• PDF / 66,707 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 10 Downloads / 228 Views

DOWNLOAD

REPORT

---

Luminescence of Lu2O3:Tm3+ nanoparticles Celso de Mello Donegá1,3, Eugeniusz Zych2, and Andries Meijerink1 Debye Institute, Dept. of Physics and Chemistry of Condensed Matter, Utrecht University, Princetonplein 1, 3508 TA Utrecht, The Netherlands. 2 Faculty of Chemistry, Wroclaw University, 14 Joliot-Curie Street, 50-383 Wroclaw, Poland. 3 On leave of absence from Dept. of Fundamental Chemistry, UFPE, Recife-PE, Brazil 1

ABSTRACT This paper presents for the first time a comparison between the luminescence properties (viz. emission and excitation spectra, lifetimes, and concentration quenching) of nanocrystalline and microcrystalline Lu2O3:xTm3+ (x= 0.1– 5 mol%). The results show that the most important difference between the two size regimes is the higher defect concentration in the nanoparticles. These defects give rise to a broadband emission ( λ max = 430 nm), and to partial quenching of the Tm3+ emission, in addition to the expected concentration quenching by cross-relaxation between Tm3+ ions. The defect concentration seems to be similar in all nanocrystalline samples, so that those with the lowest Tm3+ concentrations experience the most pronounced quenching. The nature of these defects is as yet unknown. The local structure around the Tm3+ ions is not noticeably different in the two size regimes. No evidence of phonon confinement or quantum size effects was observed in the Tm3+ luminescence. INTRODUCTION Nanostructured materials have attracted great interest in recent years because their properties are markedly different from those of bulk materials [1,2]. These differences arise from several effects (viz. larger surface to volume ratio, quantum confinement of charge carriers and geometrical confinement of phonons), which may have various impacts depending on the material and property under consideration [1,2]. The vast majority of the investigations have been focused on metals and semiconductors, rather than on insulators, even though many important commercial applications involve materials belonging to this latter class (e.g. phosphors for lighting and displays, lasers, scintillators, etc.). However, in the last few years there has been a growing interest in the properties of nanocrystalline lanthanide-doped insulating phosphors [3]. The most studied nanoparticulate material is Y2O3:Eu3+ [3-7], but other well-known phosphors, such as Y2SiO5:Eu3+ [8], YVO4:Eu3+ [9-10], Y2O3:Tb3+ [11], and LaPO4:Eu3+ or Ce3+,Tb3+ [9], prepared in a nanocrystalline form, have also been investigated. In this work we carried out for the first time a comparison between the luminescence of Lu2O3:Tm3+ in the bulk and nanocrystalline size regimes. EXPERIMENTAL DETAILS Nanocrystalline Lu2O3:xTm3+ (x= 0.1– 5 mol%) samples were prepared by a combustion technique using urea as a fuel and (Lu,Tm)(NO3)3 as an oxidizer. Typically, 4 mmol of (Lu,Tm)(NO3)3 and 6 mmol of urea were mixed with 1 mL water and the resultant solution was placed into a preheated furnace at 833 K for about 5 minutes in an ambient air atmosphere. The product was a fo