SCINT 2017 - 14th Int. Conference on Scintillating Materials and their Applications

Influence of gallium content and position on thermally stimulated luminescence of multicomponent (Y,Lu,Gd)3(Ga,Al)5O12:Ce garnets

21 Sept 2017, 10:00

1h

Congress Centre "Le Majestic"

Poster presentation P5_characterization Poster Session 3

Speaker

Vladimir Babin (Institute of Physics, AS CR)

Description

Multicomponent (Y,Lu,Gd)₃(Ga,Al)₅O₁₂:Ce garnets are efficient complex oxide scintillators, whose main advantages are achieved owing to the Ga-induced lowering of the conduction band (CB) bottom resulting in burying of shallow electron traps (see, e.g., review [1]). In this work, the (Y,Lu,Gd)₃Ga_xAl_5-xO₁₂:Ce single crystals with different Ga contents are studied by the photo- and thermally stimulated luminescence, NMR, and ESR methods. The results are compared with the data obtained in [2] for the (Lu,Gd)₃Ga_xAl_5-xO₁₂:Ce epitaxial films.

Under irradiation in the 4f - 5d absorption band of Ce³⁺, electrons can be thermally released from the 5d excited level of Ce³⁺ into the CB, migrate along the CB and be trapped at different traps, thermally released from these traps, and finally recombine with the optically created Ce⁴⁺ centers. As a result, the Ce³⁺-related thermally stimulated luminescence (TSL) appears. In case a TSL glow curve peak appears as a result of an electron release from the 5d₁ level of Ce³⁺ into the CB, the activation energy E_a for the TSL peak creation corresponds to the energy distance between the 5d₁ excited level of Ce³⁺ and the bottom of the CB.

The increasing Ga content is found to result in the decreasing E_a value, increasing TSL intensity, decreasing temperature of the luminescence quenching, low-temperature shift of the TSL peaks and decrease of the corresponding trap depths. It results also in the increasing concentration of Ga³⁺ ions in the octahedral Al³⁺ sites (N_oct) as compared with the tetrahedral ones (N_tetr) [3]. Both in the epitaxial films and single crystals of different composition and origin, having strongly different concentrations of non-compensated vacancies and antisite defects, the E_a dependences on the Ga content practically coincide and are nonlinear (see, e.g., [2]). However, the dependences of the TSL peaks positions, the corresponding trap depths, and the N_oct/N_tetr ratio on the Ga content are close to linear. These data allow us to suggest that in the multicomponent garnets with x>1.4, E_a is not equal to the 5d₁ - CB energy. Most probably, E_a is the energy distance between the 5d₁ level of Ce³⁺ and a defect level located between the 5d₁ level and the CB.

These data indicate that in the multicomponent garnets, Ga can play not only a positive but also a negative role (the appearance of additional defects, reduced activation energies for the photostimulated defects creation and luminescence thermal quenching) which increases with the increasing Ga content.

References

[1] M. Nikl, et al., Prog. in Cryst. Growth Charact. Mater. 59, 47 (2013).

[2] V. Babin, et al., Opt. Mat. 62, 465 (2016).

[3] V. Laguta, et al., J. Phys. Chem. C 120, 24400 (2016).