Using metallorganic vapor-phase epitaxy, thin films of gallium nitride activated by Eu 3+ ͑GaN:Eu 3+ ͒ have been deposited on sapphire substrates at atmospheric pressure. Luminescence from Eu 3+ ions in GaN has been investigated using photoluminescence ͑PL͒ and PL excitation spectroscopy. Experimental results show that Eu 3+ ions are excited via energy transfer from the host. Analyses of the observed emission and excitation spectra indicate occupancy of multiple sites in the nitride lattice. Using a pulsed laser source, variation of emission intensity with increasing excitation intensity has also been examined. The possibility of emission saturation at high excitation intensity is discussed from the perspective of application in light-emitting diode sources.

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Using a three‐step solution method, we have successfully synthesized rare‐earth (RE) activated AlN, GaN, and pure GaAlN powders. Aluminium and/or gallium nitrates are first dissolved in water. For AlN:RE, rare‐earth nitrates converted from their corresponding oxides of Dy3+ and Tm3+ are then added to the precursor nitrate solution. The mixture is subsequently converted into Al(OH)3:RE by combining with aqueous NH4OH at room temperature. The product is then mixed with aqueous NH4F to form (NH4)3AlF6:RE. The conversion process is complete when the hexafluoride compound is flushed with anhydrous ammonia to produce the final nitride product AlN:Dy3+,Tm3+. GaN, GaN:Tb3+ and GaAlN are synthesized similarly. Single phase, pure GaN and GaAlN formation has been confirmed. Dysprosium oxide has been observed in AlN:Dy3+, Tm3+. Oxygen concentration of approximately 4 at% has been measured in GaN powders, and is slightly higher in AlN powders. Spectroscopic measurements show clearly observable emission from Dy3+ and Tm3+ co‐activated AlN samples. In activated GaN samples, Tb3+ emission has been observed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Due to the recent commercial interest in nitride-based optoelectronics and rare-earth emission in nitride materials, the structural and optical characteristics of GaN:Tb 3+ powders and thin films have been investigated in this work. The powder samples were made using a three-step solution method. Pulsed laser deposition ͑PLD͒ and metallorganic vapor phase epitaxy ͑MOVPE͒ methods were utilized for depositing GaN:Tb 3+ films on sapphire substrates. The GaN powders with activator concentrations up to 8 atom % exhibited Tb 3+ luminescence due to the 5 D 3,4 → 7 F j transitions under cathodoluminescence ͑CL͒ as well as under 243 nm photon excitation. Both near-band-edge emission and activator emission have been observed in PLD thin films made from the corresponding GaN:Tb 3+ powders. X-ray diffraction revealed polycrystalline PLD thin films with a preferred growth direction along the c axis, while scanning electron micrographs showed rough film morphology with submicrometer particles. CL emission from Tb 3+ accompanied by near-band-edge emission and defect emissions from the GaN host was observed for the MOVPE films made using tris͑2,2,6,6-tetramethyl-3,5-heptanedionato͒terbium but not films made with tris͑isopropylcyclopentadienyl͒terbium. Despite visible luminescence from Tb 3+ in GaN powders and thin films, no energy transfer from the host to activator ions was observed. This suggests that Tb 3+ is unlikely to fluoresce if used in a GaN-based optoelectronic device.