Photoluminescence ͑PL͒ excitation spectroscopy mapped the photoexcitation wavelength dependence of the red luminescence ͑ 5 D 0 → 7 F 2 ͒ from GaN:Eu. Time-resolved PL measurements revealed that for excitation at the GaN bound exciton energy, the decay transients are almost temperature insensitive between 86 K and 300 K, indicating an efficient energy transfer process. However, for excitation energies above or below the GaN bound exciton energy, the decaying luminescence indicates excitation wavelength-and temperature-dependent energy transfer influenced by intrinsic and Eu 3+ -related defects. Native and rare earth-induced defects participate in the energy transfer processes that lead to red light emission in GaN:Eu. 6 An impurity band spreading 370 meV below the conduction band of GaN:Eu has been observed to arise from such defects. 7 Previous measurements of the extended x-ray absorption fine structure show that Er 3+ and Eu 3+ dopants assume a substitutional Ga site with C 3 symmetry. 8,9 Sharp, otherwise forbidden 4f emission lines from Eu 3+ are allowed by symmetry breaking in the GaN host. Nyein et al. recently performed time-resolved photoluminescence ͑PL͒ studies of these emission lines by using both above-and below-band gap excitation. 10 Photoluminescence excitation ͑PLE͒ spectroscopy indicated the impurity band is involved in the energy transfer between the GaN host and the Eu 3+ dopants. In this paper, visible and UV wavelength PLE measurements of GaN:Eu evaluate the excitation wavelength-dependent energy transfer between the GaN host or defects and the Eu 3+ dopants, while temperature-dependent, time-resolved PL ͑TRPL͒ measurements investigate energy transfer and carrier relaxation dynamics.A Eu-doped GaN film was deposited on a p-Si ͑111͒ substrate by solid-source MBE. A thin GaN buffer layer was first deposited at a substrate temperature of 600°C before the main growth took place at 800°C for about 2 h. Details of the growth conditions can be found elsewhere. 4 The Eu cell temperature was 400°C, resulting in a Eu concentration of 8.8ϫ 10 20 cm -3 ͑1 at. % ͒ estimated by secondary ion mass spectrometry. The thickness of the GaN:Eu layer is approximately 2.4 µm. PL spectra were excited by a He-Cd laser ͑E p = 3.815 eV͒, and the tunable light source for PLE spectroscopy was a xenon arc lamp dispersed through an Acton 150 mm monochromator. The luminescence was analyzed by a 0.75 m focal length SPEX single grating monochromator and detected by a thermoelectrically cooled photomultiplier tube ͑Hamamatsu R928͒. Standard lock-in techniques were used for collecting both PL and PLE signals. The pulsed laser source for TRPL measurements was an optical parametric amplifier ͑OPA͒, pumped by a 1 kHz regenerative amplifier seeded by an 80 MHz Ti:sapphire oscillator operating at 800 nm. In this experiment the OPA was tuned between E p = 3.02-4.14 eV while maintaining a pulse intensity of 600 J/cm 2 and pulse width less than 200 fs. The luminescence from the GaN:Eu sample was collected by two UV lenses, spectrall...
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