Optical spectroscopy and energy transfer in amorphous AlN-doped erbium and ytterbium ions for applications in laser cavities

Sputter-deposited thin-film amorphous AlN:Er (1at.%) emits at 554 and 561nm as a result of H11/22→I15/24 and S3/24→I15/24 transitions. AlN:Yb (1at.%) gives a weak emission peak at 966nm as a result of F5/22→F7/22. The codoping of Er and Yb in AlN results in energy transfer from Er+3 to Yb+3 and enhances the Yb+3 emissions by an order of magnitude. Transfer of electrons occurs from the S3/24 state of Er+3 to the F5/22 state of Yb+3. The weak emission from Yb+3, when excited by a 532nm laser in the absence of Er+3, confirms that the luminescence enhancement in ytterbium is due to energy transfer and not to direct green light excitation by the erbium emission. A possibility of population inversion and a four-level laser cavity formation exists in the Er+3–Yb+3 system.