Notes/Domino 4 and 5 Forum

i have a field "Closedt" which is actually a date field.By writing the following code:
doc.Date=DateTimeValue 'this will a date-time value but the data type value text format to the Date field
Set Dat = New NotesDateTime(doc.Date(0))
doc.Closedt= Date.dateonly 'this will return the date part only from the date-time value but it will be in text format

the "Closedt" field's data-type has changed to text.
I want a code so that the data type for "Closedt" field will be Date/Time and not Text.