Improved optical properties of phosphors-in-glass through the optimal size distribution of glass powder.

White-light diodes (WLEDs) are widely used in high-brightness applications owing to their outstanding advantages. However, current methods for preparing commercial WLEDs significantly deteriorate their optical properties and limit their use in high-power applications. To address this, inorganic materials, such as phosphor-in-glass (PiG), have been recently investigated as practical alternatives. In this study, a series of high-efficiency white-emitting PiG samples were prepared by mixing silicate glass powders with different particle size distributions and different concentrations of Y3Al5O12:Ce3+ (YAG:Ce3+) phosphors. The microstructure, transmittance, and photoluminescence properties of PiG were investigated. When the glass powder with the particle size ranges of 75-150 and 30-48 µm were mixed, at a ratio of 94 : 6, a silicate glass with a thickness of 0.8 mm and a maximum transmittance of 75% in the visible range was obtained. Under excitation with a 450 nm blue-light laser diode, PiG produced white light with a total luminescence efficiency of 194.64 lm W-1 and a total luminous flux of 623.9 lm. These results demonstrate that the optical performance of PiG can be effectively adjusted by adjusting the particle size distribution of silicate glass powder and the mixing concentration of the YAG:Ce3+ phosphor, thereby providing a tuning pathway for smart white-light devices.

Dual-mode optical thermometry design in K3YSi2O7:Eu multi-site phosphor.

In this study, a dual-mode optical thermometer is designed based on radiative transitions from Eu3+ and Eu2+ ions at different K3YSi2O7 lattice sites. In the luminescence-intensity-ratio strategy, a ratiometric signal composed of Eu3+:5D0→7F1 and Eu3+:5D0→7F2 emissions at 593 and 616 nm, respectively, is employed. Meanwhile, the intensity ratio of the 593-nm emission under O2-→Eu3+ charge transfer excitation (λex = 249 nm) to that upon Eu2+:4f7→4f65d1 excitation (λex = 349 nm) is selected as a thermometric parameter in the single-band-ratio approach. The study findings show that combining the two strategies is conducive to the improvements in sensing-sensitive and anti-interference performance.

Highly precise FIR thermometer based on the thermally enhanced upconversion luminescence for temperature feedback photothermal therapy.

A highly precise temperature-feedback photothermal therapy platform in deep tissue is proposed based on all-fiber fluorescence intensity ratio (FIR) thermometry, which provides a promising route to realize real-time temperature monitoring in the minimally invasive treatment of tumors. Highly disordered double perovskite Li2Zn2Mo3O12 (LZMO) phosphors doped with rare earth ions were prepared and intense green upconversion emissions were observed with an ultra-low excitation power. The thermal enhancement of the upconversion luminescence was achieved up to 423 K, which is very beneficial to achieve a good signal-to-noise performance during the temperature-rise period. Superior temperature sensing performance was demonstrated with the maximum absolute sensitivity of 89.9 × 10-4 at 423 K. The strong upconversion emissions and high temperature sensitivity result in a small temperature error (±0.4 K). The integrated bifunctional needle could simultaneously realize temperature measurement and laser heating, which was exhibited in the denaturation of egg white and laser ablation of the porcine liver in vitro.

Synthesis of ZrO2:Pr3+,Gd3+ nanocrystals for optical thermometry with a thermal sensitivity above 2.32% K-1 over 270 K of sensing range.

Nowadays, there is enthusiastic effort to develop luminescent thermometers used for remote and high-sensitivity temperature readout over a wide sensing range. Herein, Pr3+ and Gd3+ co-doped ZrO2 nanocrystals are designed, prepared and investigated by XRD, Raman spectroscopy, XPS, TEM, EDS, DRS, PLE and PL spectroscopy. Upon 275 nm irradiation, the PL spectrum of ZrO2:Pr3+,Gd3+ is found to be composed of a narrow emission peak at 314 nm (Gd3+ 6P7/2-8S7/2), a broad defect-related emission band at 400 nm, and several emission peaks in the wavelength region of 585-700 nm (Pr3+ 1D2-3H4, 3P0-3H6, and 3P0-3F2), which exhibit different thermal responses owing to the effects of the various non-radiative relaxation processes and trap energy levels. Accordingly, the luminescence intensity ratio (LIR) between the Pr3+ 1D2-3H4 and Gd3+ 6P7/2-8S7/2 transitions demonstrates excellent relative sensing sensitivity values ((2.32 ± 0.01)% K-1-(8.32 ± 0.05)% K-1) and low temperature uncertainties (0.08 K-0.28 K) over a wide temperature sensing range of 303 K to 573 K, which are remarkably better than those of many other luminescence thermometers. What is discussed in the present study may be conducive to broadening the research region of RE3+ doped luminescence thermometric phosphors, especially for materials with rich 4f-4f transition lines and defect-related luminescence.

Ln3+ doped phosphor-in-glass: A new choice of color filter for wide-color gamut white light-emitting diodes.

Phosphor-in-glass (PiG) is a novel fluorescent color conversion material that is an excellent choice for preparing wide-color gamut white LEDs due to its excellent thermal stability, high efficiency and facile preparation process. To the best of our knowledge, this paper is the first to widen the color gamut of the white LED from 77.33% to 92.02% by doping the PiG substrate with two kinds of lanthanide ions: Er3+ and Nd3+. The low sintering temperature and suitable preparation process has ensured the phosphor and glass become compounded independently together while still exhibiting good luminescence performance; this has been demonstrated via X-ray diffraction and field emission scanning electron microscopy. The influence of doping the host glass with Ln3+ ions has been explored, specifically considering the effects on the color gamut, the color coordination, the correlated color temperature and the color rendering index. The results presented herein have demonstrated that the Er3+/Nd3+-doped PiG is a promising candidate as a color filter in the domain of wide-color gamut white LED.

Efficient Er3+:4I11/2 → 4I13/2 radiative transition regulated by optimizing the sensitization mechanism.

A series of fluorophosphates glass codoped with active Er3+ ions and sensitizing ions of different systems were prepared to systematically study their sensitization effect in order to obtain efficient MIR luminescence. Differential scanning calorimetry curve indicates the favorable thermal stability of the glass host. A comprehensive analysis of the sensitization mechanism is given based on the synthesis considering the position and intensity of fluorescence emissions together with the lifetime of Er3+:4I13/2 active level. The results show two positive sensitization effects: the eliminating effect to the lower laser level of Er3+ active ions represented by Pr3+ ions reducing the lifetime of 4I13/2 energy level to a great extent; and improving the absorption efficiency of pumping source sensitized by Yb3+ ions. The paper has provided a mental knowledge for sensitization mechanism in rare earth multi-doped materials together with the aiming of promoting the MIR luminescence of Er3+ ions.

Effects of Tm3+ concentration on upconversion luminescence and temperature-sensing behavior in Tm3+/Yb3+:Y2O3 nanocrystals.

The effects of Tm3+ concentration on upconversion emission and temperature-sensing behavior of Tm3+/Yb3+:Y2O3 nanocrystals were investigated. Blue and red emissions were observed under 980 nm excitation. Both upconversion emissions and the blue to red intensity ratio were found to decrease with increasing Tm3+ concentration. The temperature-sensing performances of the samples were studied, the fluorescence intensity ratio of 1G4(a)→3H6 (477 nm) and 1G4(b)→3H6 (490 nm) transitions from Tm3+ ions was chosen as the thermometric index. The results showed that the sensor sensitivity was sensitive to Tm3+ ion concentration. The maximum sensitivity of ~32 × 10-4 K-1 was obtained for 0.1%Tm3+/5%Yb3+:Y2O3 nanocrystals at 344 K. Moreover, a marked optical induced heating effect was also found in the nanocrystals. The prepared Tm3+/Yb3+:Y2O3 nanocrystals could be used in temperature-sensing probes and in optical heaters.

Tuning the micro-structure of germanosilicate glass to control Bi0/Bi+ and promote efficient Ho3+ fluorescence.

Bi can exist in a variety of chemical states (with varying ionic charges) and the microstructure of the glass surrounding the ions can be engineered to manipulate the chemical state. In this work, efficient enhancement of Ho3+ emission is observed with the change in local glass environment around Bi by adding Al2O3 to multi-component germanosilicate glass. In this multi-component glass, Al3+ can form tetrahedral AlO4 by accepting the non-bridging oxygen (NBO) and then, the addition of the AlO4-tetrahedron to the glass network facilitates the diffusion of alkali metals. Hence, Al2O3 decreases the Ba2+-rich domain and is conducive to the existence of Bi ions that are at low valence state. Moreover, the emission spectra indicate high efficiency energy transfer (ET) derived from NIR emission centers (Bi0/Bi+) located in close proximity to the Ho3+ ions. These results indicate that the optimized fluorescence of Ho3+ for optical fiber laser can be achieved by adjusting the local structure of the host glass.

Controllable structural tailoring for enhanced luminescence in highly Er3+-doped germanosilicate glasses.

Higher concentrations of rare earth (RE) ions in glass materials would be favorable for the output of single-frequency fiber lasers. In this Letter, we adjusted the topological structure of glass networks through controlling the numbers of non-bridging oxygens (NBOs) and bridging oxygens (BOs) by tuning the composition of the glasses, hence increasing the RE doping concentration of germanosilicate glasses. The increased flexibility of the glass networks favors the distribution of clusters of RE ions to decrease fluorescence quenching, which was validated by both our experimental and theoretical results. To the best of our knowledge, for the first time, a highly Er3+-doped (up to 7 mol. %) heavy metal oxide glass was fabricated without quenching by tuning the components of the glass. In addition, we have demonstrated an approach to enhance the fluorescence properties of heavily RE-doped glass materials by tailoring network topology.

Enhanced 3 µm luminescence properties based on effective energy transfer Yb3+ : 2F5/2→Dy3+ : 6H5/2 in fluoaluminate glass modified by TeO2.

Enhanced 3 µm luminescence of Dy3+ based on the effective process of Yb3+:F5/22→Dy3+:H5/26 with a higher energy transfer coefficient of 7.36×10-39 cm6/s in fluoaluminate glass modified by TeO2 was obtained. The energy transfer efficiency from Yb3+ to Dy3+ in Dy3+/Yb3+ codoped glass was as high as 80%, indicating the effective energy transfer of Yb3+. The higher temperature of the glass transition (Tg) and larger characteristic temperatures (ΔT,Kgl) revealed better thermal properties of the prepared glasses compared with the traditional fluoaluminate glasses, which is of great benefit to fiber drawing. The lower hydroxyl content (15.7 ppm) indicated better fluorescence properties of the glass. It was noted that the longer lifetime of 572 µs and higher emission cross section of 5.22×10-21 cm2 along with the bandwidth of 245 nm around 3 µm proved potential applications in mid-IR laser materials of the present glass.