Energy transfer in Sm3+:Eu3+ system in zinc sodium phosphate glasses
Introduction
Rare earth ions find wide applications in sensitising solid state and glass lasers, infrared quantum counters as well as infrared to visible converters. Energy transfer between ions in solids can be accomplished either radiatively or nonradiatively and the mechanism and kinetics involved have been extensively addressed [1], [2]. Many workers have treated the radiative and nonradiative transitions in the rare earth ions and succeeded in realising energy transfer process in doubly doped crystals and glasses [3], [4], [5], [6]. In particular, the excellent work by Blasse and coworkers has resulted in the elucidation of energy transfer, energy migration and concentration quenching in various rare earth ions [7], [8], [9], [10].
One important consequence of the energy transfer process is the phenomenon of sensitised luminescence in solids. It is an important factor in increasing the laser efficiency of the materials. Hence this phenomenon has a significant application in the research and development of new laser materials and it is possible to remarkably reduce the threshold energy of laser oscillation in these materials. A large number of studies on sensitised luminescence or fluorescence and concentration quenching have been made, since the wide spread interest results from the breadth of research areas encompassed by the phenomena of energy transfer [11], [12]. In this context samarium possesses a relative range of absorption among rare earth ions and hence in particular, it is a good candidate for sensitising Eu3+. To enhance the europium emission, many workers have sensitised it by rare earth ions and other ions in different matrices [2], [13]. Reisfeld [14], [15] observed energy transfer from UO2+, Bi3+ and Sm3+ to Eu3+ in glasses and found it to be nonradiative with two orders of magnitude enhancement in Eu3+ emission. Keeping in view of the above interesting results, in the present work a quantitative evaluation of the nonradiative energy transfer in the Sm3+:Eu3+ system in zinc sodium phosphate glass has been undertaken.
Section snippets
Experimental
The glasses were prepared using BDH 99.9% purity sodium dihydrogen phosphate and zinc oxide. Samarium and europium oxide of 99.9% purity from Indian Rare Earth Chemicals Ltd. were used as the dopants. Here samarium and europium as dopants in the glasses act as sensitiser and activator respectively. Incorporation of zinc oxide reduces the hygroscopy of the sodium phosphate glasses [16]. Glasses were prepared with the following rare earth combinations.
- I.
0.5, 1, 1.5, 2, 2.5 wt.% of samarium.
- II.
0.5, 1,
Results and discussion
The fluorescence spectrum of Sm3+ and Eu3+ in zinc phosphate glass is shown in Fig. 1(a) and (b) respectively. The band assignments for the various emission transitions have been done by invoking the energy level diagram of Eu3+ and Sm3+ shown in Fig. 2. In the case of samarium the fluorescence measured consists of the emission from the 4G5/2 level to the ground state 6H multiplet, and for europium the observed emission consists of transitions from 5D0 to 7F multiplet. The emission peaks
Conclusion
The fluorescence spectra of the prepared glass systems exhibit emissions from the 4G5/2 level to the 6H multiplet of samarium and 5D0 level to 7F multiplet of europium. The excitation spectra revealed the additional bands for Sm3+ with high oscillator strengths and the occurrence of energy transfer when co-doped with Eu3+ ions. The change of the emission intensities caused by the co-existence of Sm3+ and Eu3+ and the decay time of Sm3+ have been measured. On the basis of the analysis of the
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