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This research article reports the non-contact optical thermometric study using the UC emission intensity ratio of thermally and non-thermally coupled levels. Tm3+/Er3+/Yb3+ codoped TeO2-WO3-Bi2O3 (TWBi) glass have been synthesized using melt-quenching technique. After analyzing the optical absorption and UC emission spectra at room temperature, the temperature-dependent study of UC emission spectra has been performed in the 303–523 K range. First, the optical temperature sensing using the luminescence intensity ratio of thermally coupled levels of Er3+ ion has been studied. The maximum value of absolute and relative sensitivities has been found to be ∼0.0088 K−1 at 483 K and ∼0.0120 K−1 at 303 K, respectively. Furthermore, the luminescence intensity ratio approach has been employed to study non-contact temperature sensing in non-thermally coupled levels. While employing the ratiometric approach involving non-thermally coupled levels, a simultaneous improvement in absolute and relative sensitivities has been witnessed. There, the maximum value of absolute and relative sensitivities has been found as high as ∼0.7143 K−1 at 523 K and ∼0.0249 K−1 at 483 K, respectively. It has been found that the relative sensitivity in the case of non-thermally coupled levels (NTCLs) clearly dominates the relative sensitivity of TCLs.

Strong up conversion (UC) luminescence at 527, 550, and 662 nm is compared under an excitation of 980 nm in single doped (Er3+), co-doped (Er3+/Yb3+), and (Er3+/Yb3+/W6+) tri-doped bismuth titanate (Bi4Ti3O12). For the co-doped system, the frequency (UC) emission intensity due to Er3+ ions is enhanced significantly in the green bands due to the efficient energy transfer from Yb3+ to Er3+ ions. Further increase in the emission intensity is seen with non-luminescent W6+ ions in the tri-doped system due to the modification in the local crystal field around the Er3+ ions, and is evidenced through a gradual change in the crystal structure of the host lattice with increasing W6+ content. The observed changes in the fluorescence lifetime and the associated energy transfer mechanisms are discussed. A progressive reduction of the lifetime of the 4S3/2 levels of Er3+ ions from 72 to 58.7 μs with the introduction of Yb3+ and W6+ dopant increases the transition probability and enhances the UC emission intensity. The ...

The authors in this manuscript present the results on synthesis of Er3+/Yb3+ codoped La2O3 upconverting phosphor and its demonstration on the development of latent fingermarks on the surfaces of semi-porous and non-porous objects. The samples were synthesized via combustion using urea as a reducing agent and chemical precipitation methods. The annealed samples showed enough intense green emission in the 520–550 nm range on 980 nm excitation. Excellent emission property of the samples in the green region showed an advantage to use it in latent fingermarks detection. A dry powder dusting technique is used to develop latent fingermarks and the results are compared. The studies reflected the superiority of upconversion phosphor materials for the detection of latent fingermarks over the traditional downconversion luminescence methods.

The Er3+, Eu3+, and Yb3+ codoped Y2O3 phosphors have been synthesized by combustion synthesis process. For the structural information, the XRD analysis of the developed phosphor has been done. The frequency upconversion (UC) emissions in the codoped Y2O3 phosphor on excitation with 980 nm diode laser in the visible region have been performed and explained on the basis of excited state absorption and energy transfer process. The mechanism responsible in UC emissions was observed to involve two photon absorption and efficiency of the UC luminescence is significantly enhanced by introducing the Yb3+ ions. The tunability in colour of emitted radiation has been visualized by chromaticity diagram on increasing power of excitation source. The temperature sensing behaviour of developed phosphor material has been investigated using fluorescence intensity ratio technique.

CaZrO3 phosphors co-doped with Er3+ and Yb3+ ions have been prepared by the urea combustion route. The formation of the orthorhombic phase of CaZrO3 was confirmed by powder x-ray diffraction. The absorption in the 280–1800 nm region and excitation spectrum corresponding to the emission at 545 nm for CaZrO3:Er3+/CaZrO3:Er3+,Yb3+ phosphors have been recorded. Upon excitation at 978 nm, the material displays strong energy transfer upconversion emission in the green and red spectral regions. The upconversion emission of the CaZrO3:Er3+,Yb3+ co-doped material shows an increased red-to-green ratio, indicating cross relaxation between Er3+ ions.

Optical properties of a neodymium (Nd3+) doped glass having composition based on the (Ga2S3)–(GeS2) system are reported. Transition probabilities, radiative lifetimes, and branching ratios related to Nd3+ levels were determined. Frequency upconversion (UC) luminescence due to nonresonant excitation at 1064 nm was observed at ≈535, ≈600, and ≈670 nm. The dependence of the UC intensity on the laser intensity and on the Nd3+ concentration as well as the dynamics of the luminescence process were studied. The results indicate that two-photon absorption by isolated Nd3+ ions and energy transfer among pairs of Nd3+ ions contribute to the UC luminescence.

A frequency upconversion process in Pr3+ doped TeO2–ZnO glasses containing silver nanoparticles is studied under excitation with a nanosecond laser operating at 590 nm, in resonance with the H34→D12 transition. The excited Pr3+ ions exchange energy in the presence of the nanoparticles, originating efficient conversion from orange to blue. The enhancement in the intensity of the luminescence at ∼482 nm, corresponding to the P30→H34 transition, is due to the influence of the large local field on the Pr3+ ions, which are located near the metallic nanoparticles.

The infrared-to-visible upconversion (UC) in Tm3+-doped TeO2–PbO glass was investigated by exciting the samples with a Q-switched neodymium doped yttrium aluminum garnet laser operating at 1064nm. UC emission bands at ∼454, ∼482, and ∼518nm corresponding, respectively, to the transitions D21→F43, G41→H63, and D21→H53 were observed. Based on the dependence of the UC signals as a function of the Tm3+ concentration and excitation intensity, we concluded that the generation of the UC emissions involves excited state absorption and cross relaxation among Tm3+ ions.

Absorption and luminescence experiments were performed in thulium (Tm3+)-doped TeO2-PbO glass samples. Spectroscopic quantities such as transition probabilities, branching ratios, and radiative lifetimes related to the Tm3+ ions were determined using the Judd-Ofelt theory. Luminescence properties were studied by exciting the samples using a pulsed laser operating at 590 nm. Stokes luminescence centered at 792 nm and frequency upconversion (UC) to the blue (≈457 nm) were observed. The intensity and the time evolution of both emissions were studied for different concentrations of Tm3+ ions. The results indicate that the dipole-dipole interaction provides the most important contribution for energy transfer among the Tm3+ ions. The origin of the UC process is attributed to energy transfer among Tm3+ ions in pairs.

Optical properties of Pr3+ doped TeO2–PbO glass were investigated by resonant excitation of H43→D21 transition at ∼586nm. The decay time of D21 level, the energy transfer (ET) rates from the D21 level to other Pr3+ states, and the frequency upconversion process which leads to emission at 484nm (P03→H43 transition) were studied. The ET rates between Pr3+ ions were determined and their interaction was identified as due to dipole-dipole potential. A model used to describe the emission P03→H43 provided information on the dynamics of Pr3+ pair states. The upconversion ET rate was also determined.