To cite diffIRT in publications use:

Dylan Molenaar, Francis Tuerlinckx, Han L. J. van der Maas (2015). Fitting Diffusion Item Response Theory Models for Responses and Response Times Using the R Package diffIRT. Journal of Statistical Software, 66(4), 1-34. URL http://www.jstatsoft.org/v66/i04/.

Corresponding BibTeX entry:

  @Article{,
    title = {Fitting Diffusion Item Response Theory Models for
      Responses and Response Times Using the {R} Package {diffIRT}},
    author = {Dylan Molenaar and Francis Tuerlinckx and Han L. J. {van
      der Maas}},
    journal = {Journal of Statistical Software},
    year = {2015},
    volume = {66},
    number = {4},
    pages = {1--34},
    url = {http://www.jstatsoft.org/v66/i04/},
  }