are left at 45 to 50 u00b0 c for 12 hours in a lab oven the dried product appears like soft glass called xerogel after crushing the gel in a glass mortar and pestle a fine powder is collected into a high grade alumina boat and fired at 400 u00b0 c for 2 hours rate of heating is 2 u00b0 min and then 900 to 1000 u00b0 c for 3 to 6 hours with the same rate of heating in a box furnace samples are re fired in a forming gas 5 h 2 95 n 2 at 1000 to 1100 u00b0 c for 2 to 4 hours in a tube furnace the samples are left in the furnace until they cool down to room temperature after cooling these fine phosphor powders are subjected to ultrasonic agitation in water ultrasonic treatment helps to break the clusters into very small particles after washing with water powders are dried at 100 u00b0 c for 6 hours depending upon the required amounts this can be scaled up the emission characteristics of the above phosphor recorded at room temperature exciting with excitation vuv and psd are given in table i the preparation procedure is the same as in example i except 20 4 grams of aluminum isopropoxide is replaced by 26 4 grams.