Browsing by Author "Vahedigharehchopogh, N"

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    Ultra-stable Eu3+/Dy3+co-doped CsPbBr3 quantum dot glass nanocomposites with tunable luminescence properties for phosphor-free WLED applications
    Erol, E; Vahedigharehchopogh, N; Ekim, U; Uza, N; Ersundu, MÇ; Ersundu, AE
    Colloidal 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.
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    A straightforward approach for high-end anti-counterfeiting applications based on NIR laser-driven lanthanide doped luminescent glasses
    Vahedigharehchopogh, N; Kibrisli, O; Erol, E; Ersundu, MC; Ersundu, AE
    The increase in forgery in documents and authentic products has motivated the search for new high-end anti-counterfeiting strategies. Various chameleon-like luminescent materials such as up-conversion nanoparticles or perovskite nanocrystals have drawn attention due to their favorable properties. However, these materials are fabricated through complex processes and often suffer from system instability. In this work a facile and inexpensive approach for color tuning of thermally and chemically stable Ho3+/Tm3+/Yb3+ doped tellurite glasses is experimentally demonstrated for the first time. The emission band ratios are successfully manipulated by focusing/defocusing the NIR laser beam irradiating the glass samples. Impressive up-conversion quantum yield values up to 4.56% are obtained along with high lifetime values from similar to 100 to 200 microseconds. As proof of concept, a series of anti-counterfeiting patterns are created using the screen-printing method and different emission colors are observed by easily changing the distance between the sample and the laser focal point. The applicability of the presented strategy along with the remarkable properties of the studied lanthanide doped glasses proves the capability of these materials to be used in anti-counterfeiting applications.
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    Recent progress in lanthanide-doped luminescent glasses for solid-state lighting applications-a review
    Erol, E; Vahedigharehchopogh, N; Kibrisli, O; Ersundu, MÇ; Ersundu, AE
    Nowadays, solid-state white light-emitting diodes (wLEDs) have attracted remarkable attention for applications in general lighting, displays and numerous electronical devices due to their eminent efficiency, longer lifetime and higher mechanical durability compared to traditional incandescent and fluorescent lights. In current commercial wLEDs, a combination of Y3Al5O12:Ce3+ yellow phosphor with blue LED chip and epoxy resin is generally used to generate white light. However, there are some considerable frailties mostly originated from phosphor and resin such as, degradation upon heat, and moisture, inhomogeneous spectral distribution, and poor color rendering capability. Therefore, phosphor embedded glass-ceramics have been developed as a promising way to obtain durable solid-state lighting devices. However, in these methods, there is a greater risk of reactions between the phosphor material and the glass host. At this point, lanthanide-doped luminescent glasses have drawn great attention as a new generation phosphor and/or epoxy free white-light-emitting source owing to their favorable properties including high thermal and chemical stability, high transparency, and easy manufacturing process. This review article aims to comprehensively summarize the recent progress in singly (i.e., Dy3+, Eu2+), doubly (i.e., Dy3+/Eu3+, Dy3+/Tm3+, Dy3+/Ce3+, Ce3+/Sm3+, Ce3+/Tb3+) and triply (i.e., Ce3+/Tb3+/Mn2+, Eu3+/Tb3+/Tm3+, Ce3+/Tb3+/Eu3+, Tm3+/Tb3+/Sm3+, Ce3+/Dy3+/Eu3+, Ho3+/Tm3+/Yb3+, Er3+/Tm3+/Yb3+) lanthanide-doped glasses for solid-state lighting applications through down-shifting and up-conversion emissions. Theoretical background including energy transfer mechanisms, glass synthesis methods, radiative and colorimetric properties are given in details. Finally, various effective strategies are highlighted that minimize the critical challenges associated with lanthanides-such as providing energy transfer from quantum dots or nanoparticles to lanthanides, and doping lanthanides in low phonon energy glass-to improve the white light emission of luminescent glasses and broaden their application areas.
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    The synergistic effect of Er3+ and Ho3+ on temporal color tuning of upconversion emission in a glass host via a facile excitation modulation technique for anti-counterfeiting applications
    Erol, E; Kibrisli, O; Vahedigharehchopogh, N; Ersundu, MÇ; Ersundu, AE
    Lanthanide-doped upconversion luminescent materials are highly promising for diverse applications, e.g., solid-state lighting, volumetric displays, and anti-counterfeiting, owing to their unique optical feature of color-tunable emission under near-infrared excitation. Hence, in this study, emission color tuning of Er3+/Ho3+ ions in a fixed glass host is investigated via a facile excitation modulation technique. The upconversion emission color from green to yellowish is tuned successfully by regulating the frequency of the irradiation source. The population and depopulation rates of related transitions are investigated through time-resolved photoluminescence and Judd-Ofelt analysis in order to elucidate the proposed mechanism of color tuning. Upconversion quantum yield values are measured in the range of 0.12 to 0.17% for a better comparison of the emission properties. Additionally, thermal, and structural properties are investigated to reveal the favorable properties of the selected tellurite glass host. Ultimately, several patterns are designed and constructed by a screen-printing technique using powdered glass to demonstrate its suitability as a multicolor imaging method for anti-counterfeiting applications. The temporal color tuning of upconversion emission via a facile excitation modulation technique in a glass host clearly indicates that the proposed Er3+/Ho3+ co-doped glasses can be potentially applied in the state-of-the-art technologies, especially for anticounterfeiting purposes.
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    Recyclability of CsPbBr3 quantum dot glass nanocomposites for their long-standing use in white LEDs
    Vahedigharehchopogh, N; Erol, E; Kibrisli, O; Genç, A; Ersundu, MÇ; Ersundu, AE
    The 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.