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Abstract: Polarized visible and infrared emission characteristics of Er3+ ions in vapor-transport-equilibration (VTE)-treated LiNbO3 crystals codoped with different concentrations of Zn and Er were investigated in comparison with corresponding as-grown crystals. The results show that the VTE treatment leads to substantial spectral changes of Er3+ emissions at 0.65, 0.98 and 1.5μm regions, and the spectral changes in the 0.98 and 1.5μm regions appear to be Zn-concentration-dependent. It is concluded in combination with X-ray powder diffraction results and optical absorption characteristics reported previously that the VTE treatment resulted in crystalline phase transformation with respect to Er3+ ions from original LiNbO3 to ErNbO4 phase in all crystals studied. The formation of the ErNbO4 phase and the Zn2+ codopants are responsible for the VTE-induced substantial spectral changes. The emission characteristics of the ErNbO4 precipitates in the Zn/Er-codoped crystals are found to be very different from those of the ErNbO4 precipitates in the only Er-doped crystal in the infrared region, and the difference is attributed to the influence of the Zn2+ codopant on the Er3+ ion environment. The mechanism of the crystalline phase transformation is qualitatively explained from the viewpoint of the declined solubility of Er3+ ion in a Li-rich LiNbO3 crystal and from the phase diagram of Li2O–Nb2O5 system. [Copyright &y& Elsevier]

Abstract: Er3NbO7 phosphor was synthesized by sintering a mixture of Er2O3 and Nb2O5 powder in a molar ratio of 3:1 at 1600°C over 55h. Optical absorption and emission characteristics of Er3+ ions in the calcined Er3NbO7 powder were investigated and discussed compared with ErNbO4 phosphor and a Z-cut congruent Er (2mol%):LiNbO3 single crystal. The absorption and emission studies show that, due to different crystal structures, the spectroscopic properties of these niobates have some differences in spectral shape, peak position, and relative intensity, especially at 1.5μm. The most obvious spectral feature of the Er3NbO7 is that the spectral structure of band instead of peak is observed in its absorption or emission spectrum due to the existence of local structural disorder and multiple Er3+ sites. The Er3NbO4 shows stronger upconversion emission than the single crystal but weaker than the ErNbO4. Experimental results show that energy transfer upconversion and/or excited state absorption play a dominant role in the upconversion emissions, and, at higher pump level (>200mW), the thermal effect becomes significant and results in drop of the upconversion intensity. The 1.5μm lifetimes of Er3+ ion in the Er3NbO7, ErNbO4 phosphor, and in the Er:LiNbO3 crystal are measured to be ∼5.3, 2.0, and 2.4ms, respectively. In combination with the measured Raman spectra, the quantum efficiency, multiphonon nonradiative decay rate, and theoretical radiative lifetime of the 1.5μm emission of the two powder materials are expected. The differences in upconversion intensity and measured 1.5μm lifetime between the three materials are explained qualitatively. [Copyright &y& Elsevier]

A theoretical study has been performed on 1.76 μm on-chip amplification characteristics of Tm3+ in a rib waveguide of LiNbO 3 on insulator (Tm:LNOI) under 795 nm wavelength pumping. Steady-state rate equations and propagation equations of signal and pump waves are established on the basis of a three-level model of Tm3+ system with the cross relaxation process 3H 4 →3F 4 : 3H 6 →3F 4 included. The validity of the three-level model is demonstrated by referencing previously reported experiment result of Er3+-doped LNOI waveguide amplifier and by examining the effect of Tm3+ blue upconversion emissions on the 1.76 μm amplification. Besides the relations of signal gain to propagation length, launched pump power and input signal power, the effects of waveguide cross-section geometry and Tm3+ concentration on the gain characteristics are also studied. The results show that the waveguide cross-section geometry affects definitely the gain performance via its effect on mode field. The Tm3+ concentration affects the signal gain also via its effect on the 3H 4 →3F 4 : 3H 6 →3F 4 cross relaxation coefficient, besides the conventional effect that higher active ion concentration yields larger signal gain. A comparison with conventional Ti4+(Zn2+)-diffused Tm3+-doped LN [Ti(Zn):Tm:LN] waveguide shows that the Tm:LNOI waveguide has much better gain performance than the Ti(Zn):Tm:LN waveguide, including much stronger pump power and propagation distance dependences of signal gain, much higher signal gain and much lower threshold pump power. These features are associated with significantly increased Tm3+ population inversion extent due to ultra-compact mode field and larger overlapping factor of mode field and Tm3+ population profiles in the Tm:LNOI waveguide. • 1.8 μm amplification in Tm:LNOI waveguide is simulated based on three-level model. • Quantitative relations of signal gain to controllable parameters are established. • Tm:LNOI amplifier is more efficient than Ti(Zn):Tm:LN due to ultra-compact mode. • Waveguide cross-section geometry affects definitely gain via its effect on mode field. • Tm3+ concentration affects gain via its effect on cross relaxation process. [ABSTRACT FROM AUTHOR]

Abstract Visible and infrared absorption and emission spectra of Er3+-doped strontium gadolinium gallate (SrGdGa 3 O 7) single-crystal were measured at room temperature. From the measured fluorescence spectra, the Er3+ emission cross section spectra were calculated at first. Then, by utilizing McCumber relation, the absorption cross section spectra were further calculated. In parallel, the absorption cross section spectra were also calculated from the measured absorption spectra of the crystal, and compared with those spectra calculated from the McCumber relation. The comparison shows that the absorption cross section spectra obtained using the McCumber relation are in reasonable agreement with those deduced from the measured absorption spectrum. Graphical abstract Visible, near-infrared, and mid-infrared emission and absorption cross section spectra of Er3+ in SrGdGa 3 O 7 single-crystal have been calibrated from measured fluorescence spectra using the McCumber theory. The absorption cross-section spectrum was also calibrated from the measured absorption spectrum. Comparison shows that the absorption cross section spectra calibrated from the McCumber theory are reasonably consistent with those from the absorption spectrum. Present work presents complete cross section knowledge of the studied crystal. fx1 [ABSTRACT FROM AUTHOR]

Abstract Under 980 nm wavelength excitation, 530 and 550 nm green upconversion emission spectra of erbium-doped gadolinium gallium garnet single-crystal were measured in the temperature range of 298–423 K for ratiometric thermometry based on fluorescence intensity ratio (FIR). The crystal shows strong emission intensity, highly efficient ratiometric thermometric performance, as well as thermally stable emission spectral structure, it is thus a promising luminescent material for ratiometric thermometry. A multiple ratiometric thermometry is proposed and demonstrated in comparison with the usually adopted ratiometric thermometry based on integrated emission intensity. The multiple ratiometric thermometry considers six FIRs involving two component peaks of the 530 nm emission band and three component peaks of the 550 nm emission band, which result from an electronic transition from one Stark sublevel of the 2H 11/2 or 4S 3/2 state to another of the ground state 4I 15/2 of Er3+. All the six FIR schemes show highly efficient sensing performances with slightly different temperature characteristics. The temperature is overall determined by the six FIR schemes, largely increasing the reliability of temperature measurement. Graphical abstract We have studied ratiometric thermometry based on six fluorescence intensity ratios (FIR) involving two component peaks of 530 nm emission band and three component peaks of 550 nm emission band of erbium-doped gadolinium gallium garnet single-crystal. All the six EIR schemes display higher, slightly different relative sensitivities and thermal resolutions. The temperature is overall and reliably determined by the six EIR schemes. In addition, the crystal shows strong green upconversion emissions and thermally stable spectral structure, it is thus a promising material for the ratiometric thermometry. The multiple ratiometric thermometry based on the material has highly efficient performance, and is thus promising for reliable temperature detection in electromagnetically and/or thermally harsh environments and some industrial processes. fx1 [ABSTRACT FROM AUTHOR]

Temperature characteristics of 980-nm-upconverted green 530 and 550 nm fluorescence of Er 3+ -doped SrGdGa 3 O 7 single crystal have been studied for temperature sensing purposes. To achieve that, a simple experimental setup has been developed that consists of a 980 nm laser diode, two interference filters, two Si-photocells and two multimeters, while without use of monochromator or focusing lens for fluorescence collection. The study shows that the Er 3+ -doped SrGdGa 3 O 7 crystal displays strong green emission intensity (hence good signal-to-noise ratio) and high temperature sensitivity of fluorescence intensity ratio of the 530 and 550 nm emissions, which is (5.6–104.0) × 10 −3 K −1 in the considered temperature range 100–430 K, depending on the temperature. In addition, the experiments were repeated using a spectrometer and consistent results of temperature characteristics were obtained. Present study shows that the Er 3+ -doped SrGdGa 3 O 7 crystal is a promising host material for optical temperature sensing. [ABSTRACT FROM AUTHOR]

Er 3+ /Tm 3+ -codoped LiNbO 3 crystal was prepared by co-diffusion of stacked Er and Tm metal films coated onto surface of off-congruent, Li-deficient LiNbO 3 substrate produced by Li-poor vapor transport equilibration technique. The crystalline phase on the diffused surface was analyzed by X-ray single-crystal diffraction. The Er 3+ and Tm 3+ profile characteristics were studied by secondary ion mass spectrometry. The emission spectra were measured under the 980 or 795 nm wavelength excitation, and the emission and absorption cross section spectra were calculated based upon McCumber theory. The lifetimes of some emissions were measured. The results show that the Er 3+ and Tm 3+ ions presence is in the form of LiNbO 3 phase. Both ions obey to Gaussian profile with a diffusion depth 21.5 μm. In the codoping case, both ions keep their respective spectroscopic features of only doping case and do not affect each other. The codoping enables to combine the wavelength emissions of both ions and the resultant emission band in the telecommunication window around 1.5 μm is as wide as 150 nm, providing the possibility of S+C+L broadband amplification by employing commercial 980 and 795 nm laser diodes as the pump sources. The Er 3+ /Tm 3+ -codoped LN is a promising host material for integrated optics. [ABSTRACT FROM AUTHOR]

We demonstrate the applicability of a ratiometric luminescence thermometer to microelectronic components. The thermometer, which consists of a 980 nm laser diode, two optical filters, two photocells and two multimeters, works on the basis of thermal effect on luminescence intensity ratio of 980-nm-upconverted 530 and 550 nm emissions of micron-sized Er3+/Yb3+-codoped NaGd(WO 4) 2 crystalline phosphor. The applicability is demonstrated by using it to monitor in realtime the temperature of an integrated circuit chip on a printed circuit panel (PCB) in operation. In parallel, the temperature was also measured independently using an infrared thermometer. A comparison shows that the temperature measured by the luminescence thermometer can be considered as identical to that measured by the infrared one within error. The consistency of the result from the luminescence thermometer with that from the infrared one, together with previously reported result that the NaGd(WO 4) 2 phosphor is an excellent insulator with a resistivity of 2.0 × 1011 Ω · m at 330 K, verifies the applicability of the luminescence thermometer to microelectronics, and the thermometer has a measurement error of 2 K. • Ratiometric fluorescence thermometer is applied to microelectronic components. • Er/Yb:NaGd(WO 4) 2 phosphor adopted has a high resistivity of 6.0 × 1012 Ω · m at 328 K. • The thermometer is used to monitor temperature of an integrated circuit on a PCB. • Results measured by fluorescence and infrared thermometers are thought as same. • The agreement of results verifies applicability and the measurement error is 2 K. [ABSTRACT FROM AUTHOR]

Validity of Judd-Ofelt spectroscopy based on measured diffuse reflectance spectrum and fluorescence lifetime of a purely radiative electronic transition of rare-earth-ion in a powder material has been demonstrated. Two representative powder samples of Er3+-doped LiNbO 3 and Er3+/Yb3+-codoped NaYF 4 , which have considerably different phonon energies, 880 and 380 cm−1, respectively, have been exemplified to demonstrate the validity. First, diffuse reflectance spectrum was measured for each powder sample and relative absorption spectrum was calibrated from it using Kubelka-Munk relation. Second, fluorescence lifetime of purely radiative 1.5 μm emission of Er3+ was measured and absolute absorption cross-section spectrum was calibrated on the basis of the assumption that the measured 1.5 μm fluorescence lifetime equals the radiative lifetime. Finally, the Judd-Ofelt parameters Ω t (t = 2, 4, 6) are calculated on the basis of the absolute absorption cross-section spectrum. For comparison, Judd-Ofelt analysis was also performed on the Er3+-doped LiNbO 3 single-crystal on the basis of the absorption spectrum obtained from Beer-Lambert law. The Ω t result of Er3+-doped LiNbO 3 powder sample is compared with that of single-crystal state. The comparison shows that the Ω t result of the powder sample can be considered as the same as that of the single-crystal state within the error, confirming the validity of the method. The study on the Er3+/Yb3+-codoped NaYF 4 microcrystal powder allows us to reach the same conclusion. • A method for Judd-Ofelt (J-O) analysis of a phosphor material is validated. • The method is based on diffuse reflectance spectrum and fluorescence lifetime. • It is validated by comparing J-O results of Er:LiNbO 3 powder and single crystal. • And by comparing the results of Er/Yb:NaYF 4 powder with those reported earlier. • Results of powder and single-crystal states are same, validating thus the method. [ABSTRACT FROM AUTHOR]

Er3+/Yb3+-codoped CaIn 2 O 4 nano-fibers with good morphology were synthesized by electrospinning technique. X-ray diffraction was performed on the synthesized phosphor of nano-fibers to confirm that the CaIn 2 O 4 crystalline phase is dominant in it. The morphology of the nano-fibers was characterized by scanning electron microscopy. Optimal power supply voltage and thickener concentration for the synthesis were obtained. Er3+ 980-nm-upconverted emission characteristics of the nano-fibers were investigated. The results show that two-photon process is the dominant mechanism for the upconversion emissions. The nano-fibers doped with 5 mol% Er3+ display the strongest upconversion fluorescence. Temperature characteristics of the green 530 and 550 nm upconversion fluorescence of the nano-fibers were also studied for thermometry purposes. The results reveal that the nano-fibers show thermally stable spectral structure and the ones doped with 5 mol% Er3+ display the highest thermal sensitivity of green fluorescence intensity ratio. We conclude that there exists an optimal Er3+ concentration of 5 mol%, and the CaIn 2 O 4 nano-fibers doped with this optimal Er3+ concentration display some spectroscopic properties favorable for ratiometric thermometry in the high-temperature regime. • Er3+/Yb3+-codoped CaIn 2 O 4 nano-fibers were synthesized by electrospinning. • There exists optimal working voltage 18 kV and thickener concentration 10 wt%. • There is an optimal Er3+ concentration 5 mol% in case of 5 mol% Yb3+ codoping. • Er3+(5mol%)/Yb3+(5mol%):CaIn 2 O 4 shows efficient thermal sensing performance. • It is a promising material for nano-thermometry in high-temperature regime. [ABSTRACT FROM AUTHOR]