The influence of Pr3+ content on luminescence and optical behavior of TeO2–WO3–PbO–Lu2O3 glass
Graphical abstract
Introduction
In recent years, tellurite glasses doped with lanthanide ions as luminescence centers incorporated into different hosts have attracted much attention due to promising applications in optoelectronics and photonics (see recent review papers [1], [2], [3] and Refs. therein). Tellurite glasses containing, apart from TeO2 also PbO and other oxides, are characterized by a high refractive index (above 2) and a relatively low phonon energy (600–850 cm−1) [4], [5]. Despite of good optical properties, these glasses demonstrate a strong exothermal event during heating that is connected with TeO2 and PbO crystallization [6], [7].
One of the methods to improve the thermal stability of tellurite glasses is addition of lathanide oxides, such as La2O3 or Lu2O3, with the 4f shell of La3+ and Lu3+ ions completely empty and completely filled, respectively, and making these ions optically inactive. Adding La2O3 to the basic TeO2–WO3–PbO glass, an improved glass matrix with the molar composition 60%TeO2–27%WO3–10%PbO–3%La2O3 (TWPLa) has been obtained that appears to be a suitable host for optically active lanthanide ions as demonstrated in our previous works for Nd3+ and Er3+ [8], and Pr3+ ions [9].
Adding Lu2O3 (instead of La2O3) to the basic TeO2–WO3–PbO glass, we have prepared a new matrix with the molar composition 60%TeO2–27%WO3–10%PbO–3%Lu2O3 (TWPLu) and in this work we report on the spectroscopic properties of Pr3+ ions of various concentrations embedded in this host.
The glass transition temperature and resistance of the investigated glasses against crystallization have been determined by performing differential thermal analysis (DTA) measurements.
The absorption- and luminescence spectra as well as radiative decay times of Pr3+ ions in the TWPLu matrix have been analyzed within the standard Judd–Ofelt theory taking into account dispersion of the refractive index obtained from ellipsometric measurements.
Section snippets
Experimental
The host glasses with the molar composition 60%TeO2–27%WO3–10%PbO–3%Lu2O3 (TWPLu) were obtained by melting 16.67 g batches of the high-purity (99.99%) chemicals in gold crucibles in an electric furnace at 850 °C in the air atmosphere. The crucibles were covered with a platinum plate to avoid vaporization losses. Then the melts were poured onto plates preheated to 400 °C, forming a few mm thick layers subsequently annealed in the temperature range 320–340 °C. The density of the TWPLu matrix has been
Thermal properties
Apart from samples from Table 1 we have also studied, for comparison, the thermal behavior of the glass without Lu2O3, i.e. the composition 60%TeO2–30%WO3–10%PbO (TWP), and Fig. 1 shows the DTA curves for all the investigated glasses.
During heating, the studied glasses demonstrate thermal effects characteristic for a typical glassy material and evolution of characteristic temperatures, such as glass transition temperature (Tg) and crystallization temperature (Tcryst), with the glass composition
Conclusions
It has been shown that the TeO2–WO3–PbO–Lu2O3 glass, characterized by high refraction index (n > 2) and sufficient glass stability, can be a suitable host for Pr3+ ions of various concentrations. Applying the standard Judd–Ofelt (J–O) theory to the absorption spectrum of sample TWPLuPr-1, the J–O intensity parameters Ω2, Ω4 and Ω6 have been estimated as being equal to 6.72-, 2.21- and 5.74 × 10−20 cm2, respectively. From photoluminescence (PL) studies it follows that the overall intensity reaches a
Acknowledgment
This work was supported by the Statutory Activities No. 11.11.160.365 (2015) of Faculty of Materials Science and Ceramics, AGH – University of Science and Technology, al. Mickiewicza 30, 30-059 Cracow, Poland.
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