Phonon Energy Of Host Research Articles

Improved thermally coupled levels based temperature sensing performance by engineering host phonon energy

Luminescence intensity ratio (LIR) based thermometers provide fast response, excellent accuracy and high spatial resolution. Temperature sensitivity is the most critical parameter for evaluating temperature measurement capability, and it is always interesting to develop novel methods to improve its sensitivity. In this work, we verify that the BaF2:Yb/Er NCs with lower phonon energy exhibits better temperature sensitivity than that of CaF2:Yb/Er NCs. The maximum relative temperature sensitivity of CaF2:Yb/Er NCs was calculated to be 0.596% K−1, while that of BaF2:Yb/Er NCs was calculated to be 0.779% K−1. Similar results were also observed through comparing the BaF2:Yb/Er@CaF2 and BaF2:Yb/Er@BaF2 core/shell NCs. Our results provide a novel method that engineering host phonon energy to improve the thermally coupled levels based temperature sensing performance.

Spectroscopic investigation of dysprosium doped BaF2 single crystals pertaining to the 3 µm mid-IR laser potential

We present the results of a comprehensive spectroscopic investigation pertaining to laser potential evaluation of the 3-micron Dy3+ mid-IR transition in the low-maximum phonon energy host barium fluoride (BaF2). This investigation involved absorption, fluorescence, and decay time measurements, recorded for a range of temperatures. Laser-relevant parameters such as absorption and stimulated-emission cross sections, quantum-efficiencies, and radiative lifetimes were determined for room temperature (300 K) and liquid nitrogen temperature. The peak stimulated emission cross section was found to be 0.45×10−20 cm2 at room temperature and 1.58×10−20 cm2 at 77 K. The gain cross sections, predictive of laser potential, were also derived. Finally, an examination of the nature of the non-radiative decay rates as a function of temperature was performed, showing the degree to which multi-phonon relaxation and other non-radiative pathways affect the overall fluorescence behavior.

Judd–Ofelt Parametrization from the Emission Spectrum of Pr3+ Doped Materials: Theory, Application Software, and Demonstration on Pr3+ Doped YF3 and LaF3

AbstractJudd–Ofelt (JO) theory explains the optical properties of trivalent lanthanides using only three intensity parameters. The JO parametrization is a complicated procedure of absorption spectra analysis, especially cumbersome for powders and non‐transparent materials. For the Pr3+ activated materials, the procedure is additionally complicated due to strong interaction of low‐lying Pr3+ 4f5d energy levels with the 4f levels. Here, the straightforward JO parametrization method that uses the emission spectrum and the excited state lifetime of the Pr3+ 3P0 level which does not require any fitting procedure are shown. In addition, the theory and software for calculations of JO parameters from Pr3+ emission are explained. The method requirements are low‐temperature photoluminescence measurements of Pr3+ introduced in low phonon energy hosts with a relatively high lying 4f5d energy level. The method is demonstrated on emissions of YF3:Pr3+ and LaF3:Pr3+ powders.

Improving Upconversion Photoluminescence of GdAlO3:Er3+, Yb3+ Phosphors via Ga3+, Lu3+ Doping

GdAlO3:Er3+, Yb3+ phosphors doped with Lu3+, Ga3+ ions were prepared via coprecipitation. The influences of substituting Ga3+ for Al3+ and substituting Lu3+ for Gd3+ on the structure and upconversion photoluminescence (UCPL) of the phosphors were studied. The experimental results show that the crystal textures did not change but the lattice parameters changed slightly via Lu3+, Ga3+ doping. This results in a decrease in the host phonon energy and a marked improvement in the green emission spectrum at 546nm. Moreover, the amounts of surface CO2, CO32-, and OH- species gradually decreased with Lu3+, Ga3+ doping. The combined effects led to an improvement in the UCPL efficiency with Ga3+, Lu3+ doping.

Color tuning dependence on cross-relaxation effect of Pr3+ activated yttrium germanate phosphor

Phosphors are important photoluminescence (PL) materials that are widely used in the lighting and display fields. The PL tricolor of phosphors is commonly obtained by doping different kinds of the emitters in phosphors. In this work, we first report the multicolor PL of Pr3+ single activated Y2GeO5 phosphor. Excited at 254 nm, the PL color of the phosphor can be tuned from red to yellow, green and even blue by changing the Pr3+ content. It reveals that this observation is due to the cross-relaxation effect of Pr3+ in a low phonon energy host. On the basis of this multicolor phosphor, a multicolor luminescent image is fabricated for anticounterfeiting application.

1.2 μm persistent luminescence of Ho3+ in LaAlO3 and LaGaO3 perovskites

Combination between electron traps and host phonon energy for Ho3+ persistent luminescence in perovskites.

Optical spectroscopy of holmium doped K2LaCl5

Spectroscopic results on the infrared emission properties of trivalent holmium (Ho3+) doped potassium lanthanum chloride (K2LaCl5) are presented. Using ~900nm excitation, Ho3+ doped K2LaCl5, which has a maximum phonon energy of 235cm−1, exhibited the infrared emissions at ~1660, ~1995, and ~3900nm at room temperature. The mid-infrared emission at 3900nm originated from the 5I5 → 5I6 transition of Ho3+ ions with an exponential decay time of ~7.8ms at room temperature. The fluorescence lifetimes were almost independent of temperature, indicating a negligibly small non-radiative decay rate for the 5I5 excited state, as predicted by the energy gap law for low phonon energy hosts. The Stark level energies of the lower 5IJ manifolds in Ho:K2LaCl5 were resolved from spectroscopic results performed at cryogenic temperatures. The transition line-strengths, radiative lifetimes, and fluorescence branching ratios were investigated by using the Judd-Ofelt method. In addition, the peak emission cross-section of the 5I5 → 5I6 transition was calculated to be 1.8 × 10–20cm2 at ~3890nm.

Quantitative Analysis of Energy Transfer and Origin of Quenching in Er(3+)/Ho(3+) Codoped Germanosilicate Glasses.

The energy transfer mechanism between Ho(3+) and Er(3+) ions has been investigated in germanosilicate glass excited by 980 nm laser diode. A rate equation model was developed to demonstrate the energy transfer from Er(3+) to Ho(3+) ions, quantitatively. Energy transfer efficiency from the Er(3+):(4)I13/2 to the Ho(3+):(5)I7 level can reach as high as 75%. Such a high efficiency was attributed to the excellent matching of the host phonon energy with the energy gap between Er(3+):(4)I13/2 and Ho(3+):(5)I7 levels. In addition, the energy transfer microparameter (CDA) from Er(3+):(4)I13/2 to Ho(3+):(5)I7 level was estimated to (4.16 ± 0.03) × 10(-40) cm(6)·s(-1) via the host-assisted spectral overlap function, coinciding with the CDA (2,88 ± 0.04) × 10(-40) cm(6)·s(-1) from decay analysis of the Er(3+):(4)I13/2 level which also indicated hopping migration-assisted energy transfer. Furthermore, the concentration quenching of Ho(3+):(5)I7 → (5)I8 transition was the dipole-dipole interaction in the diffusion-limited regime, and the quenching concentration of Ho(3+) reached 4.13 × 10(20) cm(-3).

Compositional-dependent europium-doped lead phosphate glasses and their spectroscopic properties

New multicomponent europium-doped lead phosphate based glasses with various PbO:P2O5 molar ratios were prepared and next studied using optical spectroscopy. Based on excitation and luminescence spectra measurements, some spectroscopic parameters like the phonon energy of the glass host and the fluorescence intensity ratio R of the 5D0→7F2 to 5D0→7F1 transition of Eu3+ ions were determined. Luminescence lifetimes (τm) for the 5D0 state of Eu3+ ions were also evaluated. Optical properties of Eu3+ ions have been investigated in lead phosphate based systems, in which PbO:P2O5 molar ratio were changed from 1:5 to 5:1 in glass composition. The value of the phonon energy of the host decreases with increasing PbO concentration. In addition, the spectral lines are shifted toward higher wavelengths. Non-monotonic dependence of fluorescence intensity ratio R (Eu3+) upon PbO:P2O5 content has been observed. Influence of PbO:P2O5 molar ratio on spectroscopic parameters for Eu3+ are presented and discussed.

Enhanced 1.8 μm emission in Yb3+/Tm3+ co-doped tellurite glass: Effects of Yb3+↔Tm3+ energy transfer and back transfer

The ~1.8μm emission characteristics of Tm3+ by a direct excitation and through an energy transfer process upon sensitization with Yb3+ ions in tellurite glass are reported. The spectroscopic properties of Tm3+ ions have been evaluated by applying Judd–Ofelt theory on the measured absorption spectrum. The obtained intensity parameters, Ω2=7.155×10−20cm2, Ω4=3.325×10−20cm2, Ω6=1.278×10−20cm2 are used to estimate the radiative properties of Tm3+ ions in the present glass host. A ~10 fold enhancement in the Tm3+ 1.8μm emission observed with 16 fold reduced emission of Yb3+ ions (1008nm) in co-doped sample on Yb3+ ions excitation illustrates the efficient energy transfer from Yb3+: 2F5/2→Tm3+: 3H5. The energy transfer process assisted by host phonon energy has been discussed by using relevant theoretical models and estimated the energy transfer micro-parameters. Effect of energy back transfer Tm3+→Yb3+ on NIR and upconversion emissions have been discussed. An efficient ~1.8μm with comparatively higher emission cross-section 1.115×10−20cm2 on account of reduced upconversion emissions has been achieved in the present tellurite glass.

Ultralow-threshold laser and blue shift cooperative luminescence in a Yb3+ doped silica microsphere

An experimental investigation on ultralow threshold laser and blue shift cooperative luminescence (CL) in a Yb3+ doped silica microsphere (YDSM) with continuous-wave 976 nm laser diode pumping is reported. The experimental results show that the YDSM emits laser oscillation with ultralow threshold of 2.62 μW, and the laser spectrum is modulated by the microsphere morphology characteristics. In addition, blue emission of YDSM is also observed with the increase of pump power, which is supposed to be generated by CL of excited Yb ion-pairs with the absorption of 976 nm photons and Si-O vibration phonons, and the process is explained with an energy level diagram. This property of the blue shift CL with phonons absorption in the Yb3+doped microcavity makes it attractive for the application of laser cooling based on anti-Stokes fluorescence emission, if the Yb3+doped microcavity made from with low phonon energy host materials.

Influence of bismuth on structural, elastic and spectroscopic properties of Nd3+ doped Zinc–Boro-Bismuthate glasses

The present investigation reports, influence of bismuth addition on structural, elastic and spectral properties of [(99.5−x) {4ZnO−3B2O3}−0.5Nd2O3−x Bi2O3 where x=0, 5, 10, 20, 30, 40, 50 and 60] glasses. The measured FTIR reflectance spectra facilitated a thorough insight of methodical modifications that are arising in the glass structure from borate (build by BO3 and BO4 units) to bismuthate (BiO3 and BiO6 units) network due to the increase of bismuth content ensuing with a steady decrease in host phonon energy (νph). The elastic properties estimated from measured longitudinal and shear ultrasonic velocities (UL and Us) demonstrated the reduction in network rigidity of glasses on Bi2O3 inclusion. The three phenomenological Judd–Ofelt intensity parameters (Ω2,4,6) were obtained from recorded absorption spectra of Nd3+ ions in these glasses and have been used to predict radiative properties as a function of variation in bismuth content. The reduced host phonon energy and high optical basicity effect due to Bi2O3 incorporation remarkably improved the Nd3+ luminescence properties such as emission intensity, quantum yield and emission cross-section. The quantum yield showed a strong increase from mere 16% in Zinc–Borate glass to almost 73% in 60mol% Bi2O3 containing glass. Similarly, the emission cross-section for Nd3+4F3/2→4I11/2 laser transition raised from 2.43×10−20cm2 to 3.95×10−20cm2 in studied concentration suggesting a strong improvement in Nd3+ laser spectroscopic properties in Zinc–Boro-Bismuthate glass. These materials may be promising for compact solid state infrared lasers.

Phonon assisted effective non-resonant energy transfer based 1 μm luminescence from Nd3+–Yb3+ codoped zinc–boro–bismuthate glasses

Phonon assisted non-resonant energy transfer from Nd3+→Yb3+ is reported in a new series of heavy metal oxide based zinc–boro–bismuthate glasses. An intense infrared emission at around 1μm from Yb3+ has been realized upon Nd3+ excitation, with a transfer efficiency reaching up to 87% for fairly low acceptor concentration of 1mol% Yb2O3. Such high energy transfer efficiency despite poor spectral overlap of donor’s emission with acceptor's absorption has been attributed to the excellent matching of host phonon energy with the energy difference among Nd3+ and Yb3+ excitation levels. From the host assisted spectral overlap function, the microscopic energy transfer parameter (CDA) for Nd3+→Yb3+ energy transfer in these glasses have been estimated and is found to be ∼3.6×10−39cm6s−1, which is in good agreement with the CDA value obtained from decay analysis of donor luminescence. The measured fluorescence decay curve showed excellent correlation with the theoretical fit simulated using hopping model suggesting the hopping migration assisted energy transfer. A comparison of the obtained results with other reported host systems has been presented using a performance parameter (ΦET) defining the ability of Nd3+→Yb3+ energy transfer per unit loss occurred due to Nd3+–Nd3+ self-quenching.

Study on Tb3+ containing high silica and low silica calcium aluminate glasses: Impact of optical basicity

Two series of glasses based on high silica (CAS) and low silica calcium aluminates (LSCA) have been investigated for their structural, optical and Tb3+ luminescence properties. The compositional modification reduces host phonon energy in LSCA glasses. Still, LSCA glasses exhibit Tb3+ green luminescence quenching, whereas no quenching observed in CAS glasses. Material property influence on this behaviour has been discussed with an insight into the redox state of active ions.

Spectroscopic study of neodymium doped potassium lead bromide for mid-infrared solid state lasers

We present spectroscopic results of the mid-infrared (MIR) emission (4I11/2→4I9/2) properties of neodymium (Nd) doped potassium lead bromide (KPb2Br5). Following optical excitation at either 0.808 or 0.89μm, Nd:KPb2Br5 showed a broad MIR emission band centered at 5.25μm with a bandwidth of 0.76μm at full width half maximum. For low concentration samples (5×1018cm−3), the emission lifetime was determined to be 43ms at room temperature and increased to 57ms at low temperature (15K). Based on the energy-gap law, non-radiative decay through multi-phonon relaxation is predicted to be negligibly small in this low phonon energy host material with ℏωmax=138cm−1. Therefore, the modest temperature dependence of the MIR lifetime is most likely due to the existence of non-radiative decay related to residual defects in the sample. The peak emission cross-section for the 4I11/2→4I9/2 transition was determined to be 0.65×10−20cm2. Some comparative results on Nd:KPb2Cl5 were also included in this study.

Broadband Er^3+ emission in highly nonlinear Bismuth modified Zinc-Borate glasses

Broadband NIR emission from Er3+ in highly nonlinear zinc-bismuth-borate glasses with full width at half maximum reaching up to 106 nm is reported. The glass compositional effects on thermal, structural, optical and spectroscopic properties have been explored in view of all-optical communication applications. The Zero Dispersion Wavelength of these glasses is found to be varying from 1.46 to 2.26μm. The observed enhancement in fluorescence intensity, lifetime and quantum efficiency of 4I13/2 → 4I15/2 transition with bismuth addition is attributed to reduced multiphonon relaxations with decreased host phonon energy. The gain profile covering C and L-bands of communication windows suggests their potentiality in broad-band amplification.

Efficient non-resonant energy transfer in Nd^3+-Yb^3+ codoped Ba-Al-metaphosphate glasses

An efficient Nd3+→Yb3+ energy transfer in a new series of alkali-free barium-alumino-metaphosphate glasses with a transfer efficiency reaching up to 95% has been reported here. It is due to the effective phonon assistance arising with the excellent matching of the present host phonon energy with the energy mismatch between Nd3+(4F3/2) and Yb3+(2F5/2) excited levels. The energy transfer microparameters for Nd3+→Yb3+ forward and back energy transfers are estimated from the spectral data analysis. A parameter, ΦET(=CDANd-Yb/CDANd-Nd), is proposed as a quantitative measure of sensitization ability per unit loss of the donor. The parameter is found to be highest for the presently reported barium-alumino-metaphosphate glasses.

Downconversion for the Er3+, Yb3+ couple in KPb2Cl5—A low-phonon frequency host

Downconversion of a single blue/green photon to two near-infrared photons offers a promising route to increase the efficiency of photovoltaic cells. Here we report on downconversion for the well-known upconversion couple (Er3+, Yb3+) doped into a host with low (∼200 cm−1) maximum phonon energy (KPb2Cl5). The intermediate energy level in both the upconversion and downconversion processes is the 4F7/2 level around 490 nm. While fast multi-phonon relaxation to the lower energy 2H11/2/4S3/2 levels is beneficial for upconversion, it prevents efficient downconversion. To reduce multi-phonon relaxation, a low-phonon energy host (KPb2Cl5) was doped with Er3+ and varying amounts of Yb3+ co-dopant. The results show that downconversion from the 4F7/2 level occurs, exciting two neighboring Yb3+ ions to the 2F5/2 level. The efficiency is however low due to multi-phonon relaxation from the 4F7/2 to the 4S3/2 level via the intermediate 2H11/2 level. Based on the results it is clear that efficient downconversion for the (Er3+, Yb3+) couple requires even lower phonon energy hosts (e.g. bromide host lattices). A Cl−–Yb3+ charge transfer absorption band is observed between 300 and 400 nm. Excitation in this band results in two broad emission bands centered around 430 and 700 nm at temperatures below 30 K, which are assigned to Cl−–Yb3+ charge transfer emission.

Laser cooling of Er3+-doped solids

We consider theoretically a mechanism for laser cooling in rare-earth-doped low-phonon materials based simultaneously on two cooling cycles: a traditional cooling cycle with an anti-Stokes fluorescence transition as well as an infrared-to-visible upconversion cycle, to overcome the self-termination effects in either anti-Stokes or upconversion cooling on its own. Our simulations, performed for erbium-doped potassium-lead chloride crystal ( Er 3+:KPl 2Cl 5) known to be an extremely low phonon energy host, uses two pump wavelengths corresponding to the long wavelength tails of the absorption spectra of the 4 I 15/2 → 4 I 13/2 and 4 I 15/2 → 4 I 9/2 transitions. The contribution of each pump source to the cooling process is comprehensively investigated. We show that, although the energy gap between 4 I 15/2 and 4 I 9/2 levels exceeds the energy gap between 4 I 15/2 and 4 I 13/2 levels and cooling process is more efficient with the cycle based on the 4 I 15/2 → 4 I 13/2 transition, the second cooling cycle based on the 4 I 15/2 → 4 I 9/2 transition can be used as a supplementary one.

Dependence of optical properties on the composition in Er 3+-doped xNaPO 3–(80 − x)TeO 2–10ZnO–10Na 2O glasses

Transparent and uniform tellurite–phosphate glasses were prepared and the reason why the substitution of NaPO 3 for P 2O 5 can eliminate the coloration of tellurite–phosphate was discussed. The result of TDA indicated that introducing NaPO 3 into tellurite glasses can improve thermal stability of glass hosts. The compositional dependence of absorption cross-sections of 4I 13/2, 4I 11/2 and 2H 11/2 level, emission cross-section of 4I 13/2 level, host phonon energy, up-conversion and 1.5 μm optical emission intensity as well as and quantum yield for 4I 13/2 level in PTEr glasses were investigated too. By analyzing obtained data, authors believe that tellurite–phosphate glasses can be used as potential host material for developing optical amplifiers.