Optical spectroscopy of Nd 3 þ ions in a nanostructured glass matrix E.O. Serqueira a , N.O. Dantas a , V. Anjos b , M.A. Pereira-da-Silva c,d , M.J.V. Bell b,n a Laborato ´rio de Novos Materiais Isolantes e Semicondutores (LNMIS), Instituto de Fı ´sica, Universidade Federal de Uberlˆ andia, 38400-902 Uberlˆ andia-MG, Brazil b Grupo de Espectroscopia de Materiais, Departamento de Fı ´sica, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora-MG, Brazil c Instituto de Fı ´sica de S ~ ao Carlos, USP, S ~ ao Carlos, SP 13560-250, Brazil d Centro Universita ´rio Central Paulista, UNICEP, S ~ ao Carlos, SP 13563-470, Brazil article info Article history: Received 7 November 2010 Received in revised form 1 March 2011 Accepted 11 March 2011 Available online 21 March 2011 Keywords: Nd 3 þ CdS Glasses Luminescence Judd–Ofelt abstract This paper presents the optical characterization of Nd 3þ ions in nanostructured SiO 2 –Na 2 CO 3 –Al 2 O 3 –B 2 O 3 (SNAB) CdS glass, synthesized by fusion. Radiative properties of the glass were determined by absorption, luminescence spectroscopy and lifetime measurements. Nd 3þ emission enhancement and quenching were investigated in the presence of CdS nanocrystals. Nd 3þ -emission quenching was attributed to upconversion mechanisms and nonradiative processes such as multiphonon decay and energy transfer, while the Nd 3þ -emission enhancement was due to energy transfer from the CdS nanocrystals. Changes in the chemical environment around CdS nanocrystals were also confirmed by Judd–Ofelt calculations. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Glass systems codoped with rare earth (RE) ions and semi- conductor nanocrystals (NCs) have attracted great research inter- est because of their applications in optical systems [1–3]. The influence of semiconductor NCs on the radiative properties of RE ions has been demonstrated, particularly with Eu 3 þ , Tb 3 þ , Er 3 þ , Pr 3 þ and Nd 3 þ [4–6]. The importance of the research relates to the possibility of energy transfer from semiconductor nanocrystals (NCs) to rare earth ions, which may result in enhancement of the rare earth luminescence. The effect is due to the higher absorption cross-section of semiconductor NCs when compared to those of rare earth ions [7]. Particularly, the absorption band of CdS NCs can be tuned according to CdS NCs dimensions. It means that resonance with Nd 3þ bands can be achieved, increasing the probability of energy transfer to Nd 3þ . As the absorption bands of CdS NCs are broader than the ones of Nd 3þ , it ensures a better match in wavelength of the pump sources (usually diode lasers) for the achievement of opto-electronic devices, such as laser active media [8, 9], optical amplifiers [10], microchips [11] and planar waveguides due to their emission in the near infrared range at 1060 nm [3, 12, 13]. SNAB glass was chosen as host to CdS because it is suitable for the growth of high quality CdS and due to its transparency to the UV through near-IR, where energy transfer processes take place and the most important Nd 3þ absorption and emission bands occur. SNAB host has been previously investigated. Ref. [6] exposes the energy transfer process from CdS NCs to Nd 3þ ions in the present samples. Moreover, a study of the thermal properties was performed and revealed that CdS nanoparticles reduce the thermal diffusivity of the samples [14]. Nevertheless there is a lack of data from analysis, based on the Judd–Ofelt Theory, regarding the spectroscopic properties of RE ions embedded in glass systems codoped with semiconductor NCs [15–20]. It is well known that this type of analysis produces the so called Judd–Ofelt parameters O l (l ¼ 2, 4, 6), which can be used to find spontaneous emission probability, branching probability (branching ratio), emission cross-section, radiative lifetime and effective linewidth. These parameters can also be used to predetermine if an RE ion host material is suitable for optical device applications [15,21–24]. The main objective of this research was to evaluate the spectroscopic fluorescence parameters of Nd 3 þ ions embedded in a SiO 2 –Na 2 O–Al 2 O 3 –B 2 O 3 glass system in the presence of CdS NCs, as a function of thermal annealing time. Electronic dipole transitions are permitted due to the mixture of opposite parity wave-functions in the 4f N configuration of rare earth ions. According to the Judd–Ofelt Theory, electric dipole oscillator strength, between initial 9f n ½aSLJS and final states 9f n ½a 0 S 0 L 0 J 0 S, is given by f ED ðJ, J 0 Þ¼ 8p 2 mc 3h 1=l ð2J þ1Þ w X l ¼ 2, 4, 6 O l f n ½aSLJ    U ðlÞ       f n ½a 0 S 0 L 0 Jf n ½a 0 S 0 L 0 J 0          2 , ð1Þ where m is the electron mass, c the speed of light, 1/l is the wave number, h the Planck constant, J the angular moment of the initial Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2011.03.032 n Corresponding author. E-mail address: mjbell@fisica.ufjf.br (M.J.V. Bell). Journal of Luminescence 131 (2011) 1401–1406