Monitoring decomposition of Eu³⁺ doped LaPO₄ nanocrystals in glass using Eu³⁺ as an optical probe for applications in temperature sensing

The methods to directly introduce crystals of known chemistry, size, and optical properties into a glass matrix are useful to circumvent some limitations related to the control of the growth of crystalline phases in glass-ceramics. The emission spectrum of LaPO₄:Eu³⁺ is characteristic for highly symmetrical coordination of Eu³⁺ and very distinct from the emission spectrum of Eu³⁺ in amorphous host, which allows for its application as an optical probe. Here, Eu³⁺ - doped LaPO₄ crystals were prepared using solid state reaction and added into various phosphate glass melt before quenching. From the changes in the micro-luminescence spectra, the decomposition occurs along with the diffusion of the Eu³⁺ ions into the glass confirming that the measurement of the micro-luminescence allows one to precisely track the crystal's decomposition inside the composite. It is demonstrated, for the first time to our knowledge, that the thermometric sensitivity of the Eu³⁺ ions can be enhanced by adding the LaPO₄:Eu³⁺ crystals into phosphate fluoride glasses due to special separation of the crystallites during the composite preparation and also to the reduction of the self-absorption of the ⁵D₁→⁷F₁ emission. The composite material is promising for applications in temperature sensing.