why is potassium dihydrogen arsenate a duller color than potassium nitrate? potassium dihydrogen arsenate has a more stable excited state, so the emitted light is dimmer. potassium dihydrogen arsenate is heavier, so it does not excite as intensely. potassium dihydrogen arsenate also contains arsenic, which is a dull blue color. potassium dihydrogen arsenate is often contaminated with sodium, which dulls the color of light emitted.