Daniel R. Gamelin and Hans U. Güdel
Design of Luminescent Inorganic Materials: New Photophysical Processes Studied by Optical Spectroscopy
Acc. Chem. Res. 33, 235-242 (2000)                 

Abstract: Recent spectroscopic results in the emerging area of transition-metal NIR-to-visible upconversion are related. The examples of Ti²⁺-, Re⁴⁺-, and Os⁴⁺-doped materials showing upconversion illustrate GSA/ESA, GSA/ETU, and photon avalanche multiphoton excitation mechanisms, respectively. Strategies for manipulation of such upconversion processes using the spectroscopic or magnetic properties of the host material are described. High-resolution low-temperature continuous-wave absorption and emission and time-resolved emission experiments combine to yield information about energy splittings, intensities, and excited-state dynamics, and assist in the design and development of luminescent materials showing novel multiphoton excitation properties.