Investigation of spectroscopic properties and energy transfer between Ce and Dy in (Lu 0.2 Gd 0.8 À x À y Ce x Dy y ) 2 SiO 5 single crystals A. Strzęp a,n , I.R. Martin b,c , M. Glowacki d , W. Ryba-Romanowski a , M. Berkowski d , C. Pérez-Rodríguez b,c a Institute of Low Temperature and Structure Research PAS, Wroclaw, Poland b Faculty of Physics, Universidad de La Laguna, S/C de Tenerife, Spain c Malta Consolider Team and Instituto de Materiales y Nanotecnología (IMN), Universidad de La Laguna, S/C de Tenerife, Spain d Institute of Physics PAS, Warsaw, Poland article info Article history: Received 17 November 2014 Received in revised form 27 April 2015 Accepted 10 May 2015 Available online 29 May 2015 Keywords: Luminescence and amplification measure- ments Single crystal Energy transfer abstract In this paper we present results of spectroscopic investigations of single crystals with general formula (Lu 0.2 Gd 0.8 Àx Ày ) 2 SiO 5 codoped with x% of Ce 3 þ and y% of Dy 3 þ ions. Investigated materials exhibit strong optical anisotropy what can be easily observed in polarized absorption and emission spectra. Based on room temperature polarized absorption spectra calculations in framework of phenomenological Judd– Ofelt model was carried out. Intensity parameters Ω t were evaluated to be Ω 2 ¼7.08 ( 70.39), Ω 4 ¼2.76 ( 70.44), and Ω 6 ¼3.36 ( 70.21) [10 À20 cm 2 ] for sample doped with 1% of cerium and Ω 2 ¼10.72 ( 70.33), Ω 4 ¼1.98 ( 70.37), and Ω 6 ¼2.11 ( 70.18) [10 À20 cm 2 ] for sample doped with 3% of cerium. Influence of cerium admixture on Judd Ofelt intensity parameters is discussed. Value of experimental lifetime of 4 F 9/2 multiplet of Dy 3 þ ion in sample doped with 1 at% Ce is 0.5 ms (τ rad ¼0.45 ms), while for sample doped with 3 at% of Ce, experimental lifetime is 0.45 ms (τ rad ¼0.43 ms). Absorption bands lo- cated between 440 and 460 nm, can be utilized for optical pumping of material by GaN laser diodes. Intense and broad emission bands at 465–495 and 560–590 nm, with experimental branching ratio strongly depending on polarization, give high chance for obtaining white luminophore, due to appropiate mixing of blue and yellow luminescence. By means of a pump and probe experiment optical amplifi- cation was demonstrated in the codoped sample with 1 at% of Ce and 1 at% Dy at 575 nm corresponding to the emission of Dy 3 þ with a high net gain coefficient of 34 cm À1 . Such high amplification was ob- tained under 359 nm excitation (at the maximum of intense absorption band of Ce 3 þ ions). & 2015 Elsevier B.V. All rights reserved. 1. Introduction Oxyorthosilicates with general formula RE 2 SiO 5 form a group of known but still intensively studied materials. Lu 2 SiO 5 or Gd 2 SiO 5 crystals doped with cerium, usually denoted as LSO:Ce or GSO:Ce respectively, belong to most common scintillation materials [1]. RE 2 SiO 5 doped with lanthanide ions such as Nd 3 þ , Sm 3 þ , Eu 3 þ , Tb 3 þ , Dy 3 þ , Er 3 þ ,and Yb 3 þ can find potential application as phosphors [2] or laser materials [3]. Crystal structure of RE 2 SiO 5 (RE ¼ Sc 3 þ ,Y 3 þ , Gd 3 þ ,and Lu 3 þ ) belongs to monoclinic system. Usually aforementioned oxyorthosilicates crystallize in C2/c space group. Exception is Gd 2 SiO 5 which crystallizes in P2 1 /c space group. LSO and GSO systems exhibit continuous solubility in solid state; however, due to different space groups of pure components, phase change must be forced for exact value of lutetium concentration. For (Lu x Gd 1 Àx ) 2 SiO 5 solid state solution this phase change occurs when x is less than 0.17 [4]. A great disadvantage of solution crystallized in P2 1 /c space group, contrary to C2/c, is the tendency to crack along cleavage plane, what leads to problems during mechanical processing of this material. A very high melting temperature (T m ¼ 2060 °C) which is close to thermal breakdown of iridium crucible and heat insulation of stabilized zirconia ceramics is a disadvantage of pure Lu 2 SiO 5 crystals. Introduction of solid state solution of GSO and LSO gives two advantages. Firstly melt temperature of solution can be reduced by ca. 200 K in comparison to melt temperature of pure LSO [4]. Secondly huge amount of expensive Lu 2 O 3 can be substituted by relatively cheaper Gd 2 O 3 . Sidletskiy et al. [5] discuss other practical aspects of substitution of Lu ions by the Gd ones. They suggested that such substitution will efficiently reduce the difference between ionic radius of Lu 3 þ and lanthanide ions from beginning of lanthanide series such as Ce 3 þ or Pr 3 þ , which will lead to smaller Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2015.05.013 0022-2313/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. Journal of Luminescence 166 (2015) 304–312