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A new thermographic nanocrystalline Sr 4 Al 14 O 25 :Mn 4+ ,Tb 3+ phosphor was developed, and the concentrations of both dopants and the synthesis conditions were optimized. The combination of the thermally quenched luminescence from the Mn 4+ ions to the almost temperature-independent emission from Tb 3+ provides a sensitive luminescent thermometer ( S R = 2.8%/°C at 150 °C) with strong emission color variability. In addition, a figure of merit for this luminescence thermochromism was proposed, as the relative sensitivities of the x and y CIE coordinates, which for this phosphor reaches at 150 °C S R ( x ) = 0.6%/°C and S R ( y ) = 0.4%/°C, respectively. Noncontact thermal imaging was demonstrated with this phosphor using a single consumer digital camera and exploiting the ratio of red (R) and green (G) channels of the RGB images, thereby confirming the high application potential of Sr 4 Al 14 O 25 :Mn 4+ ,Tb 3+ nanocrystals for thermal sensing and mapping.