RESUMO
Mechanoluminescence (ML) materials with tunable emissions can serve in many practical applications; however, their underlying mechanism still needs further clarification. Herein, we developed Eu2+-/Mn2+-/Ce3+-activated Mg3Ca3(PO4)4 (MCP) phosphors and studied their luminescence properties by device fabrication. The intense blue ML is obtained by fabricating MCP:Eu2+ into the polydimethylsiloxane elastomer matrix. The red ML of relatively weak intensity is received in Mn2+ activator, but the ML for the Ce3+ dopant is nearly quenched in the same host. The possible reason is proposed from the analysis of the relative positions between the excitation state and conduction band, together with the trap types. The appropriate location of the excited energy levels in the band gap allows for a larger probability of efficient ML when shallow traps near the excitation states are created synchronously as an effective energy transfer (ET) channel. The concentration-dependent ML for the MCP:Eu2+,Mn2+-based devices indicates that the emitting light color can be tailored, where several ET processes among oxygen vacancies, Eu2+, Ce3+, and Mn2+, occur. The luminescence manipulation with dopants and excitation sources demonstrates the potential applications in visualized multimode anticounterfeiting. These findings open up many possibilities for constructing new ML materials by introducing appropriate traps into the band structures.
RESUMO
The Yb3+-Er3+ and Yb3+-Ho3+ co-doped Y6WO12 (YWO) luminescent materials were synthesized successfully using the solid-state reaction method, and their phase purity, upconversion (UC) spectra, and optical temperature sensing properties were studied. Upon 980 nm excitation, the dominant emission peak around 660 nm is found in the YWO:Yb3+,Er3+ sample, which could be attributed to the Er3+F49/2-I415/2 electronic transition. Two green emission peaks of Er3+ appear in the range from 515-575 nm. For the YWO:Yb3+,Ho3+ phosphor, there are three emission peaks found at 548, 667, and 758 nm, which can be ascribed to the (F45,S52)-I58, F55-I58, and (F45,S52)-I57 transitions of Ho3+, respectively. By studying the emission intensity dependence of the pumping power, the result suggests that the two-photon process is involved for all the above emissions. In the temperature range of 293-553 K, the temperature sensing behavior of the typical YWO:10%Yb3+,1%Er3+ and YWO:10%Yb3+,1%Ho3+ phosphors was investigated in detail, and the results have been shown by using the fluorescence intensity ratio technique and decay curves. The above investigations indicate that the present UC phosphors could be promising phosphor materials for temperature sensor.
RESUMO
Rare earth ion doped luminescent materials are considered potential candidates with a wide range of applications because of their unique optical characteristics. In this work, single-phase Yb3+-Er3+ and Yb3+-Tm3+ co-doped La1.55SiO4.33 (LS) phosphors of a hexagonal system for optical thermometers are reported. Three characteristic emissions of Er3+ were observed at 521, 553 and 659 nm in the LS:Yb3+,Er3+ phosphors under 980 nm excitation, which are assigned to the 2H11/2 â 4I15/2, 4S3/2 â 4I15/2 and 4F9/2 â 4I15/2 transitions, respectively. In the LS:Yb3+,Tm3+ phosphors, one can find two strong emissions at 474 and 790 nm and two weak emissions at 648 and 685 nm. Their upconversion (UC) luminescence mechanisms were studied from their pump-power-dependent spectra. When the samples were measured at various temperatures, their spectral features revealed that different fluorescence intensity ratio (FIR) strategies can be used to characterize their optical temperature-sensing behaviors. The sensor sensitivities were determined from the temperature-dependent UC emission spectra using thermally coupled energy levels (TCELs) and non-TCELs, which had improved compared with those of some other reported optical temperature-sensing luminescent materials. The device fabrication indicated that the developed UC phosphors are promising for applications in optical thermometers.
RESUMO
A series of novel La9.31Si6.24O26:Er3+,Yb3+ (LS:Er3+,Yb3+) luminescent materials have been successfully synthesized by conventional solid-state reaction method. The phases, morphologies and upconversion (UC) luminescence properties were systematically researched by XRD, SEM, PL spectra, etc. The optimum Yb3+ concentration in LS:1%Er3+,xYb3+ was determined to be × = 15%, above which the concentration quenching effect appeared due to the increasing energy back transfer from Er3+ to Yb3+. Meanwhile, the FIR technique (by using I522/I554 and I660/I522 of Er3+) was employed to study the temperature-sensing performance. As the rise of temperature for all the different Yb3+ concentrations, the values of the absolute sensitivity SA increased first and then decreased by utilizing I522/I554, but showed continuous decrease by using I660/I522. For the relative sensitivity SR, it has been found that the SR values for all the samples exhibited gradual decrease with rising temperature. Besides, the experiment of the heating-cooling cycles between 283 and 523 K proved that the LS:Er3+,Yb3+ material has good reversibility and repeatability. The above results indicated that the LS:Er3+,Yb3+ may be a potential candidate for optical temperature sensor.
RESUMO
A series of Ca5.93-m-x-2ySrmBa(PO4)4O:xEu2+,yCe3+,yLi+ (0 ≤ m ≤ 0.5, 0 ≤ x ≤ 0.07, 0 ≤ y ≤ 0.05) phosphors were designed via solid-state reaction method, and the photoluminescence properties were studied for application in white light-emitting diodes (LEDs). When a small amount of Sr2+ was introduced into the initial Ca6Ba(PO4)4O host, the solid solution was formed, which was verified by the XRD technique. The Eu2+ in the host shows intense yellow emitting light, which can be largely enhanced by incorporating Sr2+ in the host. When the Ce3+ was doped into the host, blue emission was received under 380 nm excitation, and the optimal Ce3+ concentration is for y = 0.04. Very efficient energy transfer (ET) from Ce3+ to Eu2+ appeared in the Ce3+-Eu2+ codoped samples, and the yellow emission of Eu2+ can be further enhanced by this ET. The thermal-quenching luminescence of the as-prepared samples was evaluated by the temperature-dependent emission spectra, which indicated that the introduction of Sr2+ can improve the thermally luminescence stability of Eu2+. The fabrication of the LEDs device revealed that the Ce3+-Eu2+ activated samples in this work could show potential applications in white LEDs.
RESUMO
A series of Ca9La(PO4)5SiO4F2:Ce3+,Tb3+,Mn2+ (CLPSF:Ce3+,Tb3+,Mn2+) phosphors were obtained by a conventional solid-state reaction method, and the luminescence properties excited by ultraviolet light were investigated in detail. The Ce3+-doped CLPSF samples show near-ultraviolet luminescence with the dominant peaks around 361 nm. Different Ce3+ emission centers were identified from the emission spectra. When the Ce3+ and Mn2+ are codoped into the host, an energy transfer (ET) from Ce3+ to Mn2+ was found, owing to which the visible emitting-light-color has been tuned from blue to light brown. The corresponding ET mechanism was studied by employing Dexter's theory. In the Ce3+-Tb3+ codoped CLPSF phosphors, the tunable emission was realized on the basis of the ET between Ce3+ and Tb3+. To further obtain the white emissions with tunable correlated color temperature, the Ce3+-Tb3+-Mn2+ tridoped CLPSF samples were designed, and the ET relationship in these phosphors were discussed. By studying the thermally luminescent properties, it was found that the Ce3+ and Mn2+ emission intensities in the CLPSF:Ce3+,Mn2+ samples showed different decrease rates with increasing temperature. The fluorescence intensity ratio (FIR) technique was used to investigate the temperature-sensing performance. On the other hand, the CLPSF:Ce3+,Tb3+ and CLPSF:Ce3+,Tb3+,Mn2+ phosphors exhibit relatively high thermally luminescent stability. The above discoveries indicate that the developed phosphors could have potential applications in LEDs and optical thermometer.