Luminescence spectroscopy of excitons and antisite defects in Lu3Al5O12 single crystals and single-crystal films

Abstract

-The nature of the intrinsic luminescence of the lutetium aluminum garnet Lu 3 Al 5 O 12 (LuAG) has been analyzed on the basis of time-resolved spectral kinetic investigations upon excitation of two model objects, LuAG single crystals and single-crystal films, by pulsed X-ray and synchrotron radiations. Due to the differences in the mechanisms and methods of crystallization, these objects are characterized by significantly different concentrations of Lu Al antisite defects. The energy structure of luminescence centers in LuAG single crystals (self-trapped excitons (STEs), excitons localized near antisite defects, and Lu Al antisite defects) has been established. For single-crystal LuAG films, grown by liquid-phase epitaxy from a Pb-containing flux, the energy parameters of the following luminescence centers have been determined: STEs in regular (unperturbed by the presence of antisite defects) sites of the garnet lattice and excitons localized near Pb 2+ ions. The structure of the luminescence centers, related to the background emission of impurity Pb 2+ ions, has also been established in the UV and visible ranges. It is suggested that, in contrast to the two-halide hole self-trapping, a self-trapped state similar to STEs in simple oxides ( Al 2 O 3 , Y 2 O 3 ) is formed in LuAG; this state is formed by self-trapped holes in the form of singly charged O -ions and electrons localized at excited levels of Lu 3+ cations. PACS numbers: 78.55.-m

Time‐resolved spectroscopy of exciton‐related states in single crystals and single crystalline films of Lu3Al5O12 and Lu3Al5O12:Ce

“…Later, the intrinsic luminescence of LuAG SC was studied in Refs. 21–24. The 4.95 eV and 4.36 emission bands observed in these papers were ascribed to the STE and the exciton localized near an antisite ${\rm Lu}_{{\rm Al}}^{{\rm 3 + }} $ ion, respectively, while the 3.7 eV emission, to the recombination luminescence of the antisite ${\rm Lu}_{{\rm Al}}^{{\rm 3 + }} $ defect itself.…”

“…19. As the self‐trapped exciton (STE) emission of SC should be strongly suppressed due to a large content of antisite defects 20–24, both these emission bands were ascribed in Ref. 19 to the radiative decay of an exciton localized near an antisite ${\rm Lu}_{{\rm Al}}^{{\rm 3 + }} $ ion.…”

“…The concentration of antisite defects is strongly suppressed in the single crystalline films (SCF) grown by the liquid phase epitaxy (LPE) method 20, 21. Indeed, in LuAG SCF, the above‐mentioned 4.9 and 3.65 eV emissions are absent, and only the STE emission is observed at 4.95–4.98 eV 21–24. However, at the preparation of LuAG SCF in a Pt crucible with the use of the PbO‐based flux, the Pb and Pt ions can be introduced into the SCF 24, 25.…”

“…Indeed, in LuAG SCF, the above‐mentioned 4.9 and 3.65 eV emissions are absent, and only the STE emission is observed at 4.95–4.98 eV 21–24. However, at the preparation of LuAG SCF in a Pt crucible with the use of the PbO‐based flux, the Pb and Pt ions can be introduced into the SCF 24, 25. The luminescence characteristics of single and dimer Pb 2+ ‐based centers were identified in Refs.…”

Non-resonant X-ray/laser interaction spectroscopy as a method for assessing charge competition, trapping and luminescence efficiency in wide band-gap materials

“…The emission is dominated by the hole-trapping F-centre luminescence at 420 nm, with the main electron trapping centre (of unknown origin) having a distribution of thermal trap depths centred at $1.4 eV [11]. Lu 3 Al 5 O 12 has a bandgap energy of $ 7 eV [12] and was first investigated as a potential scintillator material with excellent characteristics when doped with Pr, by Nikl et al [13]. The Pr defects are introduced in their 3+ charge state, emitting fast luminescence in the range 300-400 nm via the characteristic Pr 3 + 4f5d-4f 2 transition [14].…”