Advances in Materials Science and Engineering

Volume 2014 (2014), Article ID 751973, 5 pages

http://dx.doi.org/10.1155/2014/751973

Research Article

Up- and Downconversion Luminescence Properties of Nd³⁺ Ions Doped in Bi₂O₃–BaO–B₂O₃ Glass System

R. Ruamnikhom,¹ P. Limsuwan,¹ M. Horprathum,² N. Chanthima,³ H. J. Kim,⁴ S. Ruengsri,⁵ and J. Kaewkhao³

¹Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand

²Optical Thin-Film Laboratory National Electronics and Computer Technology Center, Pathumthani 12120, Thailand

³Center of Excellence in Glass Technology and Materials Science (CEGM), Nakhon Pathom Rajabhat University, Nakhon Pathom 73000, Thailand

⁴Department of Physics, Kyungpook National University, Deagu 702-701, Republic of Korea

⁵Chemistry Program, Faculty of Science and Technology, Nakhon Pathom Rajabhat University, Nakhon Pathom 73000, Thailand

Received 13 November 2013; Accepted 16 December 2013; Published 28 January 2014

Academic Editor: Luigi Nicolais

Copyright © 2014 R. Ruamnikhom et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Physical, optical, and luminescence properties of Nd³⁺ ions in bismuth barium borate glass system were studied. The glasses prepared by a melt quenching method were doped at various Nd₂O₃ concentrations in compositions (40-x)B₂O₃ : 40Bi₂O₃ : 20BaO : xNd₂O₃ (where x = 0.00, 0.50, 1.00, 1.50, 2.00, and 2.50 in mol%). Luminescence properties of the glasses were studied under two excitations of 585 and 750 nm for downconversion. From both excitations, the results show emission bands in NIR region corresponding to the transitions between ⁴F3/2 → ⁴I9/2 (900 nm), ⁴F3/2 → ⁴I11/2 (1,060 nm), and ⁴F3/2 → 4I13/2 (1,345 nm). The luminescence intensity obtained with 585 nm excitation was stronger than 750 nm, with the strongest NIR emission at 1,060 nm. The upconversion emission spectrum exhibits strong fluorescence bands in the UV region at 394 nm ( nm). The processes are associated with excited state absorption (ESA) from ⁴F3/2 level to ⁴D3/2 level and it is the radiative decay from the ⁴D3/2 to ground levels (⁴D3/2 → ⁴I13/2) which are responsible for the emission at 394 nm.

1. Introduction

The first demonstration of laser action in a neodymium doped glass was done by Snitzer in 1961 and since then considerable progress has been made in evaluating the effects of amorphous host materials on the lasing properties of various rare earth ions. A large variety of laser glasses doped with Nd³⁺ ions have been investigated with the purpose of generating efficient broadband laser emission around 1060 nm [1–3]. Recently, glass-ceramics containing neodymium oxides have been found in applications for several different purposes. First of such application has been Nd₂O₃ in special glasses for halogen lamps to absorb ultraviolet rays, harmful emissions to human. In application as refractory glasses, the glasses containing Nd₂O₃ can have high hardness and excellent chemical durability. Lastly, neodymium contained in glass can be used as a band rejection filter for image display devices, owing to absorption originating in the intertransition within the 4f shell of the Nd³⁺ ion [4, 5].

In addition to the rare-earth ion characteristics, the glass host matrices also play a fundamental role in determining the performance of photonic devices since the stimulated emission characteristics of a trivalent rare-earth ion depend on the surrounding host matrix in which the ions are incorporated. The surrounding ligand field can have a considerable influence on the optical absorption cross-section, stimulated emission cross-section and fluorescence decay, and the quantum efficiency of the system [5]. Bi₂O₃ containing glass possesses higher refractive index and exhibits high optical basicity, large polarizability, and large nonlinear optical susceptibility [6]. It was also reported that glasses containing Bi₂O₃ have been developed for nuclear engineering applications because they accomplish the double task of allowing visibility while absorbing radiations like gamma rays and neutrons [7]. Bi₂O₃ cannot be considered as actual network former due to small field strength of Bi³⁺ ion. However, in the presence of conventional glass-forming cations such as P⁵⁺, Si⁴⁺, and B³⁺ it may have this property [8, 9]. Borate glasses are structurally more intricate as compared to silicate or phosphate glasses due to two types of coordination of boron atoms with oxygen (3 and 4) and the structure of vitreous B₂O₃ consisting of a random network of boroxyl rings and BO₃ triangles connected by B–O–B linkages. In addition, the additional modifier oxide causes a progressive change of some BO₃ triangles to BO₄ tetrahedra, resulting in the formation of various cyclic units including diborate, triborate, tetraborate, or pentaborate groups [9]. The presence of two network forming oxides, the classical B₂O₃ and the conditional Bi₂O₃ glass former, the possible participation in the glass structure of both boron and bismuth ions with more than one stable coordination (and, thus, the presence of several structural units namely, BO₃, BO₄, BiO₃, and BiO₆), the capability of the bismuth polyhedra and of the borate structural groups to form independent interconnected networks [4]. Over the last several years, bismuth barium borate glasses have been also useful for variety of optical applications such as radiation shielding window, gamma rays shielding materials, and scintillation counters [10, 11].

Many literatures have been studied on Bi₂O₃–BaO–B₂O₃ glass system and its related properties [12–16]. However, study on rare earth ion doped to this glass structure and its luminescence properties are very lacking. Only one literature doped with Eu³⁺ has been studied by Egorysheva et al., [17] and good luminescence property was obtained. So, the studies of other rare earth ions doped in this glass are needed. In this present work has been to study the effect of Nd³⁺ content on physical, optical, and luminescence properties from excitations and their responding emission spectra of the glass system. The variety of the emission from Nd³⁺ ions in the glasses system could be potential applications to be developed for various fields such as new light sources, display devices, UV-sensors, and interestingly tunable visible lasers. This work is the first report on luminescence properties of Nd³⁺ on Bi₂O₃–BaO–B₂O₃ glass system.

2. Experimental Detail

2.1. Glass Preparation

The glasses with their chemical compositions (40-x)B₂O₃ : 40Bi₂O₃ : 20BaO : xNd₂O₃ (where x is the mol% of Nd₂O₃ content in the glass systems which varied between 0.0, 0.5, 1.0, 1.5, 2.0, and 2.5) were prepared by the normal melt-quenching technique and the glass compositions in mole percent for different Nd₂O₃ dopings are given in Table 1. For each batch composition, 20 g of homogeneous mixture of starting chemicals was melted in high purity alumina crucibles by an electric furnace at a temperature of 1,100°C for 3 hours. The melts were quenched by pouring into preheated stainless steel molds. The glasses were then annealed at 500°C for about 3 hours to remove thermal strains. Finally, the as-prepared glass samples were cut and then finely polished to a dimension of 1.0 cm × 1.5 cm × 0.3 cm.

Table 1: Chemical compositions of the glass systems prepared in this work.

Nd₂O₃ (mol%)
Glass system

0.00
40.00Bi₂O₃ : 20.00BaO : 40.00B₂O₃

0.50
40.00Bi₂O₃ : 20.00BaO : 39.50B₂O₃ : 0.50Nd₂O₃

1.00
40.00Bi₂O₃ : 20.00BaO : 39.00B₂O₃ : 1.00Nd₂O₃

1.50
40.00Bi₂O₃ : 20.00BaO : 38.50B₂O₃ : 1.50Nd₂O₃

2.00
40.00Bi₂O₃ : 20.00BaO : 38.00B₂O₃ : 2.00Nd₂O₃

2.50
40.00Bi₂O₃ : 20.00BaO : 37.50B₂O₃ : 2.50Nd₂O₃

2.2. Measurements

The density () at room temperature of the glass samples was determined by a method based on Archimedes’ method principle. The weights of the prepared glass samples were measured in air and xylene immersion by using a 4-digit sensitive microbalance (AND, HR-200). The molar volume () was calculated using the relation , where is the total molecular weight of the multicomponent glass system. The optical absorption spectra of the prepared glass samples in the UV-VIS-NIR region from 300 to 1,800 nm were recorded at room temperature using UV-VIS-NIR spectrophotometer (UV-3600, Shimadzu). In the NIR luminescence measurement, the Nd³⁺ doped in glass sample was excited by two wavelengths at 585 and 750 nm. The emission spectra were recorded at room temperature using a Quanta Master 3 luminescence spectrometer from Photon Technology International (PTI). For the upconversion luminescence studies, the Nd³⁺ doped glass samples were excited with a 591 nm wavelength. The emission spectra were recorded at room temperature using a spectrofluorophotometer (Shimadzu RF-5301PC, Japan) with a 150 watts Xenon lamp as a light source.

3. Results and Discussions

3.1. Physical Properties

The density and molar volume of the glasses determined with the described methods are shown in Figure 1. As can be seen from the figure, by adding of Nd₂O₃ into the Bi₂O₃–BaO–B₂O₃ glass network, the density of the glass is increased with the increasing of Nd₂O₃ content. This indicates the increase of the molecular weight by the replacement of B₂O₃ with a heavier Nd₂O₃ oxide in the glass and this as expected increases the density of these glasses. However, the variation of density is nonlinearly increasing with composition of Nd₂O3. This is may be due to different loss rates of Bi₂O₃ at high melting temperature process (melting point of Bi₂O₃ is 817°C [18].) The molar volume of the glass systems, however, shows a decrease trend with increasing of Nd₂O₃ content. The molar volumes of glasses were decreased with increasing of Nd³⁺ ions concentration, reflecting increase compactness of the glass structure with higher concentration of Nd³⁺, that is, the decrease of average atomic separation. The variations of density and molar volume with concentration of Nd₂O₃ are presented in Figure 1.

Figure 1: Density and molar volume of Nd³⁺ doped Bi₂O₃–BaO–B₂O₃ glasses.

3.2. Absorption Spectra

The absorption spectra of Nd³⁺ doped bismuth barium borate glasses in the range of 300–1,800 nm at room temperature are shown in Figure 2. It is clearly observed that the height of the absorption bands increase with the increase of Nd₂O₃ concentration. Seven absorption bands were observed and assigned to transitions from the ⁴I9/2 ground state to ⁴F3/2, ⁴F5/2 + ⁴H9/2, ⁴F7/2 + ⁴S3/2, ⁴F9/2, ²H11/2, ⁴G7/2, and ⁴G9/2 levels [19, 20]. The absorptions in the UV-visible and NIR regions were slightly increased with increasing composition of Nd³⁺ in the glass system.

Figure 2: Ground state absorption spectra of Nd³⁺ ions in Bi₂O₃–BaO–B₂O₃ glasses at room temperature.

3.3. Emission Spectra

3.3.1. Downconversion Spectra

The downconversion emission spectra of Nd³⁺ doped bismuth barium borate glass recorded when excited by 585 and 750 nm wavelengths at room temperature are shown in Figure 3. The emission bands in NIR region were assigned to the corresponding transitions: ⁴F3/2 → ⁴I9/2 (900 nm), ⁴F3/2 → ⁴I11/2 (1,060 nm), and ⁴F3/2 → ⁴I13/2 (1,345 nm) [19, 20]. The emission for the ⁴F3/2 → ⁴I9/2 transition was not observable, probably due to its low intensity. Owing to its importance as a high-power and high-energy laser line, the ⁴F3/2 → ⁴I11/2 (1,060 nm) emission is probably the most thoroughly characterized transition for both glass and crystalline hosts. All the luminescence peaks (900, 1,060, and 1,345 nm) obtained when excited with the 585 nm have been shown with stronger emissions than when excited by the 750 nm wavelength. The luminescence peak intensity was decrease with higher Nd₂O₃ concentration with the strongest NIR emission intensity is at 1,060 nm and then 1,345 and 900 nm respectively.

(a)

(b)

Figure 3: NIR luminescences spectra of Nd³⁺ doped Bi₂O₃–BaO–B₂O₃ glasses show downconversion at room temperature when excited by 585 and 750 nm excitation wavelengths.

3.3.2. Upconversion Spectra

Figure 4 shows upconversion emission spectra of bismuth barium borate glass doped Nd³⁺ ions under 591 nm excitation. The emission spectra exhibit strong fluorescence bands in the UV region at 394 nm. The upconversion process may be associated with the excited state absorption (ESA) from ⁴F3/2 to ⁴D3/2 levels. Figure 5 shows the possible upconversion mechanisms. In the first step, Nd³⁺ in the ground level (⁴I9/2) was excited directly by absorbing the excitation wavelength 591 nm photons to the excited ⁴G5/2 level and then these ions relax nonradiatively to the metastable ⁴F3/2 level. The cross-relaxation process between the ⁴G5/2 and ⁴F3/2 levels causes the population of the ⁴D3/2 level by absorbing a second photon. Finally, the excited Nd³⁺ at ⁴D3/2 state can decay radiatively to ground levels and cause the upconversion emission at 394 nm (⁴D3/2 → ⁴I13/2 or ²P3/2 → ⁴I11/2). Through a nonradiative process Nd³⁺ ions at the ⁴D3/2 level can relax to the lower (²P3/2) levels due to a small energy gap between the two levels. This nonradiative decay has the possibility to cause upconversion emissions from the levels at 467 nm (²P3/2 → ⁴I15/2), but this was not observed in these glass structures.

Figure 4: Upconversion luminescence spectra of Nd³⁺ ions in Bi₂O₃–BaO–B₂O₃ glasses when excited with 591 nm at room temperature.

Figure 5: Energy levels and possible transition pathways of Nd³⁺ ions in Bi₂O₃–BaO–B₂O₃ glasses.

4. Conclusions

The physical and luminescence properties of Nd³⁺ doped B₂O₃–Bi₂O₃–BaO–Nd₂O₃ glasses prepared by a conventional melt-quenching method were studied for Nd₂O₃ compositions. Density of glasses was found to increase with increasing of Nd₂O₃ composition. The behavior of molar volume mainly depends on the density of glasses, but it follows an opposite trend with density. The molar volume of glasses was decreased with increasing of Nd₂O₃ concentration, reflecting more compact of the glass structure. The optical absorption spectra in UV-VIS-NIR region were observed with seven absorption peaks assigned to ⁴I9/2 ground state transition to ⁴F3/2, ⁴F5/2 + ⁴H9/2, ⁴F7/2 + ⁴S3/2, ⁴F9/2, ²H11/2, ⁴G7/2, and ⁴G9/2 levels. Downconversion of Nd³⁺ in the glasses was studied under two excitations at 585 and 750 nm. The result shows luminescence peaks at 900, 1,060, and 1,345 nm. Stronger luminescence peak intensity was observed when excited by 585 nm in comparison to 750 nm excitation wavelength. Upconversion observed with 591 nm excitation showed emission spectra at 394 nm. The mechanisms for the excited state absorption (ESA) were purposed as the possible emission pathways from ⁴D3/2 → ⁴I13/2 or ²P3/2 → ⁴I11/2 transitions. These results showed that the Nd³⁺ doped B₂O₃–Bi₂O₃–BaO glass system can be used in laser or optical devices design.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

P. Limsuwan would like to thank King Mongkut’s University of Technology Thonburi (KMUTT) for partially funding the project under the National Research University. J. Kaewkhao, N. Chanthima, and S. Ruengsri would like to thank National Research Council of Thailand (NRCT) for a partial financial support. R. Ruamnikhom would like to thank Institute for the Promotion of Teaching Science and Technology (IPST) for his Ph.D. grant.

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