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In this paper, Y4GeO8:Bi3+,Eu3+ phosphor with dual emission centers was elaborated via conventional solid‐state reaction technology. Thorough research on the structure, morphology, and luminous properties of Y4GeO8:Bi3+,Eu3+ phosphor, the potential applications in optical thermometry were investigated by means of fluorescence intensity ratio and thermochromic techniques. Under 290 and 347 nm excitation, Y4GeO8:Bi3+,Eu3+ phosphor presents broadband emission from 3P1 → 1S0 transition of Bi3+ ions and characteristic emission peaks from 4f–4f transition of Eu3+ ions. Outstanding temperature‐sensing capabilities are acquired from Y4GeO8:Bi3+,Eu3+ phosphor. The maximum relative sensitivity (Sr) can attain 1.51% K−1 (λex = 290 nm). With temperature raising (303–513 K), the emitted color of Y4GeO8:Bi3+,Eu3+ phosphor (λex = 290 nm) shifts from faint yellow to red with a high chromaticity shift (0.180), which can be distinguished by the unaided eye clearly. Our results indicate that Y4GeO8:Bi3+,Eu3+ phosphor has potential applications in optical temperature measurement and high‐temperature safety marker. [ABSTRACT FROM AUTHOR]

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]

Graphical abstract Highlights • Yb/Er/Eu: Gd 2 Ti 2 O 7 powders are prepared by a simple sol-gel method • Red emission is due to the high CR possibility of 4F 7/2 + 4I 11/2 → 4F 9/2 + 4F 9/2. • Trace amount of Er3+ are used to reduce deleterious CR between Er3+ and Eu3+. • Excitation-dependent multi-color emissions are achieved. • These systems are suitable for anti-counterfeiting application. Abstract Lanthanide ions with abundant energy levels are widely adopted to actualize controllable colorful emissions. Herein, green to red emissions are obtained in Yb/Er: Gd 2 Ti 2 O 7 phosphor by controlling the Er3+ doping content. With further introducing Eu3+ ions, excitation-dependent multi-color emissions are achieved. The related mechanisms are investigated systematically. Our results reveal these systems with bright up- and down- conversion emissions have potential application for anti-counterfeiting. [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]

Near-infrared (NIR) phosphors converted to light-emitting diodes (pc-LED) sources have extensive application prospects in medical imaging, foodstuff analysis and plant growth fields. However, there are some shortcomings in NIR phosphors, such as narrow emission band and poor thermal stability. Here a new wide band NIR luminescent phosphor Cr3+-doped Sr 3 Sc 4 O 9 (SSO) is introduced. The emission spectrum ranges from 600 nm to 1000 nm, with a peak value of 761 nm and the value of full width at half maximum (FWHM) is 120 nm. The internal quantum efficiency (IQE) of sample is about 87% according to the fitting result. The most appropriate doping concentration is x = 0.02 and the best excitation wavelength is 468 nm, which matches the commercial blue chip. At the same time, the phosphor shows good thermal stability in variable temperature spectrum test, and can maintain 70.4% emission intensity at 373 K relative to room temperature. To better understand its practical applications, packaged pc-LED is designed to show good NIR light penetration in spectral penetration tests. This study provides an excellent choice of NIR phosphors. • Sr 3 Sc 4 O 9 :Cr3+ phosphors are promising near-infrared (NIR) emission materials. • The phosphors retain 70.4% of initial emission intensity at 373 K. • The IQE of sample is about 87%. • The pc-LED device can be applied in NIR penetration analysis. [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]