in order to be suitable for use in intensifying screen a phosphor should have which of the following characteristics

in order to be suitable for use in intensifying screen a phosphor should have which of the following characteristics?
1. high conversion efficiency
2. high x-ray absorption
3. high atomic number
a. 1 only
b. 3 only
c. 1 and 2 only
d. 1,2 and 3