A single Er3+ centre in CaGdAlO4:Er3+ has been identified to have C-4v symm
etry from polarized laser selective excitation. This is consistent with iso
valent substitution of the Er3+ ions for host crystal Gd3+ ions. Using both
optical and infrared absorption and polarized laser excited fluorescence,
59 crystal-field energy levels and their wavefunction symmetries have been
identified and used to perform comprehensive single electron crystal-field
analyses for the Er3+ ion centre. For excitation of the F-4(9/2) multiplet,
blue and green upconversion fluorescence is observed. Self-absorption dips
recorded in upconversion excitation spectra are indicative of the presence
of radiative energy transfer processes.