Fitting a function to data

Hello all,

I got the following function:

function y=decay(t,C1,C2,n,t1,t2)

y=C1+(C2-C1)*exp(-n*(t-t1));

itu=find(t<t1 | t>t2);

y(itu)=NaN;

I want to fit this curve on data that I obtained using matlab. However I don't succeed in using the optimization toolbox. Furthermore I don't think it is possible to use the curve fitting toolbox for this. Can anyone help me with this issue?

Kind regards, Rob