Ab initio study of luminescence in Ce-doped Lu 2 SiO 5: The role of oxygen vacancies on emission color and thermal quenching behavior

Yongchao Jia, Anna Miglio, Masayoshi Mikami, Xavier Gonze

Результат исследований: Вклад в журналСтатьярецензирование

18 Цитирования (Scopus)

Аннотация

We study from first principles the luminescence of Lu2SiO5:Ce3+ (LSO:Ce), a scintillator widely used in medical imaging applications, and establish the crucial role of oxygen vacancies (VO) in the generated spectrum. The excitation energy, emission energy, and Stokes shift of its luminescent centers are simulated through a constrained density-functional theory method coupled with a ΔSCF analysis of total energies, and compared with experimental spectra. We show that the high-energy emission band comes from a single Ce-based luminescent center, while the large experimental spread of the low-energy emission band originates from a whole set of different Ce-VO complexes together with the other Ce-based luminescent center. Further, the luminescence thermal quenching behavior is analyzed. The 4f-5d crossover mechanism is found to be very unlikely, with a large crossing energy barrier (Efd) in the one-dimensional model. The alternative mechanism usually considered, namely the electron autoionization, is also shown to be unlikely. In this respect, we introduce a new methodology in which the time-consuming accurate computation of the band gap for such models is bypassed. We emphasize the usually overlooked role of the differing geometry relaxation in the excited neutral electronic state Ce3+,∗ and in the ionized electronic state Ce4+. The results indicate that such electron autoionization cannot explain the thermal stability difference between the high- and low-energy emission bands. Finally, a hole autoionization process is proposed as a plausible alternative. With the already well-established excited-state characterization methodology, the approach to color center identification and thermal quenching analysis proposed here can be applied to other luminescent materials in the presence of intrinsic defects.

Язык оригиналаАнглийский
Номер статьи125202
ЖурналPhysical Review Materials
Том2
Номер выпуска12
DOI
СостояниеОпубликовано - 7 дек. 2018
Опубликовано для внешнего пользованияДа

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