Spectroscopic and structural properties of polycrystalline Y 2 Si 2 O 7 doped with Er 3 þ L. Marciniak a,n , D. Hreniak a , W. Strek a , F. Piccinelli b,n , A. Speghini b , M. Bettinelli b , M. Miritello c,n , R. Lo Savio c , P. Cardile c , F. Priolo c a Institute for Low Temperature and Structure Research, Polish Academy of Sciences, Wroclaw, Poland b Laboratorio di Chimica dello Stato Solido, DB, Università di Verona and INSTM, UdR Verona, Strada Le Grazie 15, 37134 Verona, Italy c CNR-IMM MATIS and Dipartimento di Fisica e Astronomia, Università di Catania, Via S. Sofia 64, 95123 Catania, Italy article info Article history: Received 18 December 2014 Received in revised form 6 February 2015 Accepted 9 February 2015 Keywords: Silicates Nanocrystals Rare earths Size effect abstract Powders of yttrium disilicate (Y 2 Si 2 O 7 ) doped with Er 3 þ have been prepared by the sol–gel method. The structure of the obtained powders has been determined. Room temperature emission spectra have been recorded and excited state decay profiles have been analyzed. Differences between the spectroscopic properties of Er 3 þ in monoclinic α-Y 2 Si 2 O 7 (space group P-1) and β-Y 2 Si 2 O 7 (space group C2/m) polymorphs have been investigated and shown. The significant broadening of the emission spectra recorded for the α phase compared to the one for the β phase was discussed in terms of higher number of Y 3 þ sites (4) present in the α phase with respect to only one Y 3 þ site in the case of β phase. The higher value of the luminescence decay time of β phase (11.2 ms) compared to the α phase (8.5 ms) is associated with the higher site symmetry of β-Y 2 Si 2 O 7 . Moreover it was found that Er 3 þ concentration affects the shape of the 4 I 13/2 - 4 I 15/2 emission band. It results in changes of the relative emission intensities of peaks localized at 1527 nm and 1532 nm; this indicates changes of the Y 3 þ sites occupation on increasing the Er 3 þ concentration. The luminescence lifetime was observed to decrease with the increase of Er 3 þ concentration. The spectroscopic results have been compared with the ones relative to thin films of Y 2 Si 2 O 7 :Er 3 þ with a similar composition. The lower value of the luminescence decay time observed for thin films compared to the powder of α phase was explained with the changes of the particles packing resulting in the change of the effective refractive index. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Polycrystalline yttrium silicates have attracted great attention, due to many advantages such as a high resistance to radiation damages [1–3] and thermal and chemical stability [4,5]. Yttrium silicates are among the most interesting hosts for rare-earth (RE) ions, which substitute easily Y 3 þ ions [1–3,6–19]. These hosts exhibit also a minimal effect of nuclear spins of the constituent elements which results in narrow homogeneous emission lines of the dopant RE ions [7–9].Y 2 SiO 5 (YSO) doped with Ce-ions (YSO: Ce 3 þ ) is one of the best low-voltage phosphors for field emission displays due to its high efficiency, color purity and stability [2,3, 9–11,18], YSO:Tb 3 þ is considered one of the best green emitting cathodoluminescent phosphors [1] and YSO:Eu 3 þ as a promising phosphor for high resolution applications [13–15,19]. Moreover in more recent years, erbium compounds [20–24] and erbium doped yttrium silicates [25–27] have attracted considerable attention also as active medium of small-size on-chip amplifiers and lasers around the telecom wavelength in silicon photonics. Indeed the performances of the planar waveguide amplifiers based on Er- doped SiO 2 amorphous (EDFA) are limited by the number of optically active Er ions since its low solubility, about 10 20 cm À3 , instead the introduction of yttrium silicates can permit to incor- porate higher Er density up to 10 22 cm À3 and all the Er ions have been demonstrated to be optically active [21,25]. However the maximum Er optical efficiency strongly depends on Er content and host preparation, since the specific sensitivity of Er 3 þ on the host material and the strongly concentration depending co-operative processes occurring between Er 3 þ ions, dramatically change the spectroscopic properties. But very few detailed works have been reported for Y 2 Si 2 O 7 doped with RE ions (rare-earth pyrosilicates or disilicates) [17–21,25,28,29]. The main reason for this is that its different polymorph structures naturally lead to relatively broad emissions originating from ions placed in different symmetry sites. Unfortunately, Y 2 Si 2 O 7 has been reported to form as many as five polymorphs: y, α, β, γ, and δ [30–33], in many cases co-existing ones, stabilized by different impurities and strongly depending on Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2015.02.015 0022-2313/& 2015 Elsevier B.V. All rights reserved. n Corresponding authors. E-mail addresses: L.Marciniak@int.pan.wroc.pl (L. Marciniak), fabio.piccinelli@univr.it (F. Piccinelli), maria.miritello@ct.infn.it (M. Miritello). Please cite this article as: L. Marciniak, et al., J. Lumin. (2015), http://dx.doi.org/10.1016/j.jlumin.2015.02.015i Journal of Luminescence ∎ (∎∎∎∎) ∎∎∎–∎∎∎