The luminescent phosphor degradation in a cathode ray display tube, caused by aging, is decreased. This decrease is achieved by introducing before and/or during evacuation a hydrolyzable gas into the tube's inner space for a limited time interval, using a partial pressure which is essentially larger than the eventual final vacuum pressure of the cathode ray tube, and then allowing the final vacuum pressure to be achieved without any further supply of gas. Thereafter, the cathode ray tube is sealed in a gastight manner.