Abstract: In a method of preparing a phosphor or scintillator layer to become deposited on a support, a vapor depositing step is applied from a crucible unit by heating as phosphor precursor raw materials present in said crucible, a Cs(X,X?) matrix compound and an activator or dopant precursor compound, wherein said crucible unit comprises at least a bottom and surrounding side walls as a container for phosphor precursor raw materials present in said crucible in liquefied form after heating said crucible, and wherein said Cs(X,X?) matrix compound has a higher vapor pressure than said activator or dopant precursor compound, said method comprising a step of providing said activator or dopant compound in form of a precursor raw material represented by the formula CsxEuyX?(x+?y), wherein x, y and ? are integers, wherein x/y is more than 0.