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A statistical model based on the condition of thermal and diffusive equilibrium between the conduction electrons and the electrons in the excited 5d 1 level of Ce3+ is presented. Using this model, we find the probability for an excited Ce3+ ion to be thermally ionized leading to an electron in the conduction band. The density of conduction electrons is then calculated over a wide range of temperatures and excitation densities. The observed quenching of emission at high temperature in Ce-doped YAG with low Ce concentrations is also investigated within this model. It is shown that the experimentally-observed nonradiative losses in this phosphor can be reasonably simulated assuming losses occur via nonradiative decay from the conduction band to the Ce3+ ground state. • We present a model of thermal ionization in YAG:Ce leading to conduction electrons. • The density of conduction electrons in YAG:Ce is calculated. • Conduction electron trapping by Ce4+ explains losses in YAG:Ce at high temperatures. • Discrepancy between activation energy and ionization energy is explained. [ABSTRACT FROM AUTHOR]

Here a strategy was proposed to realize the thermal enhancement of the green luminescence of Tb3+ ion through ground state thermal population. The 5D 4 -7F 5 emission line of Tb3+ ion was observed under the excitation of a commonly used 405 nm laser diode for the first time, to the best of our knowledge. Its intensity was found to increase by ten times upon increasing the temperature from 343 to 783 K. Moreover, this change law was in good accordance with the Boltzmann distribution. It was confirmed that the thermal population of the 7F 5 state at the expense of the depopulation of the 7F 6 ground state, namely the ground state thermal equilibrium, should be responsible for this uncommon phenomenon. For comparison, the Xe lamp was also used to directly excite the 7F 6 -5D 3 absorption line of Tb3+ ion. In this case, the 5D 4 -7F 5 emission line of Tb3+ ion was also observed. Different from the former case, this line decreased monotonously upon increasing the temperature over the experimental range. The reason for this change law was also discussed. Image 1 [ABSTRACT FROM AUTHOR]

Tm3+,Ho3+-codoped and compositionally "mixed" disordered Ca(Ga,Lu)AlO 4 aluminate crystals are promising materials for ultrashort pulse generation above 2 μm. Their polarized spectroscopic properties are studied and the effect of Lu3+ codoping on the inhomogeneous spectral broadening is verified. The peak stimulated-emission cross-section for the 5I 7 → 5I 8 Ho3+ transition is 1.05 × 10−20 cm2 at 2000 nm for π-polarization. The Tm3+ ↔ Ho3+ energy-transfer parameters are P 28 = 1.42 and P 71 = 0.090 [10−22 cm3μs−1] indicating a direct transfer with a thermal equilibrium time of 4.35 ms. The effective gain spectra for the codoped crystal are derived. For σ-polarization, the gain bandwidth at ∼2.04 μm is about 100 nm; particularly for this light polarization, Lu3+ codoping induces a noticeable red-shift of the emission spectra further beyond 2 μm. Using absorption studies at 12 K, the Stark splitting of the Tm3+ and Ho3+ multiplets is resolved. A laser-pumped Tm,Ho:Ca(Ga,Lu)AlO 4 laser generated a maximum output power of 763 mW at 2078.6 nm with a slope efficiency of 26.4% and π-polarized emission. A continuous wavelength tuning between 1887.7 and 2127 nm (tuning range: 239.3 nm) was achieved for σ -polarization. Diode-pumped operation of a -cut and c -cut crystals was also studied. • Tm3+,Ho3+-codoped "mixed" disordered Ca(Ga,Lu)AlO 4 aluminate crystal. • The effect of Lu3+ codoping on the inhomogeneous spectral broadening is verified. • For σ-polarization, the gain bandwidth at ∼2.04 μm is about 100 nm. • The Tm,Ho:Ca(Ga,Lu)AlO 4 laser generated 763 mW at 2078.6 nm in π-polarization. • A continuous wavelength tuning between 1887.7 and 2127 nm was achieved. [ABSTRACT FROM AUTHOR]

An Er 3+ -doped calcium aluminate glass has been studied in order to establish its suitability as optical temperature sensor based on the fluorescence intensity ratio technique. Temperature-induced changes in the relative intensities of the green emissions associated with the transitions from the 2 H 11/2 and 4 S 3/2 thermalized levels to the 4 I 15/2 ground state under laser excitation at 488 nm has been measured in the range of temperatures from 150 to 762 K. The sensitivity obtained due to temperature changes shows a maximum of 159×10 −4 K −1 at 645 K, one of the highest sensitivity values found in Er 3+ -doped host matrices. Compared to other studies, a different approach has been followed to estimate the calibration the temperature sensor using a low-cost prototype. [ABSTRACT FROM AUTHOR]

The 4I 15/2 /4F 9/2 states of Dy3+ ion are attractive as they have been confirmed to be thermally linked and thus can be used for luminescent ratiometric thermometry. Traditionally, this thermally coupled property is confirmed by using the Boltzmann distribution formula, which is, however, not so reliable as the fitted energy gap between thermally coupled states is sometimes different from the real value. Here we present a more hard evidence to support that the 4I 15/2 /4F 9/2 states of Dy3+ ion are indeed in thermal equilibrium. The time resolved luminescence originating from the 4I 15/2 /4F 9/2 states of Dy3+ ion in calcium tungstate host has been studied as a function of temperature from 333 to 773 K. It is found that the 4I 15/2 /4F 9/2 states always own the same lifetime over the whole experimental temperature range, which is increased from 211 to 238 μs, suggesting undoubtedly that the 4I 15/2 /4F 9/2 states are thermally coupled all the time. As an added benefit, it is confirmed that lifetime thermometry can be exploited by using the 4I 15/2 /4F 9/2 states. In the end, its sensing performance, i.e. relative sensitivity, is compared with the temperature sensing method that depends on the luminescence intensity ratio between the 4I 15/2 -6H 15/2 and 4F 9/2 -6H 15/2 transitions of Dy3+ ion. The results reveal that the lifetime thermometry has a lower thermal sensitivity. Image 1 • The 4I 15/2 /4F 9/2 states of Dy3+ were studied. • Their lifetimes were confirmed to be same. • Lifetime- and luminescence ratiometric-thermometry were developed. [ABSTRACT FROM AUTHOR]

Non-contact optical thermometer appears to be excellent alternative for traditional contact thermometer. Fluorescence intensity ratio (FIR) via thermally-coupled energy levels (TCELs) of one certain lanthanide ion is most adopted method to measure temperature. However, there is an inevitable dilemma in this method that large energy gap (EG) of TCELs is required for gaining highly relative sensitivity (S r) while small EG is needed for achieving highly absolute sensitivity (S a). Meanwhile, the EG of TCELs cannot exceed a certain value for achieving thermal equilibrium. To solve this issue, in this work, a new strategy based on synergistic luminescence from Ce3+ and Tb3+ codoped in SrAl 2 Si 2 O 8 (SASO) has proposed for obtaining highly sensitivity over a wide temperature range. FIR of Ce3+ to Tb3+ in this self-referencing and dual-emitting phosphor shows remarkable contrary temperature dependence and has well fitted linear relationship, owing to resonance energy transfer (ET) from Ce3+ to Tb3+. Meanwhile, the emitting color of the phosphor is gradually shifted from blue to green with temperature, which means it is also potential candidate as colorimetric luminescent thermometer. These results could provide useful inspiration for designing stable and highly sensitive optical thermometer based on ET induced by synergistic luminescence. Integrated "weak/strong coupling" luminescence systems SASO: Ce, Tb for high performance thermometry. Image 1 • S 1-3(x+y)/2 ASO: xCe3+, yTb3+ obtained via facile solid-state reaction. • The synergistic luminescent phosphor show remarkable temperature sensitivity. • Configurational coordinate diagram explained the temperature-dependent optical properties. [ABSTRACT FROM AUTHOR]