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Here, Bi3+, Er3+ co‐activated gadolinium phosphors with multimode emission properties are prepared, which can emits blue, green, and orange light under the excitation of ultraviolet, 980 and 1550 nm, respectively. Moreover, BaGd2O4:Bi3+, Er3+ can show multicolor luminescence under different excitation conditions, such as pump light source, ambient temperature, working current, and other factors. Based on the dynamic luminescence characteristics, the dynamic anti‐counterfeiting experiments are designed based on the phosphor. At the same time, the material also shows multimode temperature sensing characteristics. Under the excitation of 980 nm laser, three strong up‐conversion signals Er3+ ions are generated at 528 nm (2H11/2), 555 nm (4S3/2), and 668 nm (4F9/2), which have different temperature dependences. Based on the fluorescence intensity ratio between thermal‐coupled energy levels (2H11/2/4S3/2) and nonthermal‐coupled energy levels (2H11/2/4F9/2) of Er3+ ions, respectively, the dual‐mode temperature thermometer was constructed with high‐temperature sensitivity. In addition, the fluorescence lifetime of Bi3+ ions also has a strong temperature dependence, which can be used as another temperature detection signal, greatly improving the stability of thermometers under harsh conditions. Therefore, the material has a bright prospect in the field of anti‐counterfeiting and temperature sensing. [ABSTRACT FROM AUTHOR]

Here, La 2 MgGeO 6 : Bi3+, Er3+ samples were synthesized by the high-temperature solid-phase method, and the up/down-conversion luminescence properties were investigated with the excitation of near-infrared light (980 nm and 1550 nm) and ultraviolet light (322–378 nm). Under the excitation of ultraviolet light, the sample can exhibit the characteristic broadband blue emission (Bi3+ ions) and green emission (Er3+ ions). When excited with near-infrared light, the sample has only typical green and orange up-conversion emission bands. The green and orange luminescence could be achieved by adjusting the excitation wavelength. In addition, the sample can present multicolor luminescence with the change of pump power and temperature. At the same time, the temperature measurement performance of the phosphor was explored by using the fluorescence intensity ratio technique based on the Er3+ ion thermal coupling energy level (2H 11/2 /4S 3/2) and non-thermal coupling energy level (2H 11/2 /4F 9/2). The maximum temperature sensitivity reached 1.23 %K−1 and 0.99 %K−1, respectively. Therefore, La 2 MgGeO 6 : Bi3+, Er3+ samples could be candidates for multicolor anti-counterfeiting and temperature sensors material. • La 2 MgGeO 6 : Bi3+, Er3+ phosphors are used as a dual-mode temperature sensor to discuss the TCEL and NTCEL. • The phosphor can not only be used in optical temperature measurement, but also can achieve anti-counterfeit encryption. • Polychromatic luminescence can be realized by changing excitation wavelength, temperature and other conditions. • Using FIR technology to explore the temperature sensing performance, the phosphor is highly sensitive to temperature. [ABSTRACT FROM AUTHOR]

Using a high-temperature solid-phase method, a series of La 2 MgGeO 6 : Bi3+, Eu3+ samples with different doping amounts of Bi3+ and Eu3+ were obtained. The crystal structure, morphology, luminescence characteristics, temperature-varying luminescence spectrum, fluorescence attenuation curve, and energy transfer mechanism of the samples were explored. In La 2 MgGeO 6 : Bi3+, Eu3+ phosphors, Bi3+ and Eu3+ ions occupy the La3+ ion position. Under ultraviolet (UV) excitation, the emission spectra of LMGO: Bi3+ and the excitation spectra of LMGO: Eu3+ have significant spectral overlap, indicating that there is energy transfer between Bi3+ and Eu3+. By adjusting the doping amounts of Eu3+, adjustable luminescence can be obtained in the co-doped samples. According to the varying temperature-dependence trends of Bi3+ and Eu3+ ions, fluorescence intensity ratio technology was used to explore the temperature-sensing characteristics of Bi3+ and Eu3+ ions. The maximum absolute sensitivity and relative sensitivity were 0.074%·K−1 and 2.389%·K−1, respectively. In addition, by monitoring the lifetime decay time of Bi3+ with temperature, the maximum temperature sensitivity of the La 2 MgGeO 6 : Bi3+ samples was 4.09%·K−1. The above results indicate that La 2 MgGeO 6 : Bi3+, Eu3+ samples can be used as potential luminescent materials for temperature detection. • La 2 MgGeO 6 : Bi3+, Eu3+ is explored to be a very promising optical thermometric materials. • The LMGO: Bi3+, Eu3+ shows high signal discriminability in the blue and red regions. • The LMGO: Bi3+, Eu3+ phosphors can circumvent the drawbacks of TCL-based phosphors. • The fluorescence intensity ratio and decay life of the material are highly sensitive to temperature. • The thermal-quenching mechanism of Bi3+ and Eu3+ were discussed. [ABSTRACT FROM AUTHOR]

A series of Ca 2- x Sr x MgSi 2 O 7 : Ce3+, Eu2+ (x = 0, 0.5, 1, 1.5, 2) phosphors were synthesized on the basis of high temperature solid-state reaction strategy. Its phase composition, optical spectral properties, fluorescence lifetime and temperature sensitivity were investigated in detail. Under excitation at 342 nm, the emission spectra of Ca 2 MgSi 2 O 7 : Ce3+, Eu2+ exhibit a purple emission band (Ce3+ ions) and a green emission band (Eu2+ ions). The emission band of Ce3+ overlaps with the excitation band of Eu2+, indicating that there may be energy transfer (ET) between the two ions. The decreasing fluorescence lifetime of Ce3+ with increasing Eu2+ concentration further proves the existent of ET process in Ca 2 MgSi 2 O 7 : Ce3+, Eu2+ phosphor. In addition, Ca 2- x Sr x MgSi 2 O 7 : Ce3+, Eu2+ solid solution was designed and synthesized by Sr2+ substituting Ca2+. As Sr2+ gradually replaced Ca2+, the blue-shift of Ce3+ and Eu2+emission band were caused by the change of crystal field. With the increase of temperature, the fluorescence intensity of Ce3+ and Eu2+ emission bands decreased slowly and rapidly, respectively. Hence, in the Ce3+/Eu2+ co-activated Ca 2- x Sr x MgSi 2 O 7 phosphor, Ce3+ ions and Eu2+ ions can be used as fluorescence intensity ratio (FIR) signals. The maximum relative sensitivity can reach 2.43% K−1 (at 293 K) under 342 nm excitation. The above results indicate that Ca 2- x Sr x MgSi 2 O 7 : Ce3+, Eu2+ phosphors are potential candidates for optical thermometer materials. • The Ca 2- x Sr x MgSi 2 O 7 : Ce3+, Eu2+ (x = 0, 0.5, 1, 1.5, 2) phosphors are promising optical thermometric materials. • The emission peaks of Ce3+ and Eu2+ blue-shift due to the change of crystal field caused by Sr2+ replacing Ca2+. • FIR based on dual luminescence center can overcome the disadvantage of fluorescence intensity ratio based on TCL. • The thermal-quenching mechanism of Ce3+ and Eu2+ were discussed. [ABSTRACT FROM AUTHOR]