Luminescence of Natural $\alpha$-Quartz Crystal with Aluminum, Alkali and Noble Ions Impurities

TL;DR

This study investigates the luminescence properties of natural and synthetic α-quartz crystals doped with aluminum, alkali, and noble ions, revealing defect-related emission characteristics and thermal quenching behaviors.

Contribution

It provides new insights into the luminescence mechanisms of α-quartz doped with various impurities, including the effects of noble and alkali ions on emission spectra and thermal stability.

Findings

Main blue photoluminescence band at ~400 nm linked to aluminum-alkali defect centers

Distinct luminescence bands for silver (~260 nm) and copper (~360 nm) ions at low temperatures

Thermal quenching energies and time constants characterized for different impurity-related emissions

Abstract

Photoluminescence and thermally stimulated luminescence of synthetic and natural (morion and smoky) $\alpha$-quartz crystals doped with aluminum and alkali ions were studied. The photoluminescence spectrum is characterized with the main blue band around 400 nm (~ 3.1 eV). The corresponding luminescence center is based on a defect containing aluminum and alkali as compensators in natural and synthetic quartz crystals. Photoluminescence can be detected at high temperatures above 700 K. The thermal quenching activation energy is 0.15 eV and the frequency factor is 3 10$^7$ s$^{-1}$. In the samples with silver ions the main luminescence band is located at ~ 260 nm (~ 4.7 eV) with a time constant of ~ 37 $\mu$s at 80 K, and in the samples with copper ions the PL band is at ~ 360 nm (~ 3.4 eV) with a time constant ~ 50 {\mu}s at 80 K. For luminescence associated with silver the energy of thermal quenching is 0.7 eV with a frequency coefficient of 1 10$^{14}$ s$^{-1}$, and for the luminescence related to copper, these parameters are 0.55 eV and 10$^{14}$ s$^{-1}$. The differences in intra-center luminescence properties of the same defect containing alkali ions or noble ions are based on differences in electronic transitions. In the case of alkali ions the charge transfer transitions between oxygen and alkali ions. In the case of noble ions absorption-luminescence corresponds to intra ion transitions. Radiation properties are related to trapping of an electron on one valence ion. Created atom moves out of aluminum containing defect. The hole remains on aluminum-oxygen defect. Thermally stimulated luminescence is related to release of atom, it diffusion to aluminum defect with the hole on oxygen and following radiative recombination.