6. In the complex plane, the points corresponding to the complex numbers $z_{1}, z_{2}, z_{3}$ are $Z_{1}, Z_{2}, Z_{3}$, respectively. If
$$
\left|z_{1}\right|=\left|z_{2}\right|=\sqrt{2}, \overrightarrow{O Z_{1}} \cdot \overrightarrow{O Z_{2}}=0,\left|z_{1}+z_{2}-z_{3}\right|=2 \text {, }
$$

then the range of $\left|z_{3}\right|$ is $\qquad$
6. $[0,4]$.

From the problem, we know that points $Z_{1}$ and $Z_{2}$ lie on a circle centered at the origin with a radius of $\sqrt{2}$.

Without loss of generality, let $Z_{1}(\sqrt{2}, 0)$ and $Z_{2}(0, \sqrt{2})$. Then the coordinates of the point corresponding to $z_{1}+z_{2}$ are $Z(\sqrt{2}, \sqrt{2})$.

Notice that, the geometric meaning of $\left|z_{1}+z_{2}-z_{3}\right|=2$ is the set of points in the complex plane that are 2 units away from point $Z$.
By combining geometric and numerical analysis, we know that the range of $\left|z_{3}\right|$ is $[0,4]$.