Luminescent properties of fluorophosphate glasses with lead chalcogenides molecular clusters E.V. Kolobkova, D.S. Kukushkin, N.V. Nikonorov, T.A. Shakhverdov, A.I. Sidorov n , V.N. Vasiliev ITMO University, 4 Birzhevaya line, St. Petersburg 199034, Russia article info Article history: Received 15 July 2014 Received in revised form 25 January 2015 Accepted 5 February 2015 Available online 14 February 2015 Keywords: Luminescence Molecular cluster Lead chalcogenide Fluorophosphate glass abstract Fluorophosphate glasses containing lead, selenium, and sulfur exhibit an intense luminescence in the 400–620 nm spectral region when excited by the 240–420 nm radiation. This luminescence is due to the presence of (PbSe) n and/or (PbS) n molecular clusters in the glasses, which appear in the as-prepared glasses before quantum dots formation. The thermal treatment at temperatures less than the glass transition temperature results in the red-shift of the luminescence bands and in an increase in the luminescence intensity. Heating the thermally treated glass samples leads to the reversible thermal quenching of the luminescence. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Composite optical materials with PbSe and PbS quantum dots are used widely now in optics and photonics [1–12]. Such materials exhibit the luminescent properties in the near IR (see, for example, [4]) and also non-linear optical properties [5,6]. The procedure of synthesizing the lead chalcogenide quantum dots in glasses consists in the thermal treatment at a certain temperature higher than the glass transition one of a glass containing before the synthesis lead, selenium, and sulfur. The thermal diffusion of lead ions and chalcogen atoms leads to the formation and growth of quantum dots in glass. Variations in the thermal treatment temperature and duration make it possible to change the quantum dot dimensions in a wide range. It is evident that the lead chalcogenide structures should pass, in the course of their forma- tion and growth, a stage at which their size remains less than 1 nm. This stage corresponds to the occurrence, in a glass, of lead chalcogenide structures in the form of subnanosized molecular clusters whose properties can considerably differ from the proper- ties of quantum dots. For the last years, a scientific interest in the metal and semiconductor molecular clusters (MCs) has increased rapidly [13,14]. MCs are of interest also from the practical viewpoint because some of MC types exhibit an intense luminescence in the visible. In some cases, the MCs arise in glasses during the thermal treatment; in other cases, they are formed directly in the course of the glass synthesis. The luminescent properties of silver molecular clusters Ag n in oxyfluorine and silicate glasses were investigated in Refs. [15–21]. In Refs. [22–24], the luminescent properties of (CuCl) n and (Cu 2 O) n clusters in potassium–alumina– borate and silicate glasses were studied. The investigation of silver and gold molecular clusters in the metal-organic compounds was performed in Refs. [25–30]. In spite of enormous amount of research works devoted to the investigation of lead and cadmium chalcogenide quantum dots, there are quite few sources describing the corresponding MCs properties. In Refs. [31,32] the structure of the stable (CdSe) n (n ¼ 1–4) and (X- CdS) n (n ¼ 4–16, X¼ Na, K, Cl, and Br) molecular clusters was investigated by the computer modeling. In Ref. [33], the structure of CdSe molecular clusters was studied by an NMR method. The structure of Cd 2 O 2 Se and CdO 2 Se molecular clusters was investigated in Ref. [34] by X-ray absorption spectroscopy. It was shown in Refs. [35–40] that the Se 2 and Se 2 À molecular clusters are present in both glasses and sodalite. Such MCs exhibit the luminescence bands at 480 and 710 nm. To our opinion there are no publications in which the lead chalcogenide MCs properties are described. In our experiments for as-prepared fluorophosphate (FP) glasses containing lead, selenium, and sulfur we observed an intense luminescence in the visible, excited by the UV radiation before quantum dots formation. In the reference samples without lead only very weak luminescence was observed, which can be Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2015.02.009 0022-2313/& 2015 Elsevier B.V. All rights reserved. n Correspondence to: Kronverkskii pr. 49, St. Petersburg 197101, Russia. Tel.: +79119205938. E-mail address: aisidorov@qip.ru (A.I. Sidorov). Journal of Luminescence 162 (2015) 36–40