Optical spectroscopy and unusual temperature shift of f - f zero-phonon luminescence lines: KTaO3:Er

We present a study of KTaO3:Er (approximate to 0.05%) single crystals based on a multifaceted approach including the use of optical absorption, far-infrared reflectivity, electron paramagnetic resonance, photoluminescence spectra, and ab initio simulations. We describe briefly the fundamental consequences of Er doping, in particular, stiffening of TO1 soft mode of KTaO3. We provide information about energy level structures controlling f - f optical transitions in Er3+, on formation of minor cubic octahedral and major orthorhombic Er3+ centers. It is revealed that the temperature shift of narrow zero-phonon emission lines is strikingly unusual being much larger than that typical for trivalent rare-earth impurities.