Sellmeier＇s　equations　and　the　equations　for　the　thermal　principal　refractive　index　coefficients　as　a　function　of　wavelength　for　7.5　mol%　Nb:KTP　crystals　are　presented.　Based　on　these　equations,　the　nonlinear　optical　parameters　for　7.5　mol%　Nb:KTP　crystals,　especially　the　angular,　spectral,　and　temperature　acceptance　bandwidths,　are　calculated.　By　comparing　these　results　with　KTP　and　KNbO3　crystals,　7.5　mol%　Nb:KTP　crystals　show　better　performance　than　KNbO3　crystals　in　generating　blue　coherent　light　by　direct　second-harmonic　generation　of　a　semiconductor　diode　laser.