Spectroscopic calculation of NaYF4 contained transparent glass ceramics doped with different content of Nd3+

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Abstract

Transparent oxyfluoride glass ceramics doped with different content of Nd3+ were fabricated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed abundant spherical NaYF4 nano-crystals distributing homogeneously among the glass matrix. The absorption spectra, emission spectra and 4F3/2 level fluorescence decay curves of the precursor glasses and glass ceramics were measured. The considerable blue shifts of absorption peaks and longer lifetime of 4F3/2 level in glass ceramic compared to those in precursor glass indicate the incorporation of Nd3+ into NaYF4 crystallites, which is also confirmed by the Judd–Ofelt calculation. The synchronous variations of the fluorescence lifetime and the quantum efficiency with Nd3+ doping level in glass ceramics indicate the existence of concentration quenching effect, which is considered to originate from the interaction between Nd3+ ions.

Introduction

Since Wang and Ohwaki first reported transparent glass ceramic containing (Pb, Cd)F2 nano-crystals in 1993 [1], the oxyfluoride glass ceramic, fabricated usually through controlled crystallization of a definite fluoride phase in oxide glassy matrix during thermal process, has attracted much attention in the continuous research for the novel photoelectric devices owing to its low phonon energy together with desirable chemical and mechanical stability [2], [3], [4].

NaYF4 is considered to be one of the most efficient upconvension host materials, and rare-earth doped NaYF4 nano-crystals have been found potentially applicable in many fields, such as biology molecular labeling [5] and solar cell [6]. However, NaYF4 bulk crystal is difficult to grow due to the phase transition [7], which restrains its application as bulk material in some fields such as solid-state laser and luminescence device. Therefore, developing transparent glass ceramic containing NaYF4 nano-crystals is of great scientific and technical significance. On the other hand, Nd3+ is one of the high efficient luminescence ions, and its 1.06 μm emission has important application in solid laser. However, compared with other lanthanide ions, there have been only a few works dedicated to the studies on Nd3+-doped transparent glass ceramics [8], [9].

In this work, transparent glass ceramics containing Nd: NaYF4 nano-crystals were prepared. Spectroscopic analyses of the precursor glasses and glass ceramics focusing on 1058 nm emission of Nd3+ were carried out, and the relevant optical parameters were calculated by using Judd–Ofelt theory, which has been used to evaluate the spectroscopic properties of other glass ceramics system successfully [10], [11]. To the best of our knowledge, analogous work on this system has not yet been reported.

Section snippets

Experiments

The glass samples with the compositions (in mol%) of 40SiO2, 25Al2O3, 18Na2CO3, 10YF3, 7NaF–xNdF3 (x = 0.5, 1.0, 2.0, 3.0) were fabricated and named as 0.5G, 1.0G, 2.0G and 3.0G, respectively. The corresponding glass ceramics are named 0.5GC, 1.0GC, 2.0GC, 3.0GC. For each batch, about 15 g raw materials were fully mixed and melted in a covered platinum crucible in air atmosphere at 1450 °C for 1 h, and then cast into copper mold to process quenching. The obtained glasses were annealed at 400 °C

Microstructure

The XRD patterns of the precursor glass and glass ceramic, both doped with 1% Nd3+, are presented in Fig. 1. There are two humps for precursor glass implying its typical amorphous structure. After heat-treatment at 620 °C for 2 h, intense characteristic diffraction peaks of cubic α-NaYF4 emerge. The mean particle size calculated by Scherrer formula based on the peak widths is about 22 nm.

The TEM micrograph of 1.0GC glass ceramic showing abundant spherical NaYF4 nano-crystals with the size of 15–25 

Conclusion

By using Judd–Ofelt theory, some optical parameters of Nd3+ in the transparent glasses and glass ceramics containing NaYF4 nano-crystals have been calculated based on the spectroscopic measurements. The incorporation of Nd3+ ions into NaYF4 induces the prolongation of 4F3/2 level lifetime, which is advantageous to the application of Nd3+ 1.06 μm emission. For glass ceramics, the synchronous variations of the fluorescence lifetime and the quantum efficiency with Nd3+ doping level demonstrates the

Acknowledgments

This work was supported by the National Nature Science Foundation of China (no. 50672098) and the project of Nano-molecular Functional Materials of Fujian Province China (2005HZ01-1).

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