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Rare-earth doped oxysulfides have gained considerable attention as a luminescence host material owing to its good chemical stability and high efficiency. In this study, Er3+-sensitized La2O2S nanoparticles are prepared by the high-temperature co-precipitation method. La2O2S:2%Er3+ is selected to construct La2O2S:Er3+@La2O2S core/shell structures through epitaxial growth, and the luminescence properties are studied. The surface defects of La2O2S:Er3+ are repaired by the inert protective shell, and the luminescence intensity of the core/shell nanocrystals is increased by 9.6 times. Finally, MAPbI3 is spin-coated over the La2O2S:Er3+@La2O2S film to construct narrow band near-infrared photodetectors. Under 1550 nm excitation, the response rate is 23 mA W−1, detection rate is 2.57 × 108 Jones, and response time is 220 ms. [ABSTRACT FROM AUTHOR]

Lanthanide ion-doped up-conversion (UC) luminescent materials are highly coveted for their utility in diverse applications such as anti-counterfeiting, fluorescence labeling, and temperature sensing. Here, we attempt to adopt SrY2S4 as a novel host lattice for UC luminescence and high-sensitive optical thermometry under near-infrared irradiation. The results show that the single Er3+-doped SrY2S4 samples present their main emissions in green and red regions under 1550 and 980 nm excitations, which correspond to the H11/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ions, respectively. The green to red intensity ratio increases with the Er3+ concentration under both 980 and 1550 nm excitations. The mechanisms of UC luminescence and energy transfer are further systematically investigated by UC spectra and fluorescence decay dynamics. Furthermore, the non-contact temperature sensing performance of the SrY2S4:10%Er3+ sample is explored via employing fluorescence intensity ratio (FIR) technology. At an excitation of 980 nm, the maximum absolute sensitivity (SA) reaches 7.5 × 10−3 K−1 at 480 K. By utilizing a much safer excitation laser of 1550 nm, the maximum SA achieves 8.4 × 10−3 K−1 at 450 K, with a high and stable SA of more than 7.9 × 10−3 K−1 over a broad temperature range of 360–570 K. The relative sensitivity is 1.06% and 1.01% K−1 under 980 and 1550 nm excitations, respectively. These results indicate that the ternary sulfide SrY2S4 can be adopted as a novel host to achieve promising UC luminescence and thermal sensing performance. [ABSTRACT FROM AUTHOR]

The development of phosphors with color-tunable luminescence including white emission is at the forefront of lighting and display technologies. Herein, Dy3+,Tm3+ single-doped or co-doped K3Y(PO4)2 phosphors are synthesized through the solid-state reaction method. By properly adjusting the ratio of Dy3+,Tm3+ co-doping concentrations, color-tunable luminescence from blue to yellow, including white luminescence, is realized under 359 nm excitation. The mechanism of energy transfer between Tm3+ and Dy3+ is further investigated via measuring the luminescence decay curve. Based on efficient energy transfer from Tm3+ to Dy3+, the emission of Dy3+ exhibits an abnormal thermal enhancement phenomenon as the temperature increases. The optical thermometry behaviors of various emission combinations for the Dy3+,Tm3+ co-doped system are analyzed. The maximum sensitivity can be obtained as a constant of 4.8 × 10−3 K−1, which is conducive to improve the measurement accuracy of optical temperature sensing at high temperatures. Furthermore, we also demonstrate the applicability of K3Y(PO4)2:Tm3+,Dy3+ phosphors in white LEDs, providing proof-of-concept for the lighting and display fields. [ABSTRACT FROM AUTHOR]

Red up-conversion luminescence with both emission and excitation peaks within the "tissue transparency window" makes for ideal fluorescent labels for deep tissue penetration and low-background biological imaging. In this work, an efficient strategy is proposed to realize bright red up-conversion luminescence based on interfacial energy transfer (IET), and the luminescence centers (Er3+ and Tm3+) and sensitizers (Yb3+) are doped in separate layers to avoid deleterious cross-relaxation. The IET process between Yb3+ and Er3+ can enable bright red photon up-conversion under 980 nm excitation via fine control and manipulation of the lanthanide ion concentration and shell thickness. By appropriately employing the fluorescence intensity ratio technique, an optical thermometer based on non-thermally coupled energy levels demonstrates a superior relative sensitivity of 2.02% K−1 across the whole temperature region. NaYF4:Er3+,Tm3+@NaYF4:Yb3+ with strong red UC luminescence and highly sensitive performance exhibits potential for application in the field of non-contact temperature sensing. [ABSTRACT FROM AUTHOR]

The thermal effects of NaYF4:Er microcrystals under 1550 nm laser diode irradiation were investigated using an infrared thermal imaging method. The results revealed that the temperature of the LD irradiation beam area was non-uniform. The NaYF4:Er sample exhibits a rapid temperature increase within 5–10 s, and the heating process reaches its steady state after 60 s of irradiation when exposed to 1550 nm LD. The response time, temperature increase, and emission intensity of the samples depend on the excitation power density and concentration of doped Er3+ ions. Low excitation power density is required to avoid the influence of thermal effects on the up-conversion emission spectra measurement. Rapid scanning in up-conversion emission spectra measurement is not effective in preventing the heating effect under high excitation power pumping. In addition, a relative deviation of temperature, existing in fluorescence intensity ratio technique, decreased with the increasing irradiation time. [ABSTRACT FROM AUTHOR]

The development of phosphors with color-tunable luminescence including white emission is at the forefront of lighting and display technologies. Herein, Dy 3+ ,Tm 3+ single-doped or co-doped K 3 Y(PO 4 ) 2 phosphors are synthesized through the solid-state reaction method. By properly adjusting the ratio of Dy 3+ ,Tm 3+ co-doping concentrations, color-tunable luminescence from blue to yellow, including white luminescence, is realized under 359 nm excitation. The mechanism of energy transfer between Tm 3+ and Dy 3+ is further investigated via measuring the luminescence decay curve. Based on efficient energy transfer from Tm 3+ to Dy 3+ , the emission of Dy 3+ exhibits an abnormal thermal enhancement phenomenon as the temperature increases. The optical thermometry behaviors of various emission combinations for the Dy 3+ ,Tm 3+ co-doped system are analyzed. The maximum sensitivity can be obtained as a constant of 4.8 × 10 -3 K -1 , which is conducive to improve the measurement accuracy of optical temperature sensing at high temperatures. Furthermore, we also demonstrate the applicability of K 3 Y(PO 4 ) 2 :Tm 3+ ,Dy 3+ phosphors in white LEDs, providing proof-of-concept for the lighting and display fields.

Lanthanide ions have abundant excited-state channels which result in a radiation relaxation process generally accompanied by a non-radiation relaxation process. However, non-radiation relaxation processes will consume the activation energy and reduce the luminescence efficiency of the phosphor. Two lasers with an excitation energy which matched the ground state absorption and excited state absorption of ions were used to excite the phosphors to avoid the non-radiation relaxation process. This approach can achieve the purpose of populating specific states of the lanthanide ions, and furthermore effectively tunes the luminescence intensity and color output of the sample. Results show that the red emission intensity of the sample is significantly improved and this is caused by populating the 4 F 9/2 level under simultaneous 1510 nm and 980 nm excitation. Then when the 1510 nm and 808 nm co-operate to excite the sample, the green emission obtained increased sharply because the 2 H 11/2 / 4 S 3/2 states were efficiently populated. As a proof-of-concept experiment, this new approach has potential in the applications of solar cells., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The thermal effects of NaYF 4 :Er microcrystals under 1550 nm laser diode irradiation were investigated using an infrared thermal imaging method. The results revealed that the temperature of the LD irradiation beam area was non-uniform. The NaYF 4 :Er sample exhibits a rapid temperature increase within 5-10 s, and the heating process reaches its steady state after 60 s of irradiation when exposed to 1550 nm LD. The response time, temperature increase, and emission intensity of the samples depend on the excitation power density and concentration of doped Er 3+ ions. Low excitation power density is required to avoid the influence of thermal effects on the up-conversion emission spectra measurement. Rapid scanning in up-conversion emission spectra measurement is not effective in preventing the heating effect under high excitation power pumping. In addition, a relative deviation of temperature, existing in fluorescence intensity ratio technique, decreased with the increasing irradiation time.