A data storage cartridge for a data storage disk drive has a marker including a latent illuminance material such as phosphor. A matte material on the cartridge or within the marker diffusely reflects charging light that is not absorbed by the latent illuminance material in the marker. This reduces noise and signal pollution in the light then emitted by the latent illuminance material. Accordingly, an accurate decay time can be determined. The decay time is checked to provide identification of different types or generations of data storage cartridges or provides a secure keying mechanism for authorized access to proprietary software.