# Preparation of Lithium–Cesium Co-Doped Tungsten Oxide by Low-Temperature Hydrothermal Method

## TL;DR

A new low-temperature method creates a tungsten oxide material that can block heat while letting visible light through, useful for energy-efficient smart windows.

## Contribution

A low-temperature hydrothermal synthesis method for Li–Cs co-doped tungsten oxide with enhanced near-infrared absorption and visible transparency.

## Key findings

- The material has a hexagonal structure with Li+-induced lattice expansion.
- Oxygen vacancies correlate with W5+ content, enhancing near-infrared absorption.
- The material shows excellent visible light transmission and heat shielding properties.

## Abstract

Buildings consume 40% of global energy, over half of which is used for cooling and heating. Tungsten bronze (MxWO3) holds promise for smart windows due to its ability to block near-infrared (NIR) heat radiation while maintaining visible light transmittance. However, conventional high-temperature synthesis is energy intensive. Here, we develop a low-temperature hydrothermal method (170 °C) to prepare Li and Cs co-doped tungsten oxide using WCl6, LiF, and CsOH·H2O as precursors, with acetic acid as a crystallographic modulator. The material exhibits a hexagonal structure (P63/mcm) and Li+-induced lattice expansion (0.34 nm spacing). Combined XPS and ICP-OES analyses confirm the chemical composition as Cs0.31Li0.09WO3 and reveal a positive correlation between the W5+ content (15.76%) and oxygen vacancy concentration, which is identified as the key factor enhancing the NIR absorption. The material demonstrates excellent visible light transmission and NIR shielding properties. Our work provides a more energy-efficient and sustainable pathway for the production of smart window materials.