Luminescent materials based on organic salts pyrolyzed at the silica surface

Abstract

Recently, specific carbon-based nanomaterials (quantum dots, CDs) became highly attractive due to their low toxicity, good biocompatibility, chemical inertness, high photostability and fluorescence. Doping with some heteroatoms was found to be an effective approach to improve their luminescence. Besides, using the surface of silica as a support might facilitate the nanodots formation and expand the application area of carbon-silica composites. Recent advancements in synthesis of luminescent silica/CDs composites revealed great potential of such systems in bioimaging, sensor, as well as in solid-state lightning applications. Most of the synthetic methods are still relatively complex and costly. Here, the simple and inexpensive route to produce luminescent silica-based nanomaterials was used. The aim of this work was to study the luminescent properties of the materials obtained by pyrolysis of citric acid ureates at the nanosilica surface. Fumed silica was used as a support material. The salts with various ratios of citric acid and urea were obtained either in aqueous or alcohol solution, and they were further deposited on silica surface. The resulting material was then heat treated at the temperature of up to 270 °C, and the absorption and photoluminescence spectra for the samples obtained were collected and analyzed. The results have shown that irrespective of the solvent used, both dried and pyrolyzed samples possess the luminescent properties, with quantum yield of photoluminescence being within 7-11 %. The change of the citric acid-to-urea ratio in aqueous solution within 1:(1÷3) doesn't affect the luminescent properties of dried samples, but further pyrolysis at 270 °C reduces the photoluminescence intensity. The solvent change to ethanol has an ambiguous influence on the luminescent properties of dried silica samples with different citric acid-to-urea ratio applied, however, further thermal treatment at 270 °C results in the formation of the materials with almost the same luminescence properties. Within the citric acid-to-urea ratios and the solvents used, as well as the heat treatment regimes applied, the variant with the 1:1 salt in the alcohol solution applied to the silica surface with further drying and heat treatment at 270 °C was found to be the most suitable.

Luminescent Sol-Gel Glasses from Silicate–Citrate–(Thio)Ureate Precursors

“…Besides, it has been shown that silica gel glasses produced from silicate carboxylate precursors exhibit high PL characteristics [13]. Recent advancements in synthesis and analysis of silica/CDs composites revealed great potential of such systems in bioimaging, sensor, as well as solid-state lighting applications, and depending on the synthesis methods and the precursors used, it is possible already to achieve the PL QY from typically 7-14 up to 60% [14][15][16][17][18][19][20][21][22]. Table 2 gives the PL characteristics of some carbon-containing silica-based materials synthesized using various methods.…”

“…Table 2 gives the PL characteristics of some carbon-containing silica-based materials synthesized using various methods. -Pyrolysis of citric acid (thio)ureates at the fumed silica surface 7-11 [22] Most of the synthetic methods are still relatively complex and costly or the materials produced possess relatively low PL QY. In [22], the simple and inexpensive route to produce luminescent silica-based nanomaterials was used: citric acid ureates were deposited from aqueous or ethanol solutions onto fumed silica surface.…”

“…-Pyrolysis of citric acid (thio)ureates at the fumed silica surface 7-11 [22] Most of the synthetic methods are still relatively complex and costly or the materials produced possess relatively low PL QY. In [22], the simple and inexpensive route to produce luminescent silica-based nanomaterials was used: citric acid ureates were deposited from aqueous or ethanol solutions onto fumed silica surface. After drying and further thermal treatment at the temperature of up to 270 • C, such materials were found to demonstrate fluorescent properties, however, PL QY was quite low (within 7-11%).…”