To cite the 'immer' package in publications use:

  Robitzsch, A., & Steinfeld, J. (2018). Item response models for human
  ratings: Overview, estimation methods, and implementation in R.
  Psychological Test and Assessment Modeling, 60(1), 101-139.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Item response models for human ratings: {O}verview, 
estimation methods, and implementation in {R}},
    author = {Alexander Robitzsch and Jan Steinfeld},
    journal = {Psychological Test and Assessment Modeling},
    year = {2018},
    volume = {60},
    number = {1},
    pages = {101--139},
  }

  Robitzsch, A., & Steinfeld, J. (2024).  immer: Item response models
  for multiple ratings. R package version 1.6-1.
  https://CRAN.R-project.org/package=immer

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {immer: Item response models for multiple ratings},
    author = {Alexander Robitzsch and Jan Steinfeld},
    year = {2024},
    note = {R package version 1.6-1},
    url = {https://CRAN.R-project.org/package=immer},
  }