High energy resolution scintillators having high light output

A method of operation of a detector element comprising:

• transmitting radiation through an object;
• receiving the radiation by a scintillator material to produce photons which are characteristic of the radiation, wherein the scintillator material comprises:
• a matrix material comprising:
• an alkaline earth metal;
• a rare earth element halide, wherein the rare earth element halide comprises at least one rare earth element and at least one halide ion, wherein the halide ion comprises chlorine and bromine, or bromine and iodine, or chlorine and iodine, or chlorine and bromine and iodine;
• an activator ion for the matrix material;
• and detecting the photons by a photon detector optically coupled to the scintillator material and configured to convert the photons into electrical signals, wherein the activator ion comprises cerium and bismuth, or bismuth and praseodymium, or cerium and bismuth and praseodymium.