Optical spectroscopy of 3d7and 3d8impurity configurations in a wide-gap semiconductor (ZnO:Co,Ni,Cu)

Abstract

Four emission bands have been studied at low temperatures with differently doped ZnO crystals. In the ${\mathrm{Co}}^{2+}$(${\mathrm{d}}^{7}$) ion, two transitions to the $^{4}\mathrm{A}_{2}$(F) ground state give rise to new luminescence bands, viz., starting from the $^{4}\mathrm{T}_{2}$(F) term (around 3600 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) and from the mixed $^{4}\mathrm{T}_{1}$(P)${,}^{2}$${\mathrm{T}}_{1}$(G), $^{2})$ levels (around 15 100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$). Fine-structure and polarization properties of these transitions agree with conclusions on ${C}_{3v}$ and spin-orbit splittings drawn from previous absorption data. An emission of ZnO:Ni near 6000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ is identified as the $^{4}\mathrm{T}_{2}$(F)${\ensuremath{\rightarrow}}^{4}$${\mathrm{A}}_{2}$(F) transition of the ${\mathrm{Ni}}^{3+}$(${\mathrm{d}}^{7}$) ion in a trigonal environment. While the samples display the ${\mathrm{Ni}}^{2+}$(${\mathrm{d}}^{8}$) transmission spectrum, a charge-transfer process leads to a donor-type conversion of the center entailing the transient ${\mathrm{Ni}}^{3+}$ state. A similar mechanism is proposed to explain the emission of ZnO:Cu in the 5600--6900-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ range. Its fine-structure and polarization behavior can be understood in terms of ${T}_{2}$${\mathrm{\ensuremath{-}}}^{3}$${\mathrm{T}}_{2}$(F) \ensuremath{\rightarrow}${\mathrm{A}}_{1}$${\mathrm{\ensuremath{-}}}^{3}$${\mathrm{T}}_{1}$(F) transitions of a ${\mathrm{Cu}}^{3+}$(${\mathrm{d}}^{8}$) ion. Its occurrence is established in a model of one-electron configurations also covering the other known Cu transitions. The excitation spectrum presented is explained by a Tanabe-Sugano type of reasoning for the ${d}^{8}$ excited states which are reached in the ${d}^{9}$\ensuremath{\rightarrow}${d}^{8}$ conversion.

Optical spectroscopy of 3d7and 3d8impurity configurations in a wide-gap semiconductor (ZnO:Co,Ni,Cu)

Citations Over TimeTop 13% of 1987 papers

Abstract

Related Papers