Study on Upconversion and Thermal Properties of Tm3+/Yb3+ Co-Doped La₂O₃-Nb₂O₅-Ta₂O₅ Glasses

Spectroscopic Properties of Pr3+, Tm3+, and Ho3+ in Germanate-Based Glass Systems Modified by TiO2

In this paper, the effect of the GeO₂:TiO₂ molar ratio in glass composition on the spectroscopic properties of germanate glasses was systematically investigated. The visible luminescence bands associated with characteristic ¹D₂ → ³H₄ (red), ⁵S₂, ⁵F₄ → ⁵I₈ (green), and ¹D₂ → ³F₄ (blue) transitions of Pr³⁺, Ho³⁺, and Tm³⁺ ions in systems modified by TiO₂ were well observed, respectively. It was found that the luminescence intensity of glasses containing Pr³⁺ and Ho³⁺ ions increases, whereas, for Tm³⁺-doped systems, luminescence quenching with increasing content of TiO₂ was observed. Based on Commission Internationale de I'Eclairage (CIE) chromaticity coordinates (x, y) analysis, it was demonstrated that the value of chromaticity coordinates for all glasses depends on the GeO₂:TiO₂ molar ratio. The addition of TiO₂ to system compositions doped with Tm³⁺ ions shifts the (x, y) to the center of the CIE diagram. However, chromaticity coordinates evaluated for glasses containing Pr³⁺ ions move to a purer red color. Our results confirm that the spectroscopic properties of the studied glasses strongly depend on TiO₂ content. Moreover, it can be stated that germanate-based glass systems modified by TiO₂ can be used for optoelectronics in RGB technology as red (Pr³⁺), green (Ho³⁺), and blue (Tm³⁺) emitters.

Influence of Oxide Glass Modifiers on the Structural and Spectroscopic Properties of Phosphate Glasses for Visible and Near-Infrared Photonic Applications

The effect of oxide modifiers on multiple properties (structural and spectroscopic) of phosphate glasses with molar composition 60P₂O₅-(10-x)Ga₂O₃-30MO-xEu₂O₃ and 60P₂O₅-(10-y)Ga₂O₃-30MO-yEr₂O₃ (where M = Ca, Sr, Ba; x = 0, 0.5; y = 0, 1) were systematically examined and discussed. The local structure of systems was evidenced by the infrared (IR-ATR) and Raman spectroscopic techniques. The spectroscopic behaviors of the studied glass systems were determined based on analysis of recorded spectra (excitation and emission) as well as luminescence decay curves. Intense red and near-infrared emissions (1.5 μm) were observed for samples doped with Eu³⁺ and Er³⁺ ions, respectively. It was found that the value of fluorescence intensity ratio R/O related to ⁵D₀→⁷F₂ (red) and ⁵D₀→⁷F₁ (orange) transition of Eu³⁺ ions depends on the oxide modifiers MO in the glass host. However, no clear influence of glass modifiers on the luminescence linewidth (FWHM) was observed for phosphate systems doped with Er³⁺ ions. Moreover, the ⁵D₀ and ⁴I_13/2 luminescence lifetimes of Eu³⁺ and Er³⁺ ions increase with the increasing ionic radius of M²⁺ (M = Ca, Sr, Ba) in the host matrix. The obtained results suggest the applicability of the phosphate glasses with oxide modifiers as potential red and near-infrared photoluminescent materials in photonic devices.

Thermal Model and Countermeasures for Future Smart Glasses

The market for wearable devices such as smart watches and smart glasses continues to grow rapidly. Smart glasses are attracting particular attention because they offer convenient features such as hands-free augmented reality (AR). Since smart glasses directly touch the face and head, the device with high temperature has a detrimental effect on human physical health. This paper presents a thermal network model in a steady state condition and thermal countermeasure methods for thermal management of future smart glasses. It is accomplished by disassembling the state by wearing smart glasses into some parts, creating the equivalent thermal resistance circuit for each part, approximating heat-generating components such as integrated circuits (ICs) to simple physical structures, setting power consumption to the heat sources, and providing heat transfer coefficients of natural convection in air. The average temperature difference between the thermal network model and a commercial thermal solver is 0.9 °C when the maximum temperature is 62 °C. Results of an experiment using the model show that the temperature of the part near the ear that directly touches the skin can be reduced by 51.4% by distributing heat sources into both sides, 11.1% by placing higher heat-generating components farther from the ear, and 65.3% in comparison with all high conductivity materials by using a combination of low thermal conductivity materials for temples and temple tips and high conductivity materials for rims.