Advances in lighting and quantum computing will require new degrees of control over the emission of photons, where localized defects and the quantum confinement of carriers can be utilized. In this contribution, recent developments in the controlled redistribution of energy in rare earth (RE)–doped nanosystems, such as quantum dots or within bulk insulating and semiconducting hosts, will be reviewed. In their trivalent form, RE ions are particularly useful dopants because they retain much of their atomic nature regardless of their environment; however, in systems such as GaN and Si, the electronic states of the RE ions couple strongly to those of the host material by forming nanocomplexes. This coupling facilities fast energy transfer (ET) (<100 ps) and a carrier-mediate energy exchange between the host and the various states of the RE ions, which is mediated by the presence of carriers. A model has been developed using a set of rate equations, which takes into consideration the various ET pathways and the lifetimes of each state within the nanocomplex, which can be used to predict the nature of the emitted photons given an excitation condition. This model will be used to elucidate recent experimental observations in Eu-doped GaN.

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Color tunability from red to orange to yellow has been demonstrated in GaN-based LED devices with Eu-doped GaN layers as the active region. Under current injection, this is achieved by varying the current density and the pulse conditions. The underlying mechanism behind this color tunability is a redistribution of energy among the 5DJ states of a Eu3+ ion. This energy shuffling is facilitated by a local defect that has been neglected in previous modeling work. Including this defect allows for a quantitative prediction of the relative time-averaged populations of the Eu3+ ion's 5D0 and 5D1 states. Extracting, from experimental results, the red and yellow/green emission spectra due to radiative transitions from the respective levels and mixing them allows the overall chromaticity of the emission to be determined for varied excitation conditions. In addition, the model allows us to determine the optimal injection conditions to maximize the gamut of color tunability while minimizing power consumption. These simulations pave the way for practical, systematic color tuning from a single-contact pixel.

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