Photoluminescence of Lu3Al5O12:Bi and Y3Al5O12:Bi single crystalline films

Single crystalline films of Lu3Al5O12:Bi and Y3Al5O12:Bi have been studied at 4.2–450 K by the time-resolved luminescence spectroscopy method. Their emission spectrum consists of two types of bands with strongly different characteristics. The ultraviolet band consists of two components, arising from the electronic transitions which correspond to the 3P1 → 1S0 and 3P0 → 1S0 transitions in a free Bi3+ ion. At T < 80 K, mainly the lower-energy component with the decay time ∼10−3 s is observed, arising from the metastable 3P0 level. At T > 150 K, the higher-energy component prevails, arising from the thermally populated emitting 3P1 level. The visible emission spectrum consists of two dominant strongly overlapped broad bands with large Stokes shifts. At 4.2 K, their decay times are ∼10−5 s and ∼10−4 s and decrease with increasing temperature. Both of the visible emission bands are assumed to be of an exciton origin. The lower-energy band is ascribed to an exciton, localized near a single Bi3+ ion. The higher-energy band, showing a stronger intensity dependence on the Bi3+ content, is assumed to arise from an exciton, localized near a dimer Bi3+ center. The structure of the corresponding excited states is considered, and the processes, taking place in these states, are discussed.