Re-Excitation of Trivalent Europium Ions Doped into Gallium Nitride Revealed through Photoluminescence under Pulsed Laser Excitation

Abstract

The behavior of trivalent europium (Eu3+) ions doped into gallium nitride (GaN) was investigated under intense excitation conditions to explore the excitation energy transfer characteristics in the presence of large carrier densities. Under such conditions, strong emission from the higher excited 5D1 and 5D2 states of the Eu3+ ions was observed in highly efficient AlGaN/Eu-doped GaN multiple quantum wells grown by organometallic vapor phase epitaxy. This behavior was studied using a variety of excitation sources and conditions. Most notably, when a femtosecond-pulse laser was used, the excitation of the Eu3+ ions into the higher energy states became significant only with a second excitation pulse arriving within the lifetime of the 5D0 state. We propose that an already excited Eu3+ ion is promoted from its 5D0 excited state into the higher 5D J states where it relaxes and can emit from the 5D1 and 5D2 states.

Color-Tunablility in GaN LEDs Based on Atomic Emission Manipulation under Current Injection

“…A low repetition frequency of 100 Hz was used to ensure that re-excitation was minimized. 16 The emission due to the 5 D 0 → 7 F 2 and 5 D 1 → 7 F 1 transitions are shown in Figure 3a and b, respectively. The TR-PL results on the 5 D 0 → 7 F 2 transition exhibit a partial rise that was faster than the temporal resolution of the system, followed by a slow rise, with a rise time of ∼2 μs.…”

“…15 In addition, it was recently demonstrated that the emission spectrum of GaN:Eu could be modified under pulsed laser excitation or current injection. 16 In this report, we demonstrate that it is possible to attain red, green, and blue emission originating from a GaN structure doped with a single type of RE ion, making use of different excited states of Eu 3+ ions and controlling the behavior of the naturally occurring transitions under current injection without the use of additional phosphors or emitting materials. In particular, red to yellow and red to purple color-tunability are demonstrated under constant current injection or by modifying the duty cycle under pulsed current injection.…”

“…Carrier induced de-excitation was shown previously for GaN:Eu and other rare earth ions in semiconductors. 16,36,37 In the case of GaN:Eu, each time the Eu is re-excited, there is a possibility for radiative emission from the 5 D 1 state, which has a much shorter lifetime than the 5 D 0 state. The RY-LED is efficient for this process because the AlGaN barriers increase the carrier concentration in the GaN:Eu layers.…”

“…In regard to the last approach, substantial progress has been made on red GaN-based LEDs by doping the RE element Eu into GaN by organometallic vapor phase epitaxy (OMVPE) . In addition, it was recently demonstrated that the emission spectrum of GaN:Eu could be modified under pulsed laser excitation or current injection . In this report, we demonstrate that it is possible to attain red, green, and blue emission originating from a GaN structure doped with a single type of RE ion, making use of different excited states of Eu 3+ ions and controlling the behavior of the naturally occurring transitions under current injection without the use of additional phosphors or emitting materials.…”

Excitation Efficiency and Limitations of the Luminescence of Eu3+ Ions in GaN

“…During cw optical or electrical excitation, the concentration of free carriers and nearby excited states increases, and enhances the back-transfer, giving rise to a stronger quenching. In particular, an Augertype energy transfer has been shown to effectively de-excite the Eu 3+ ions at high carrier densities 9,12 .…”