Near-UV excited multifunctional near-infrared phosphors for anti-counterfeiting and ratiometric thermometer applications

Abstract

Considerable efforts have been devoted to the development of visible light-emitting phosphors for anti-counterfeiting application, but the design of multifunctional near-infrared materials with suitable luminescent properties was lacking. Based on the crystal field theory, a near ultraviolet excitable and near-infrared emitting Ca₂Sn_2(1−x)Al_2(1−x)O₉:2xCr³⁺,2xSi⁴⁺ phosphor was designed. On the one hand, the Ca₂Sn_2(1−x)Al_2(1−x)O₉:2xCr³⁺,2xSi⁴⁺ phosphor showed great potential for applications including anti-counterfeiting and secret signals under a 405 nm near UV laser. The integrated intensity at 150 °C was 75.9%, implying high thermal stability when irradiated with a high power light source. On the other hand, an unexpected red emission component originating from the Cr³⁺–Cr³⁺ dimer was observed and was confirmed by fast luminescence decay and electron spin resonance signals. The different thermal stabilities of Cr³⁺ near-infrared and Cr³⁺–Cr³⁺ red emissions opened up a new opportunity for luminescence ratiometric thermometers.