. Among the codopants, Li⁺ demonstrated the most significant improvement in luminescence intensity and thermal stability by mitigating defects and optimizing charge compensation. © 2025 Elsevier Ltd