Effect of Tm3+ -induced defects on the photoexcitation energy relaxation in Tm-doped Alx Ga1-x N
We provide evidence that the Tm3+ -induced defects in Tm-doped Alx Ga1-x N hosts play a major role in the nonradiative transfer of the excitation energy from the I1 6 state to the D1 2 state of Tm3+ ions from which the most efficient photoluminescence (PL) transition (465 nm) occurs. Once the concentration of the Tm3+ -induced defects decreases with increasing x, the PL transitions starting from the I1 6 state (298, 357, 395, 530, and 785 nm) may be significantly enhanced. It is shown that the indirect excitation of the I1 6 state results from the Auger-type energy transfer due to the nonradiative band-to-band recombinations in the Alx Ga1-x N host of a given x. In contrast, the PL transitions starting from the G1 4 level (479 and 807 nm) can be excited through either an indirect or a direct regime. In both cases the G1 4 level is populated by the radiative relaxation of the higher energy excited states I1 6, P3 0, P3 1, and P3 2 of Tm3+ ions. © 2009 The American Physical Society.
Glinka, YD; Everitt, HO; Lee, DS; Steckl, AJ
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