Hi, if you won't to use K2Cr2O7, just keep samples at 4 °C for two weeks and they will sporulate naturally.

There are alternatives, but not good ones. As Aissa said, you might get sporulation at 4 C, but at the same time, bacteria and fungi grow and may eliminate your samples. One place to look for alternatives to potassium dichromate is one of our papers (Upton et al., 1986).

Upton, S.J.; Bristol, J.R.; Gardner, S.L.; Duszynski, D.W. 1986. Eimeria halleri sp. n. (Apicomplexa: Eimeriidae) from the Round Stingray, Urolophus halleri (Rajiformes: Dasyatidae). Proceedings of the Helminthological Society of Washington 53: 110-112.

we can use chromium oxide and chromium nitrate

You can use Chlorhexidine Gluconate Solution