In a method of preparing a storage phosphor panel having a phosphor layer coated onto a dedicate substrate by vapour depositing raw phosphor precursor materials comprising a matrix component,an activator component and/or a combination thereof from one or more crucible unit(s) in a vapour deposition apparatus, wherein said crucible unit comprises a crucible container and a vaporisation chimney; said method comprises the steps of (1)adding said raw phosphor precursor materials to said crucible unit, and (2)vapour depositing a phosphor layer from said raw phosphor precursor materials, wherein vapour depositing proceeds at an increased temperature in the crucible unit, said temperature exceeding the melting temperature of said matrix raw material with more than 70°C; characterised in that an "activator coating weight number" for said phosphor layer reaches a value of at least 7,000; said "activator coating weight number" being defined herein.