Energy Transfer Between Nanocrystalline Host and Eu[sup 3+] Ions in GaN:Eu[sup 3+] Powders

Abstract

GaN nanocrystalline grains of diameter ϳ8 nm doped by Eu 3+ ions have been synthesized in the powder technology. The energy transfer between nanocrystalline GaN host and Eu 3+ ions has been investigated by photoluminescence excitation spectroscopy. It has been shown that there are three channels for the excitation of Eu 3+ ions: ͑i͒ through quantized states in GaN nanocrystals, ͑ii͒ through defect-related states in the GaN, and ͑iii͒ directly through the excited states of Eu +3 ions. It has been found that for investigated powder the most efficient is the excitation of Eu +3 ions through quantized states in GaN nanocrystals.GaN has recently attracted extensive experimental and theoretical interest mostly due to its wide and direct bandgap. GaN-based materials have been proven quite successful for fabrication of blue and green light emitting devices; however, the realization of red light emitting devices has not been successful due to the difficulties associated with the synthesis processes. An attractive alternative may be the use of rare earth ͑RE͒ ion-doped GaN-based materials. 1 For this reason, a great interest in RE-doped GaN, which combines the electronic properties of GaN with the unique optical properties of RE ions, is observed. It is mostly due to fact that RE ions cover all visible emission ranges with very sharp lines so that their optical characteristics are almost insensitive to the host material and temperature, in contrast to their quantum-well and quantum-dot counterparts. However, the growth of very-high-quality GaN layers is still an expensive and difficult task for research become GaN growth on foreign substrates leads to high dislocations density, which ultimately affects the device performance and its lifetime. Thus, many efforts have been made to obtain high-quality GaN materials doped by RE ions, using typical growth techniques, such as molecular beam epitaxy ͑MBE͒ 2,3 or metallorganic chemical vapor deposition ͑MOCVD͒. 4 The alternative, low cost method for obtaining GaN materials doped by RE ions is the combustion method. 5-8 One of the most interesting advantages of this low-cost technique is the easy way of doping the host material. Moreover, semiconducting nanocrystals are of great interest in optical technology due to the quantum effects which lead to enhanced nonlinear optical properties and change the optical characteristics. It creates the possibility for the new solution in nanotechnology, i.e., matching of the energy structure of the host to the energy levels of the optically active dopant for obtaining more efficient energy transfer and stronger emission. Thus, considerable effort has been directed towards the synthesis of GaN powders as a new kind of synthesizers for doped RE ions, characterized by low absorption coefficients, resulting in their inefficient direct excitation. The deeper understanding of the incorporation of RE dopants into GaN nanocrystals and the excitation mechanisms ͑energy transfer͒ is necessary for optimizing new optoelectronic devices. In this letter pho...

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