  Hybrid organic-inorganic perovskites (HOIPs) have emerged to the forefront of
optoelectronic materials advancement in the past few years. Due to the nature
of organic compounds within the perovskite structure, its optoelectronic
properties are affected by complex interaction and correlation effects between
the organic and inorganic ions. Using spectroscopic ellipsometry, we observe
two broad plasmonic excitation from the calculated loss function (LF)
-Im[\varepislon^{-1} (\omega)], peak A' and B' at 3.28 eV and 4.26 eV,
respectively.The presence of these two asymmetric peaks in the spectroscopic
ellipsometry (SE) spectra indicates the existence of unconventional plasmons at
room temperature. This is inferred due to the absence of the zero-crossing in
the real part of dielectric function \varepsilon_1 (\omega). Through combined
Near-Edge X-ray Absorption Fine Structure (NEXAFS) and Resonant Photoemission
Spectroscopies (ResPES), we observe resonance enhancement peak close to 15 eV
in the C K-edge region that unravels a charge transfer event due to the opening
of an extra autoionization channel. Additionally, photoluminescence (PL)
spectrum confirms the presence of broadband emission originating from the
self-trapped emission excitons at 2.38 eV due to the soft 2D-HOIPs crystal
structure. We believe that these phenomena directly impact the correlation
strength in 2D-HOIPs. Our results have confirmed the existence of
unconventional plasmons of 2D-HOIPs at room temperature. Such studies in the
emission and plasmonic behavior of perovskites will pave the way for the
efficient light emitting devices or lasers with minimal integrations of the
materials.
