Energy transfer upconversion

ETU(Energy transfer upconversion)

- Energy is transferred from one laser-active ion to another, leading to the excitation of the latter to a higher energy state than what would be achieved through simple photon absorption.

- Primarily facilitated by dipole-dipole interactions b/w ions within the crystal lattie. ETU can significantly influence the optical properties and fluorescence behavior of the material, often contributing to its luminescence characteristics

* ETU: energy transfer b/w two ions, one ion in an excited state transfers its energy to another ion, causing latter to be excited to a higher energy state. Generally nonradiative and can lead to heating of the medium if energy transfer is inefficient

* Auger upconversion: occurs when excited ion transfer energy to another ion, but energy is used to promote an electron to a higher energy level within the same ion, resulting in a nonradiative decay. This process effectively reduces the population of excited states and can lead to increased thermal losses in the system