Smartphone‐Based Luminescent Thermometry via Temperature‐Sensitive Delayed Fluorescence from Gd₂O₂S:Eu³⁺

Abstract

Thermal images generated from infrared radiation are useful for monitoring many processes; however, infrared cameras are orders of magnitude more expensive than their visible counterparts. Methods that allow visible cameras to capture thermal images are therefore of interest. In this contribution, thermal images of a surface coated with an inexpensive inorganic micropowder phosphor are generated from the analysis of a video taken with a smartphone camera. The phosphor is designed to have a temperature‐dependent emission lifetime that is long enough to be determined from the analysis of a 30 frames‐per‐second video recording. This proof‐of‐principle work allows temperatures in the 270–320 K range to be accurately determined with a precision better than 2 K, even in the presence of bright background illuminance up to 1500 lm m−2. In the broader context, this inspires further development of phosphors to bring time‐resolved sensing techniques into lifetime long enough ranges to allow smartphone‐based detection.

Dual-color dynamic anti-counterfeiting labels with persistent emission after visible excitation allowing smartphone authentication

“…The bulky and expensive equipment needed to image of such nano- to micro-second lifetimes can be avoided by shifting the lifetimes of the labels to the 100 ms to 10 s range 25 . The upper limit on lifetime here is imposed to allow sufficiently rapid authentication, limiting the charging time and video recording time such that authentication can be completed within around 15–20 s. Such extension in the PL lifetime would allow the use of a video captured with a standard camera, such as those in smartphones, to characterize the lifetimes and provide a series of images at different lifetimes 25 – 27 . Several phosphors exhibiting persistent color change have been explored, but, to date, tailoring lifetimes to create a materials palette optimized for smartphone excitation and detection has not been demonstrated.…”

Strong sensitivity enhancement in lifetime-based luminescence thermometry by co-doping of SrTiO3:Mn4+ nanocrystals with trivalent lanthanide ions

“…5 Unfortunately, in this case, the commonly obtained thermometer sensitivities to temperature changes are much lower than in the case of the luminescence intensity ratio counterparts. 5,[16][17][18]31,32 Therefore, extensive research is ongoing to develop new phosphors and/or to thermally activate different physical processes taking place in them to improve the sensitivity of lifetime-based luminescent thermometers. Recently, it has been shown that the SrTiO 3 :Mn 4+ nanocrystals show favourable thermometric properties not only in the LIR approach but also in the lifetime-based approach.…”

mOptical Sensing for the Internet of Things: A Smartphone‐Controlled Platform for Temperature Monitoring

“…[ 42 ] Figure a (and Table S2, Supporting Information) shows examples of the largest S r values ( S m ) reported for ratiometric (hollow symbols) luminescent thermometers with an operating range compatible with m Optical sensing and for smartphone‐based luminescence thermometry (solid symbols). [ 46,55,59,66–89 ] The S r values for primary luminescent thermometers are shown in Figure 3b. [ 43,53,58–64 ] Noticeable, only one example refers to smartphone‐based luminescence thermometry, and presents the largest S r value.…”

“…This approach includes a smartphone and although the analyses and excitation are externally provided, it is an important step toward m Optical sensing for IoT, as smartphones are widely available and easily accessible equipment for science and engineering to use. [ 83 ]…”