In a method of preparing a storage phosphor layer on a support by vapour deposition from a crucible unit by heating as phosphor precursor raw materials a matrix component and an activator component or a precursor component thereof, wherein said crucible unit comprises at least a bottom and surrounding side walls as a crucible for phosphor precursor raw materials present in said crucible in liquid form, wherein said crucible unit further comprises at least a chimney as part of the crucible unit and a slit allowing phosphor precursor raw materials to escape in vaporised form from said crucible unit in order to deposit it as a phosphor layer onto said support, the step of heating said precursor raw materials in the crucible in liquid form proceeds up to a temperature T1 and the step of heating said precursor raw materials in vaporised form in said chimney, proceeds up to a temperature T2, characterised in that a positive difference in temperature [T2 - T1] is maintained.