Upconversion Luminescence Spectra Research Articles

Huge enhancement in upconversion luminescence near-infrared emission of KYb (MoO4)2: Er3+ phosphor by doping Y3+ ions

The KYb(MoO4)2: Er3+, Y3+ phosphors were synthesized by high temperature solid state reaction method. By further doping Y3+ ions, the near-infrared (NIR, 804 nm, 4I9/2 → 4I15/2) luminescence of KYb(MoO4)2: 0.1 % Er3+ phosphor is greatly enhanced. Based on the upconversion luminescence (UCL) spectra, the optimal doping concentration of Y3+ ions were 7.5 %. Its near-infrared UCL intensity is about 26.9 times that of undoped Y3+ ions. Through a series of characterization methods, we find that the enhancement of NIR upconversion emission is due to the generation of defect bands. It plays a crucial role in facilitating the transfer of energy from green light level (2H11/2, 4S3/2) to red light level (4F9/2) and near-infrared level. To explain the luminescence mechanism, the power dependence, UV-VI-NIR absorption spectra, excitation spectra at 804 nm and emission spectra at 380 nm were studied. In addition, the 804 nm single near-infrared UCL intensity of KYb (MoO4)2: Er3+, Y3+ shows a linear variation with temperature in the temperature range of 298 K–673 K. The maximum sensitivity is 0.13 % K−1. This study provides a new method and theoretical support for the application of near-infrared UCL in optical temperature measurement.

Upconversion Emission and Dual-Mode Sensing Characteristics of NaYF4:Yb3+/Er3+ Microcrystals at High and Ultralow Temperatures.

In this study, we investigate micrometer-sized NaYF4 crystals double-doped with Yb3+/Er3+ lanthanide ions, designed for temperature-sensing applications. In contrast to previous studies, which focused predominantly on the high-temperature regime, our investigation spans a comprehensive range of both high and ultralow temperatures. We explore the relationship between temperature and the upconversion luminescence (UCL) spectra in both frequency and time domains. Our findings highlight the strong dependence of these spectral characteristics of lanthanide-doped NaYF4 crystals on temperature. Furthermore, we introduce a dual-mode luminescence temperature measurement technique, leveraging the upconversion emission intensity ratio for both green and red emissions. This study also examines the correlation between temperature sensing, energy level disparities, and thermal coupling in Er3+ ions across various temperature scales. Our research contributes to advancing the understanding and application of lanthanide-doped materials, setting a foundation for future innovations in temperature sensing across diverse fields.

Up-converted white light emission in Er3+ doped MgAl2O4 nanocrystals

This work presents the influence of host defect centers on the photoluminescence characteristics of Mg1−xErxAl2O4 (x = 0.005, 0.01, and 0.03) nanocrystals under UV and near-infrared (NIR) excitations. The spinel-structured nanocrystals are synthesized through the combustion method. The Rietveld refinement and nuclear magnetic resonance analyses estimated the Er3+ ion occupancy at octahedral and other random sites of the MgAl2O4 lattice, and the existence of various lattice defects. Diffuse reflectance spectra showed broad bands attributed to oxygen vacancies as well as antisite defects and sharp peaks attributed to f–f transitions of Er3+ ions. The upconversion luminescence spectra consisted of sharp emission lines, ascribed to Er3+ ions, in the green and red wavelength regions, which overlapped over the broad curve attributed to intrinsic defects. Further, the UV excited downconversion luminescence spectra showed two broad emission bands in blue–violet and red-NIR regions with a very weak Er3+ ion emission feature. This up- and downconversion emission revealed energy transfer between host and Er3+ ions via intrinsic defects. As a result, the emission color changes from bluish purple to white by varying the excitation wavelength from UV to NIR. This rare earth activated luminescence from MgAl2O4 nanocrystals would exhibit potential applications in display devices and solid-state lighting.

Exploring energy mechanisms involved in the luminescence reduction due to Ce3+ doping via core-multishell upconversion nanoparticles highly doped with Ho3+ and Yb3+

Upconversion nanoparticles (UCNPs), particularly those that are highly doped, possess outstanding properties and have demonstrated tremendous application potential. However, novel fine-tuning strategies are urgently required to enhance the upconversion luminescence (UCL) performance of UCNPs. In this study, a series of core–multishell UCNPs highly doped with Ho3+ and Yb3+ ions were synthesized via the oleate route. The X-ray diffraction (XRD), transmission electron microscopy (TEM), and UCL spectra and decay times, and pump power dependency of the synthesized UCNPs were used to examine their morphology, size, and the UCL properties. Ce3+ ions were introduced to enhance Ho3+-based red UCL, and their doping strategy was also optimized based on summarized UCL trends and detailed UCL mechanism analysis. NaHoF4:Gd3+@NaGdF4:Yb3+,Ce3+@NaGdF4:Yb3+ UCNPs that had 10 mol% Ce3+ dopants in their middle shells exhibited better UCL properties than the larger traditional NaGdF4:Yb3+,Ce3+,Ho3+ UCNPs, probably because of the combined influence of the energy interactions between the Ce3+ ions and surface groups, sensitizing energy enhancement by active shells, and the positive cooperation between the Ce3+ ions and highly-doped core–shell structures. In this study, the phenomenon of UCL decrease resulting from Ce3+ ion doping was explored. Using unique core–multishell structures with highly-doped activators and sensitizers placed within and outside the structures, respectively, the UCL decrease due to Ce3+ ion doping was attributed to a competition for photons. Doping the UCNPs with Ce3+ ions near the UCNP surfaces favors Ho3+-based red UCL. Our study findings can deepen the understanding of the Ho3+-based UCL mechanisms and increase the potential uses of NaHoF4 materials in photo-induced therapy.

Rapid detection of microalgae cells based on upconversion nanoprobes.

The quantification of microalgae cells is crucial for the treatment of ships' ballast water. However, achieving rapid detection of microalgae cells remains a substantial challenge. Here, we develop a new method for rapid and effective detection of microalgae concentration by utilizing upconversion nanoprobes (UCNPs) of NaYF4:Er3+,Tm3+. Three ligands, carboxylated methoxypolyethylene glycols with 5000 and 2000 molecular weights (mPEG-COOH-5, mPEG-COOH-2) and D-gluconic acid sodium salt (DGAS), were used to convert hydrophobic UCNPs into a hydrophilic state through modification. The results show that the mPEG-COOH-5 modified UCNPs present the highest stability in an aqueous solution. Fourier Transform Infrared Spectroscopy (FTIR) measurements reveal the presence of a significant number of -COOH functional groups on UCNPs after the mPEG-COOH-5 modification. These -COOH groups enhance the hydrophilicity and biocompatibility of UCNPs. The soluble UCNPs were directly mixed with microalgae, and the upconversion luminescence (UCL) spectra of the UCNPs were recorded immediately after thorough shaking. This greatly reduces the measurement time and could realize rapid onboard detection. In this sensing procedure, the UCNPs with red UCL functioned as energy donors, while microalgae with red absorption served as an energy acceptor. The UCL gradually diminishes with an increase in microalgae concentration based on the inner filter effect, thus establishing a relationship between UCL and microalgae concentration. The accuracy of the detection is further validated through the traditional microscope counting method. These findings pave the way for a novel rapid strategy to assess microalgae concentration using UCNPs.

Order-disorder phase transitions significantly improving the upconversion luminescence intensity of BiTa7O19:Er3+/Yb3+

BiTa7O19 (BTO) has two lattice structure, P–6C2 (188) ordered phase and P63/mcm (193) disordered phase. Ordered and disordered BTO:Er3+/Yb3+ upconversion phosphors (UCPs) were obtained by solid sintering with different temperatures. The lattice structure of all the samples was investigated by XRD, SEM and Raman spectroscopy, and upconversion luminescence (UCL) spectra were tested by spectrometers. The green integral UCL intensity of the disordered BTO:Er3+/Yb3+ UCP is 60.76 times than that of the ordered sample. By comparing Er3+/Yb3+ co-doped and Er3+ single-doped UCPs with different structures, it is found that the disordered structure enhances the energy transfer from Yb3+ to Er3+, which may be caused by the disordered structure reducing the distance between Yb3+ and Er3+. The absolute temperature sensitivity of the sample with the highest UCL intensity is 0.01005 K-1 at 352 K. All results suggest that the disordered structure of BTO host can greatly improve green UCL intensity and the disordered BTO:Er3+/Yb3+ UCPs are suitable for the application of optical temperature measurement.

Preparation and up-conversion luminescence properties of Er: YbAG and Er: YAG single crystals

High quality optical single crystals of cubic Yb2.96Er0.04Al5O12 and Y2.96Er0.04Al5O12 were successfully prepared using the OFZ method. The 980 nm photon absorption intensity by Yb2.96Er0.04Al5O12 crystal is much larger than that in Y2.96Er0.04Al5O12 crystal, the transmission of Yb2.96Er0.04Al5O12 crystal is lower than that of Y2.96Er0.04Al5O12 crystal, because the density of Yb2.96Er0.04Al5O12 single crystal (6.604 g/cm3) is larger than that of Y2.96Er0.04Al5O12 single crystal (4.529 g/cm3). The up-conversion luminescence spectra of the crystals excited by 980 nm laser show several distinct groups of emission peaks at ∼544 and ∼556 nm, as well as ∼650 and ∼667 nm. The peak intensities of the up-conversion luminescence spectrum for the Yb2.96Er0.04Al5O12 crystal were much higher than those for the Y2.96Er0.04Al5O12 crystal. Overall, the results of the present study suggest that Yb2.96Er0.04Al5O12 single crystal may have advantages over Y2.96Er0.04Al5O12 single crystal for luminescence in solid-state lasers.

Effect of Zn2+, S2−, Mo4+ and V5+ single doped BiTa7O19:Er3+/Yb3+ on upconversion luminescence intensity under 980 nm laser excitation

On the basis of BiTa7O19 (BTO):0.1Er3+/0.4 Yb3+, Zn2+, S2−, Mo4+ and V5+ single doped upconversion phosphors (UCP) were successfully prepared by solid phase sintering. The lattice structure, particle size and diffuse reflectance spectra were measured by X-ray diffraction, scanning electron microscope and spectrophotometer. Upconversion luminescence (UCL) spectra of these UCP were investigated under 980 nm laser excitation with power density from 1.82 to 124.99 W/cm2. Zn2+ doped UCP can obtain the highest UCL intensity when excitation power density is less than 56.91 W/cm2, and Mo4+ doped UCP can obtain the highest UCL intensity when excitation power density is from 56.91 to 124.99 W/cm2. The UCL intensity of all samples increases first and then decreases with the increase of excitation power. By measuring UCL intensity changes with the excitation power of the UCP mixing with BN and UCP in vacuum and atmosphere, the experimental results show that the increase of temperature caused by laser excitation is the reason for the decrease of UCL intensity under high power excitation. Utilizing LIR technology, it is proven that at high power 90.95 W/cm2, Mo4+ and Zn2+ single doped can decrease and increase the UCP temperature under the same power density excitation compared with BTO:0.1Er3+/0.4 Yb3+, respectively. The maximum relative temperature sensitivity of all UCP is calculated in the range of 0.00767–0.00854 K−1 at 303 K. All experiments show that Zn2+ and Mo4+ single-doped UCP are suitable for temperature sensing and luminescence imaging under low and high-power excitation, respectively.

Color tunable upconversion luminescence from ex-situ sol-gel derived Titania-Silicate dense glass-ceramic co-doped with Pr3+-Yb3+ ion pair

Praseodymium–Ytterbium (Pr3+-Yb3+) ion pair co-doped with Silica-Titania dense glass ceramic material was synthesized by novel ex-situ sol-gel method after annealing at ca. 900 °C and investigated for their morphological, structural and luminescence characteristics. Color-tunable upconversion luminescence (UCL) are observed from varying Yb3+ (X mol%; X = 0.0, 0.7, 1.5, 3.0) and fixed Pr3+ (0.7 mol%) ions co-doped ex-situ sol-gel silicate-titania (STPYX) dense glass-ceramic (DGC) materials under 980 nm laser diode pumping source due to the transfer of energy from the Yb3+→ Pr3+ ion. An original ultra-broadband UCL spectra is achieved from the STPYX-DGC materials for excitation photon of wavelength (λex = 980 nm) for varying Yb3+ ion concentration, where the optimized UCL has been observed for material with 1.5 mol% Yb3+ ion concentration. Further, two dimensional spatially resolved photoluminescence intensity distribution study has also been performed using 2D-PL confocal mapping throughout the STPY15-DGC material for a similar excitation source. The color tunability from white to red is evident from the CIE co-ordinate of corresponding UCL spectra of the as-synthesized materials at different activator (Yb3+) ion concentrations. An intense absorption spectrum with peaks assigned to both Pr3+ and Yb3+ ions is also observed for the STPY07-DGC material.

Tremendous enhancement of green emission from Er3+/In3+ co-doped β-Ga2O3 ultrawide bandgap semiconductors

Er3+ singly doped and Er3+/In3+ co-doped gallium oxide ceramics with intense green emission were prepared using the conventional solid-state reaction method. The Ga2-x-yErxInyO3 ceramics exhibit green and red emission at 555 and 673 nm, and follow the two-photon absorption process under the excitation of 980 nm. Systematic measurements of the upconversion luminescence spectra of Ga2-x-yErxInyO3 show that the optimal doping concentrations, sintering temperature and time are x = 0.015, y = 0.035, 1250 °C, and 8 h, respectively. For a fixed Er3+ doping concentration of x = 0.015, the green emission intensity at 555 nm can be enhanced by 60 folds through 3.5 mol% In3+ doping, which is attributed to reduced non-radiative decay, enhanced energy transfer from In3+ ions to Er3+ ions via defect states, and increased photon absorption. The introduction of 3.5 mol% In3+ also increases the fluorescence lifetime by 235–272%. These observations provide compelling evidence for the presence of effective energy transfer between In3+ and Er3+ ions.

Effects of Er3+ and Yb3+ concentrations on upconversion luminescence and thermal sensing characteristics of Sc2O3:Er3+/Yb3+ phosphors

Sc2O3:Er3+(x mol%)/Yb3+(3 mol%) (x = 0.3, 0.5, 0.7) and Sc2O3:Er3+(0.5 mol%)/Yb3+(y mol%) (y = 1, 3, 5) phosphors were synthesized by CO2 laser zone-melting method. The upconversion luminescence (UCL) spectra of Sc2O3:Er3+/Yb3+ fluorescent materials, which were pumped by 980 nm, were measured and analyzed. The results show that the UCL intensity reaches maxima when doped with 0.5 mol% Er3+ and 3 mol% Yb3+, and the increase of Yb3+ concentration leads to reduce the ratio of green UCL to red UCL. The temperature-dependent UCL spectra of Sc2O3:Er3+/Yb3+ fluorescent materials with various Er3+ and Yb3+ concentrations were measured from 290 K to 1023 K, and the thermal sensing characteristics were revealed via the fluorescence intensity ratio (FIR) technique. The maximal relative sensitivity (SR) are almost independent of the Er3+ and Yb3+ concentration, while the maximal absolute sensitivity (SA) increases with Yb3+ concentration in the whole measurement range. Among the prepared samples, the maxima of SA and SR are achieved for the sample of Sc2O3:Er3+(0.5 mol%)/Yb3+(5 mol%)，with the values of 5.34 × 10−3 K−1 (364.1 K) and 12.5 × 10−3 K−1 (290 K), respectively. Interestingly, for Sc2O3:Er3+ (0.5 mol%)/Yb3+ (3 mol%), having the highest UCL intensity, its maximum SA and SR are 4.90 × 10−3 K−1 (371.4 K) and 11.2 × 10−3 K−1 (290 K). The wide temperature sensing range and relatively high sensitivities of the fabricated materials provide excellent potential for temperature sensing.

Thermal Effects in Up-Conversion Luminescence NaYF4: Tm3+, Yb3+ Core-Shell Nanoparticles in the Temperature Range of 18-312 K.

This work demonstrates the temperature (18-312 K) impact on Tm3+ up-conversion luminescence in core-shell structured NaYF4:Tm3+, Yb3+ nanoparticles excited at 976 nm. As the temperature decreases from room temperature to 18 K, Tm3+ up-conversion luminescence bands intensities greatly increase, an average of 60-fold, emitting intense blue and ultraviolet radiation. Tm3+ up-conversion luminescence spectra measurements at different temperatures reveal that three thermal quenching mechanisms are responsible for observed variations in Tm3+ up-conversion luminescence spectra. These three quenching mechanisms are related to the excitation radiation absorption, Stark sublevel population, and energy transfer from Yb3+ to Tm3+.

SPR studies in PVA composite films of SiO2@NaYF4:Er3+/Yb3+ UCNPs via AuNPs concentration variation and their temperature sensing applications

The composite film of mesoporous silica coated NaYF4:Er3+/Yb3+ upconversion nanoparticles and gold nanoparticles (AuNPs) in Poly vinyl alcohol (PVA) medium were prepared. The effect of the concentrations of AuNPs with 0 µl, 50 µl, 100 µl and 150 µl on the structure and upconversion luminescence intensity were studied. The phenomenon of enhancement in upconversion luminescence intensity due to AuNPs were explained via surface plasmon resonance (SPR) phenomenon. Apart from this the XRD, FE-SEM and AFM studies were done for estimation of structure and surface morphology etc. The impurities were estimated through FTIR analysis. The optical properties of these polymer composite films were studied via UV–vis absorption spectra and upconversion luminescence spectra analysis. A low temperature sensing ability of these films have been demonstrated for the suitability of these films in bio-medical applications.

Structural and morphological characterizations of ex-situ sol-gel derived luminescent Nd3+-Yb3+ion co-doped zinc-silicate dense glass-ceramic

We proposed a novel ex-situ sol-gel synthesis of Nd3+ (0.7 mol%) and Yb3+ (X; X = 0.0, 0.7, 1.5, 3.0 mol%) ion co-doped Zinc-Silicate (SZNYX) dense glass-ceramic(DGC) samples. The structural analyses of the SZNY07-DGC sample were performed at different annealing temperatures using X-ray diffraction (XRD) analysis and Fourier transforms infrared (FTIR) spectroscopy. The tetragonal willemite Zn2SiO4 structure with an R-3(148) space group was confirmed from XRD results. The formation of the pure oxide phases (bridging oxygen) was noticed at FTIR spectra with the complete removal of hydroxyl impurity at higher annealing temperatures. The presence of ZnO crystallites with the inter-planer spacing of ⁓ 0.28 nm and Nd3+/Yb3+ ion pair in an amorphous silica host was confirmed via transmission electron microscopy (TEM) and TEM-energy dispersive spectroscopy (EDS) respectively. The white up-conversion luminescence (UCL) under a 980 nm excitation was attributed to the simultaneous emission of wavelength in the visible spectrum. The intensity of UCL was initially rising with an increase in Yb3+ ion concentration whereas the optimized luminescence was obtained for samples with 1.5 mol% Yb3+ ion concentration. The CIE chromaticity coordinates (0.34, 0.35) of corresponding UCL spectra were invariant with the change in Yb3+ ion concentration. The photoluminescence (PL) confocal mapping of the SZNY15-DGC sample was performed at different locations under a 980 nm laser excitation source which turned out non-uniform in nature throughout the surface. Thus as-synthesized SZNYX-DGC samples have spectacular upconversion luminescence for near-infrared excitation which may be utilized in thermal sensing, photovoltaic, displays, and photonic devices.

Efficient tunable temperature sensitivity in thermally coupled levels of Er3+/Yb3+ co-doped BaBi2Nb2O9 ferroelectric ceramic

Er3+/Yb3+ co-doped ferroelectric ceramic BaBi2-0.04-yNb2Er0.04YbyO9 (y = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10, and 0.12) are prepared by solid-state method and investigated for their structural and upconversion luminescence properties. High-resolution X-ray pattern investigation confirmed the ceramic's orthorhombic structure. Microstructure of sintered ceramic surface resembles plate-like structures and consists of non-uniform grains that are randomly oriented. Upconversion luminescence (UCL) spectra revealed two prominent green emission bands near 535 and 557 nm and a notable red band at 672 nm, corresponding to a 980 nm excitation wavelength. Decay time measurements support the effective energy transfer from Yb3+ to Er3+ ions. The average lifetime increases with increasing Er3+/Yb3+ doping concentration up to the optimal concentration (y = 0.10). Pump power dependence demonstrates that two photons are required to generate green and red UC illumination. The absolute sensitivity, Sa (0.69% K−1 and 0.58% K−1) and relative sensitivity, Sr (1.1% K−1 and 1.01% K−1) have been recorded for the first time on Er3+/Yb3+ co-doped BaBi2-0.04-yNb2Er0.04YbyO9 ceramic at y = 0.06 and 0.10, respectively, suggesting it is a viable non-contact sensor ceramic whose sensitivity can be tuned by varying dopant concentrations.

Crystal growth and infrared-to-visible upconversion luminescence in Nd-Yb-Tm: CaYAlO4 single crystal

Yb3+/Tm3+: CaYAlO4 (CYA) and Nd3+/Yb3+/Tm3+: CYA bulk single crystals were grown using the Czochralski (Cz) method. The polarized absorption, upconversion luminescence (UCL) spectra under 980 nm and 808 nm pumping, and fluorescence decay curves were measured as well as Judd-Ofelt (J-O) theory calculations were performed to investigate the sensitization effect of Yb3+ and Nd3+/Yb3+co-doping in Tm3+: CYA single crystal. Obvious enhancement was observed in Tm3+-activated crystals for the blue upconversion emission (∼474 nm) when doped with Yb3+ or co-doped with Nd3+/Yb3+. The energy transfer efficiency is 72.6% (Yb3+→Tm3+) and 71.7% (Nd3+→Yb3+/Tm3+) in Yb3+/Tm3+: CYA and Nd3+/Yb3+/Tm3+: CYA single crystals respectively. The gain cross-sections were calculated, and it can stated that the blue laser output derived from upconversion is possible around 474 nm related to the transition of 1G4→ 3H6 in Yb3+/Tm3+: CYA and Nd3+/Yb3+/Tm3+: CYA crystals.

Enhanced upconversion luminescence and single-band red emission in β-Ba2ScAlO5: Yb3+/Er3+ phosphor through doping Cu2+

This study reports on a single-band red upconversion emission of Er3+ in a pure-phase β-Ba2ScAlO5: Yb3+/Er3+ fluorescent powder by doping Cu2+. The optimum concentration of Cu2+ ions in β-Ba2ScAlO5: Yb3+/Er3+ powder was 0.20. The red and green emission intensity of β-Ba2ScAlO5: Yb3+/Er3+ sample with optimum concentration of Cu2+ ions increased by 19.1 and 3.6 times, respectively, relative to the β-Ba2ScAlO5:Yb3+/Er3+ material lacking Cu2+ ions. The red-green integral intensity ratio of the β-Ba2ScAlO5:Yb3+/Er3+/Cu2+ phosphor reached 141.9. The potential upconversion luminescence (UCL) mechanism was explored by analyzing the down-shift luminescence (DS) spectra, upconversion luminescence spectra, and upconversion fluorescence lifetime decay curves of Yb3+/Er3+/Cu2+ triple-doped β-Ba2ScAlO5. Enhanced red emission and green upconversion emission are achieved by energy transfer between defect band by the oxygen vacancy and Er3+ energy levels. This study's findings establish the foundation for developing novel phosphors with single UC red light emission, which has potential applications in illumination displays, optical thermometry, and biomedicine.

Design and preparation of white light emission from up-conversion transitions in Er3+/Tm3+/Yb3+ co-doped cubic zirconia single crystals

High-quality cubic YSZ crystals were designed with various contents of Er3+, Tm3+ and Yb3+ to produce white light emission, and grown by the optical floating zone method. The up-conversion luminescence spectra of the crystals under 980 nm laser irradiation show three distinct groups of emission peaks at ∼473 nm (blue) generated by the Tm3+1G4→3H6 transition, 531 and 547 nm (green) from the Er3+2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, and 640 and 662 nm (red) from the Er3+4F9/2 → 4I15/2 transition. The optical power curve obtained by plotting the up-conversion luminescence intensity against the laser power shows that the blue emission involves a three-photon process, whilst both the green and red emissions are the results of two-photon processes. Overall white light emission was observed with the crystal prepared with 0.05 mol% Er2O3, 0.5 mol% Tm2O3 and 2.0 mol% Yb2O3, and this crystal is suitable for use in highly efficient white light emission devices.

Impacts of Ce3+ doping on temperature sensing characteristics of LuAG: Yb3+/Ho3+ up-conversion fluorescent materials

A series of LuAG: 5 mol%Yb3+/0.5 mol%Ho3+/x mol%Ce3+ (x = 0, 0.2, 0.5, 1.0, 2.0) up-conversion (UC) fluorescent materials were prepared using CO2 laser heating zone melting method. The X-ray diffraction (XRD) patterns confirm that the prepared samples have a pure LuAG crystal phase. Under excitation of a 980 nm laser, the up-conversion luminescence (UCL) spectra of the prepared samples were obtained. Two UCL emission bands of Ho3+ ions were observed, including green emission band of the 5F4/5S2→5I8 transition, and red emission band of the 5F5→5I8 transition. Due to the cross-relaxation (CR) processes between Ce3+ ions and Ho3+ ions, the doping of Ce3+ ions can effectively improve the UCL efficiency of Ho3+ ions, and the emission intensity reaches maximum when doped with 1 mol% Ce3+. The temperature sensing characteristics of LuAG: Yb3+/Ho3+ and LuAG: Yb3+/Ho3+/Ce3+ from 303 K to 723 K were studied by fluorescence intensity ratio (FIR) method. By doping 1 mol% Ce3+ ions, the absolute sensitivity of the sample has been significantly improved, with the maximal absolute sensitivity of 0.0951 K−1 (303 K), and the maximal relative sensitivity of 0.0103 K−1 (343 K). The high sensitivity and wide measurement range make LuAG: Yb3+/Ho3+/Ce3+ UCL material ideal for temperature sensing.

Photon up-conversion in Er3+ ion-doped ZnO-Al2O3-BaO-B2O3 glass for enhancing the performance of dye-sensitized solar cells

One of the main limitations in the development of dye-sensitized solar cell (DSSC) is contributed by the optical losses that occur within the absorber layer due to spectral mismatch. DSSC typically only absorbs solar light within the visible region (i.e. up to 800 nm), while the photon energy in the infrared region remain unutilized. Here we report the integration of Er3+ ion-doped glass as up-conversion (UC) element in DSSC and study their effect on the photovoltaic performances. Several characterizations were conducted including physical, structural, optical, luminescence, and radiative properties on the glass sample, while current-voltage and incident photon-to-current conversion efficiency characterization were conducted to analyze the electrical properties of DSSC. The UC luminescence spectra of the glass sample under 800 nm excitation showed green light emissions that were located between 531 and 553 nm. The UC luminescence band of glass sample was confirmed suitable with the absorption band of Z907 dye. After placing the UC glass below the DSSC’s counter electrode side, the power conversion efficiency of DSSC were mostly positively affected by the presence of UC glass, where the highest improvement of around 7.21 % was obtained for DSSC coupled with 2.0 mol% of Er3+ ion-doped glass. The enhancement was primarily attributed to the improved light harvesting due to the UC mechanism within the device as indicated by the increase in external quantum efficiency and fill factor. Our contribution provides a simple yet versatile approach in improving DSSC performance via the application of a free standing Er3+ ion-doped up-conversion glass.