Problem with diacritic characters when exporting data to Excel

[ChrisN]

My app displays a dataset in a GridView and also exports it to Excel.
Characters with diacritical marks (eg umlaut) show up just fine in the
GridView but are mangled when exported to Excel.

Eg

HKS Fördertechnik AG

becomes

HKS Fördertechnik AG

Here's a cut-down version of the export code:

response.Clear()
response.AddHeader("Content-Disposition",
"attachment;filename=" & "InvoiceData.csv")
response.ContentType = "application/vnd.ms-excel"
response.Charset=""
response.Write(ConvertDataViewToString(_exportData)) '
response.End()

Since the data looks okay in the database, and everything is in UNICODE
all the way through to Excel, what am I doing wrong?

Thanks,

Chris N