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Journal of Physical Studies 25(3), Article 3703 [6 pages] (2021)
DOI: https://doi.org/10.30970/jps.25.3703 LUMINESCENCE OF CsPbBr3 MICROCRYSTALS EMBEDDED IN THE KBr MATRIX
M. Dendebera{1}
{1}Ivan Franko National University of Lviv,
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The paper studies the luminescence-kinetic properties of CsPbBr$_{3}$ microcrystals embedded in the KBr matrix. It is shown that embedded CsPbBr$_{3}$ microcrystals are formed during the growth of KBr crystals doped with CsPbBr$_{3}$ (1 mol.{%}). The measurements of spectral-kinetic parameters of the luminescence from embedded microcrystals under the excitation of laser diode ($λ = 405$ nm) were carried out over the temperature range of 12-300 K. The luminescence of embedded CsPbBr$_{3}$ microcrystals reveals narrow bands at 532 (band A) and 536 nm (band B) with luminescence decay times in the nanosecond time range at the liquid nitrogen temperature.
Broadband luminescence peaking at 550 nm can be attributed to recombination luminescence involving low-energy traps with energy less than the exciton binding energy. Electrons released from the traps at temperatures higher than the trap depth energy can recombine with holes to produce exciton emission or interband recombination luminescence. Another possible interpretation of this band is the luminescence of self-trapped excitons, which is discussed in the configuration coordinate model.
The luminescence parameters of CsPbBr$_{3}$ particles embedded in KBr combine the properties characteristic of bulk and nanosized samples. The embedded CsPbBr$_{3}$ particles are characterized by a doublet structure of the near band edge emission, which is a feature of bulk samples. The peaks are attributed to direct transitions at the Г point and indirect ones from the Rashba valleys. The evidence in support of this interpretation may be the temperature dependence of the maxima position of these bands, which follows the trend observed for a single crystal. With an increase in temperature, band A shows a major tendency to shift towards high energies and this behavior can be explained as resulting from the thermal expansion of the matrix. The behavior of band B with an increase in temperature above $\sim$ 120 K is different. Its position shifts to the region of lower energies. This can be explained by the predominant contribution of the electron-phonon interaction in this temperature range and is an indication of the different nature of these near edge bands. In the case of band B, a contribution from the asymmetric oscillations of the lattice causes an increase in the value of the Rashba splitting.
Near band edge luminescence is quenched with an activation energy barrier of 180 meV, which is characteristic of the luminescence of CsPbBr$_{3}$ nanoparticles. The shift of the near band edge luminescence to the region of lower energies in comparison with single crystals is explained by the effect of the hydrostatic pressure from the KBr matrix upon the embedded CsPbBr$_{3}$ particles.
Key words: Rashba effect, free excitons, near edge luminescence, CsPbBr3 embedded microcrystals
