Elsevier

Journal of Luminescence

Volume 202, October 2018, Pages 354-362
Journal of Luminescence

A study of optical properties of Tm3+ ions in Y2Te4O11 microcrystalline powder

https://doi.org/10.1016/j.jlumin.2018.05.079Get rights and content

Abstract

The Y2-xTe4O11 (x = 0.1, 0.5, 1.0, 2.0 and 5.0 at%) microcrystalline powders were successfully synthesized by a conventional solid state reaction method. Optical absorption (300 K) and fluorescence spectra (300 K) as well as fluorescence decay curves (300 K) of the emitting levels of Tm3+ ion in Y2Te4O11 powders are presented and analyzed in details. The Judd-Ofelt theory was applied to analyze experimental data for the quantitative determination of phenomenological Ωλ (λ = 2, 4, 6) parameters, radiative transition probabilities (A), branching ratios (β) of luminescence and radiative lifetimes (τrad) of the 1D2, 1G4, 3H4 and 3F4 levels. The observed non-exponential decays nature and concentration quenching of the 1G4 and 3H4 states have been attributed to cross-relaxation processes and this phenomena has been analyzed by Inokuti-Hirayama model. The stimulated emission cross-section for the 3F43H6 transition equals to 1.12 × 10−20 cm2 at 1809 nm was calculated using the Füchtbauer-Ladenburg method and compared with the corresponding values of other Tm3+-doped laser hosts. From obtained results, follow that the Tm3+:Y2Te4O11 is a potential candidate for a solid-state laser host operating at 1.8 µm.

Introduction

Among materials contained trivalent lanthanides ions, the Tm3+-doped hosts have been extensively studied due to their potential application in field emission displays (FEDs), scintillators and fiber amplifiers as well as optical sensing [1], [2], [3], [4]. The Tm3+-doped materials have attracted much attention in recent years due to their potential application as laser media operating in the eye-safe spectral range near 2.0 µm. The substantial interest in laser qualities of Tm3+-doped materials is mainly motivated by progress in development of commercial AlGaAs laser diodes which are well suited for optical pumping at around 800 nm into the 3H4 level of Tm3+. In addition, the efficient NIR laser emission corresponds to the 3F43H6 transition of Tm3+ associated with the 1.8–2.0 µm spectrum region may be useful mainly for environmental detecting and medical surgeries [5], [6], [7]. Therefore, laser emission at 1.9 µm has been demonstrated in several Tm3+-doped materials such as fluorides and vanadates crystals as well as tellurite glasses [8], [9], [10].

The research on the rare earth oxotellurates(IV) with general formula RE2Te4O11 has been initiated by Redman and Blasse in the late 60's and the early 70's [11], [12]. Studies on crystal structures of RE2Te4O11 have been carried out only in recent years, however. These results indicate that RE-oxotellurates(IV) may be conveniently examined using optical spectroscopy methods due to several reasons. Firstly, the RE2Te4O11 crystals are isostructural in a series of rare earth elements (except Sc3+ and Pm3+ ions) and contain only one crystallographic site available for the rare earth ions (with C1 point symmetry) [13]. Secondly, quite low phonon energy i.e. 790 cm-1 is attributed for RE-oxotellurates(IV) comparing to phosphates (~ 1200 cm-1), silicates (~ 1100 cm-1) and vanadates (~ 890 cm-1) accordingly, the nonradiative losses can be effectively reduced. Finally, the rare earth oxotellurates (IV) can be readily obtained by means of low-temperature solid state synthesis method (below 800 °C). Furthermore, these materials are characterized by high chemical stability (non-hygroscopic) and good mechanical properties. Therefore, RE2Te4O11 doped with trivalent lanthanides ions could be considered as efficient phosphors and laser materials [14], [15], [16], [17].

To the best of our knowledge, the spectroscopic properties of Tm3+-doped Y2Te4O11 have not been hitherto studied and reported. The aim of the present study was to investigate the optical absorption and emission spectra as well as fluorescence decay curves in the aforementioned host. The Y2-xTmxTe4O11 microcrystalline powders (where x = 0.1, 0.5, 1.0, 2.0 and 5.0 at%) were synthesized by conventional solid state reaction method. The Judd-Ofelt theory has been applied in order to characterize the fundamental fluorescence properties of Tm3+ ions. The radiative transition probabilities (A), branching ratios (β) and radiative lifetimes (τR) of the excited levels of the Tm3+ ion were calculated. Füchtbauer-Ladenburg method was used to estimate the stimulated emission cross-section for the 3F43H6 transition. The influence of the Tm3+ concentration on the luminescence decay time and Tm-Tm energy transfer mechanism has been discussed and studied utilizing the Inokuti-Hirayama model.

Section snippets

Synthesis method

Microcrystalline powders of Y2-xTmxTe4O11 (where x = 0.1, 0.5, 1.0, 2.0 and 5.0 at%) were synthesized by conventional solid state reaction method. The details of the synthesis procedure were presented in Ref. [16]. The starting materials of high purity, Y2O3 (99.999%, Stanford Materials), Tm2O3 (99,999%, Stanford Materials) and TeO2 (99.95%, Sigma Aldrich) were mixed in stoichiometric proportions, thoroughly homogenized over 12 h and pressed into tablets of 20 mm in diameter at 0.5 GPa. The

XRD diffraction pattern

In order to identify the chemical phase of materials under study, the X-ray powder diffraction patterns of Tm3+-doped Y2Te4O11 microcrystalline powders were measured for various concentration of activator (0.1, 0.5, 1.0, 2.0 and 5.0 at%). Fig. 1 shows the representative XRD patterns of Y2Te4O11 activated with 0.1 and 5.0 at% of Tm3+, together with theoretical simulation pattern ICSD#418854 [18]. Other Tm3+-doped samples exhibit similar XRD characteristics, thus their XRD patterns have not been

Summary

Tm3+-doped Y2Te4O11 microcrystalline powders containing various concentration of Tm3+ ions, were synthesized by a conventional solid state reaction method. The absorption spectrum (300 K) has been analyzed within the Judd-Ofelt theory in order to evaluate phenomenological Ωλ (λ = 2, 4, 6) parameters, radiative transition probabilities (A), branching ratios (β) of luminescence and radiative lifetimes (τR) of the Tm3+ excited levels. The fluorescence spectra recorded at different excitation

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