Fluorescent light source device and production process of same

A fluorescent light source device comprising a fluorescent plate which has a fluorescent light-emitting layer formed of a polycrystalline material and in which a periodic structure body is formed on an excitation light incident side of the fluorescent light-emitting layer, wherein

• the fluorescent plate has a thermal diffusion layer which is directly bonded to a front surface of the fluorescent light-emitting layer on the excitation light incident side and has a thermal conductivity larger than that of the fluorescent light-emitting layer, and a high thermal conductive layer provided on a back surface of the fluorescent light-emitting layer opposite to the excitation light incident side,
• the high thermal conductive layer is formed of a light reflection layer and a bonding layer made of a metal,
• the fluorescent plate is provided so as to cover a part of a surface of a heat dissipation substrate disposed on a side of the high thermal conductive layer,
• a material for forming the fluorescent light-emitting layer and a material for forming the thermal diffusion layer contain Al2O3, and a difference in coefficient of linear thermal expansion between the material for forming the fluorescent light-emitting layer and the material for forming the thermal diffusion layer is not more than 1×10−6/K,
• the fluorescent light-emitting layer has an exposed area ratio of Al2O3 of not less than 50% in a bonding surface with the thermal diffusion layer and wherein the light reflection layer is made of silver and the thermal conductivity of the material for forming the bonding layer is 40 to 60 W/(m·K).