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.

The development of efficient electrically driven color-tunable solid-state light sources will enable new capabilities in lighting and display technologies. Although alternative light sources such as organic light emitting diodes (O-LEDs) have recently gained prominence, GaN-based LEDs remain the most efficient light sources available, making GaN the ideal platform for color-tunable devices. In its trivalent form, Europium is well-known for its red emission at ∼620 nm; however, transitions at ∼590 and ∼545 nm are also possible if additional excited states are exploited. Using intentional codoping and energy-transfer engineering, we show that it is possible to attain all three primary colors due to an emission originating from two different excited states of the same Eu3+ ion mixed with near band edge emission from GaN centered at ∼430 nm. The intensity ratios of these transitions can be controlled by choosing the current injection conditions, such as injection current density and duty cycle under pulsed current injection.

No abstract

No abstract