Lateral flow diagnostic device that contains a phosphorescent material encapsulated in a crosslinked polymer matrix

There is provided a lateral flow diagnostic device that employs a phosphorescent particle. The particle includes, for example, an organic phosphorescent material encapsulated in a cross-linked halogen-containing polymeric matrix. The cross-linked halogen-containing polymeric matrix has at least one percent by mass weight of halogen atoms, and the cross-linked halogen-containing polymeric matrix shields the encapsulated phosphorescent material from phosphorescence quenchers.