Any person in the unclassified service employed full time by The University of Connecticut, who served prior to his employment by the state in a teaching or administrative position as a hospital pharmacist in a teaching and research hospital affiliated with an educational institution in another state, for which service he has received, or will receive, no retirement benefit or pension, may, subject to the following condition, gain credit for such prior service, not to exceed ten years in the aggregate, on paying to the State Employees Retirement Fund, for each year of such prior service, six per cent of his annual rate of compensation when he first became a full-time employee of this state. Such payment shall be made before July 1, 1966, or within one year of his first full-time employment with the state, whichever is later. When a person who has gained credit for such prior service retires, not more than one year of such out-of-state service may be counted for each two years of state service, provided, if such person has purchased more of such out-of-state service than can be counted, refund of the amount paid on the extra years of service shall be made.