Hydrostatic pressure induced splitting of recombination luminescence band in KTaO3 : Manifestation of charge transfer vibronic exciton phase

Hydrostatic pressure induced splitting of luminescence transitions under UV photoexcitation was observed in KTaO3 crystal. Two additional satellite bands of recombination luminescence arise at lower and higher energies with approximately the same shift with respect to the initial central band position. After the appearance of satellites at elevated hydrostatic pressures (1.9-6.1 GPa), the luminescence band shape does not exhibit any significant change with further increasing of the applied pressure up to 12.7 GPa. This effect is explained by light-induced occupation of Charge Transfer Vibronic Exciton (CTVE) ferroelectric phase. CTVE-phase occupation increases with hydrostatic pressure up to its proximity to the free CTVE level. Saturated ferroelectric order parameter of this phase splits the recombination luminescence band with two satellites' appearance. Hydrostatic pressure induced satellites in recombination luminescence can be considered as the CTVE-phase manifestation for KTaO3 crystal.