Holistic Assessment of NIR-Emitting Nd³⁺-Activated Phosphate Glasses: A Structure–Property Relationship Study

Abstract

Near-infrared (NIR)-emitting phosphate glasses containing Nd 3+ ions are attractive for applications in laser materials and solar spectral converters. The composition− structure−property relation in this type of glass system is thus of interest from fundamental and applied perspectives. In this work, Nd 3+ -containing glasses were made by melting with 50P 2 O 5 -(50 − x)BaO-xNd 2 O 3 (x = 0, 0.5, 1.0, 2.0, 3.0, 4.0 mol %) nominal compositions and studied comprehensively by density and related physical properties, X-ray diffraction (XRD), Raman spectroscopy, O 1s X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), dilatometry, ultraviolet−visible (UV−vis)−NIR optical absorption, and photoluminescence (PL) spectroscopy with decay dynamics assessment. The densities and molar volumes of the Nd 3+ -containing glasses generally increased with Nd 2 O 3 concentration also resulting in shorter Nd 3+ −Nd 3+ distances. XRD supported the amorphous nature of the glasses, whereas the Raman spectra evolution was indicative of glass depolymerization being induced by Nd 3+ ions. Oxygen (1s) and phosphorus (2p) analysis by XPS for the glass with 4.0 mol % Nd 2 O 3 agreed with the increase in nonbridging oxygens relative to the undoped host. DSC results showed that the glass transition temperatures increased with Nd 3+ concentration, with the glasses also displaying a decreased tendency toward crystallization. Dilatometry showed trends of increasing softening temperatures and decreasing thermal expansion coefficients with increasing Nd 2 O 3 content. A glass strengthening/tightening effect was then indicated to be induced by Nd 3+ with higher field strength compared to Ba 2+ ions. The UV−vis−NIR absorption by Nd 3+ ions increased consistently with Nd 3+ concentration. The UV−vis absorption edges of the Nd-containing glasses were also analyzed via Tauc and Urbach plots for comparison with the undoped host. Concerning the PL behavior, the Nd 3+ NIR emission intensity was highest for 1.0 mol % Nd 2 O 3 and decreased thereafter. The decay kinetics of the 4 F 3/2 emitting state in Nd 3+ ions analyzed revealed decreasing lifetimes where the decay rate analysis pointed to the prevalence of ion−ion excitation migration leading to PL quenching at high Nd 3+ concentrations.

Physical, Thermal, and Optical Properties of Mn2+ and Nd3+ Containing Barium Phosphate Glasses

“…Moreover, the intercept of 660 °C coincides with the T x value measured for the 2Mn glass (Table ). The increasing T x behavior characterizing thermal stability improvements also concurs with the reported for the singly Nd-doped barium phosphate glasses and Gd-loaded calcium phosphate glasses . The trend for the peak crystallization temperatures as well as the Δ T = T x – T g thermal stability parameter are also noticed to increase consistently for the 05-2NdMn glasses in Table .…”

“…The trend for the peak crystallization temperatures as well as the Δ T = T x – T g thermal stability parameter are also noticed to increase consistently for the 05-2NdMn glasses in Table . Thermal property changes such as these have been interpreted in terms of the high ionic field strength of the lanthanide ions substituting other cations with lower field strength. ,, Herein, we notice consistency with the report for the singly Nd-doped glasses concerning this argument. This is because exchanging Ba 2+ with Nd 3+ cations in the 05-2NdMn glasses is indicated to lead to a bond-strengthening effect and overall enhanced glass stability with increasing Nd 3+ concentration.…”

“…Figure shows the powder XRD patterns obtained for the different glasses (the photograph in the inset shows samples of the different glasses as slabs). The diffractograms show humps toward small 2θ values, which characterize the long-range structural disorder . Despite some intensity fluctuations seen with the broad features, the diffractograms do not show discrete crystallization peaks, thus supporting the noncrystalline nature of the glasses.…”

“…The obtained intercept of 497 °C was close to the measured T g for the 2Mn glass of 495 °C and coincided with the BP glass T g (Table ). Rising T g values were similarly seen with Nd 2 O 3 , replacing BaO in the 50P 2 O 5 –(50 – x )BaO– x Nd 2 O 3 (0 ≤ x ≤ 4 mol %) glass system . Such outcome is indicative of a glass strengthening effect induced by Nd 3+ ions and was similarly noticed by Wang et al, with increasing Gd 3+ content in calcium phosphate glasses with 50P 2 O 5 –(50 – x )CaO– x Gd 2 O 3 (0 ≤ x ≤ 6 mol %) compositions.…”

“…Comparing the results of the 2Mn glass in Table with the 2Nd as a reference also shows that the neodymium has a greater impact than manganese. For comparison, we may consider the ionic radii reported by Shannon of 0.83 and 0.983 Å for Mn 2+ and Nd 3+ cations, respectively, for anticipated coordination numbers of six. , The ionic field strengths ( F ) may be calculated with the common formula F = Z R 2 where R is the ionic radius and Z is the cation charge . The resulting F values are 2.903 and 3.105 Å –2 for Mn 2+ and Nd 3+ , respectively.…”