Energy conversion systems: Molecular architecture engineering of metal precursors and their applications to vapor phase
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Energy conversion systems: Molecular architecture engineering of metal precursors and their applications to vapor phase and solution routes Anna Lucia Pellegrino1 , Giacomo Lucchini2 , Adolfo Speghini2 , Graziella Malandrino1,a) 1
Dipartimento di Scienze Chimiche, Università di Catania and INSTM UdR Catania, Catania 95125, Italy Nanomaterials Research Group, Dipartimento di Biotecnologie, Università di Verona and INSTM UdR Verona, Verona 37134, Italy a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 3 July 2020; accepted: 28 August 2020
A careful engineering of the central metal coordination spheres provides adducts with excellent properties for application as precursors in vapor phase and solution processes. The family of precursors under study concerns the fluorinated metal-organic β-diketonates of alkaline, alkaline-earth and rare-earth metals adducted with a polyether, with general formula M(hfa)n·L (M = Ca, Na, Y, Yb, Er, Tm; Hhfa = 1,1,1,5,5,5 hexafluoroacetylacetone, L = diglyme or tetraglyme). Mass transport properties, such as volatility and thermal stability, of these adducts have been deeply analyzed through thermogravimetric analysis and differential scanning calorimetric measurements. These properties are rationalized in relation to the metal coordination sphere in the precursors and their applications. In particular, the precursors under focus have been applied to metal organic chemical vapor deposition and a combined sol–gel/spin-coating approach. Both methods allow us to obtain selectively and reproducibly CaF2 and NaYF4 phases with several combinations of lanthanide doping ions, using a proper mixture of fluorinated precursors. A careful optimization of both synthetic strategies is the key point for the production of different lanthanide-doped binary and multicomponent fluoride films, i.e., CaF2:Yb3+,Er3+; CaF2:Yb3+,Tm3+; CaF2: Yb3+,Er3+,Tm3+ and NaYF4:Yb3+,Er3+; NaYF4:Yb3+,Tm3+, with suitable morphologies, compositions and crystalline structures. The films show very promising upconversion properties, thus pointing to their appealing applications in photovoltaic systems and white light emission devices.
Introduction In the recent scenario of new functional materials for energetic applications, fluoride-based systems represent an emergent class of inorganic materials with application fields ranging from solar cells to phosphors in microelectronics [1, 2] from photocatalysis to nano-biomedicine devices [3, 4]. Particularly, lanthanidedoped fluoride films have been studied for energy conversion applications for their unique luminescent properties under light irradiation [5]. Fluoride systems, such as binary CaF2 and SrF2 or multicomponent NaYF4 and NaGdF4, have been studied as inorganic host materials with doping luminescent lanthanide ions (Ln3+: Yb, Er, Tm) in the form of nanoparticles or compact thin films for energy conversion processes [6, 7]. Depending on the active luminescence centers, energy conversion processes
take place as upconversion or downconve
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