Our data

Invisible light in. Measured light out.

Measurements from the IMS lab in Princeton. One erbium-doped crystal, gadolinium oxysulfide (Gd₂O₂S:Er 6%), is driven by a bank of near-infrared laser diodes whose power and timing we program channel by channel. We record the blue, green and red light it gives back, millisecond by millisecond.

Gd₂O₂S:Er 6%785 – 1625 nm excitation30 ms · 300 ms · 3 s pulses50 – 260 mA laser drive
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Measured data plotted from IMS lab recordingsIllustration drawn by IMS to explain
The test rig

Six lasers, one crystal, one feedback loop.

Every measurement on this page comes from this setup. The controller can hold each laser steady or drive it with any waveform, so the crystal can be questioned with almost any mix of infrared light.

IllustrationIMS multi-laser excitation rigA programmable 8-channel current source drives six near-infrared laser diodes (808, 830, 900, 980, 1550 and 1625 nm). Gold mirrors steer the beams onto a near-infrared grating that combines them into one beam, focused onto a Gd2O2S:Er 6% sample on a glass slide. A 10x objective collects the visible emission, a visible grating splits it into colors, and the signal recorder logs blue, green and red light over time, closing the feedback loop.808 nm830 nm900 nm980 nm1550 nm1625 nmNIR gratingcombines all lasersGd₂O₂S:Er 6%sample on glass slide10× objectiveVIS gratingDetectorblue · green · redSIGNAL BACK TO RECORDER8-channel programmablecurrent source& signal recordersets each laser's power & timingUSBControl computerAFCloopDRIVE PROFILESsteady … or any waveformIllustration redrawn by IMS from the lab schematic · beam colors are false colors for invisible infrared
  1. 1
    ProgramAn 8-channel current source sets each laser diode's drive current: steady, pulsed or any waveform.
  2. 2
    CombineGold mirrors steer the 808 to 1625 nm beams onto a near-infrared grating that merges them into one beam.
  3. 3
    ExciteThe combined beam is focused onto Gd₂O₂S:Er 6% on a glass slide.
  4. 4
    CollectA 10× objective gathers the visible emission; a visible grating separates blue, green and red.
  5. 5
    Record and adjustThe recorder logs each color over time and feeds it back to the controller, closing the loop for the next run.
Measured data · luminescence traces

Change the light mix. Watch the crystal answer.

Each run blends seven near-infrared lasers in a set proportion, shown by the bars, and records blue, green and red emission at the same time. Choose a pulse length.

Measured dataBlue, green and red luminescence traces of Gd2O2S:Er 6% for 30 ms excitation, with the excitation laser mix from 785 to 1625 nm

30 ms excitation

Each laser mix is held for 30 ms, so you can see the light build up over the first milliseconds and fade after the lasers switch off.

Top left · blue
Top right · green
Bottom left · red
Bars · laser mix

Vertical axis: normalized luminescence. Successive traces are offset in time and height so they can be compared side by side. Bars: relative intensity of each laser (785, 808, 830, 905, 980, 1550, 1625 nm) in that run.

Three colors at once

One crystal, three channels.

Erbium gives off blue, green and red light together. Each color is recorded on its own, so a single reading carries three signals, not one.

The mix matters

The excitation is part of the code.

Each run uses a different blend of lasers. Which wavelengths, how strong and for how long are all choices the reader makes, and the crystal's answer depends on all three.

Rise, hold, fade

Timing is information.

The 30 ms traces show how the light builds and fades. IMS readers use timing as well as color; see U.S. Patent 11,922,265 on temporal authentication.

Measured data · green emission

Green light vs. laser power, one wavelength at a time.

Each surface follows green emission (arbitrary units) through a 60 ms window while the laser-diode drive current is stepped from 50 to 260 mA. Same crystal, three excitation wavelengths, plus an 808 nm control. The blue and red surfaces look similar. Click any panel to enlarge.

3D surface of green luminescence of Gd2O2S:Er 6% versus time and laser-diode current, 808 nm excitation
Measured dataScale to 930 (arb. units)
3D surface of green luminescence of Gd2O2S:Er 6% versus time and laser-diode current, 980 nm excitation
Measured dataScale to 830 (arb. units)
3D surface of green luminescence of Gd2O2S:Er 6% versus time and laser-diode current, 1550 nm excitation
Measured dataScale to 540 (arb. units) · telecom band
3D surface of green luminescence of Gd2O2S:Er 6% versus time and laser-diode current, 808 nm excitation · control
Measured dataScale to 500 (arb. units)

The same crystal answers 808, 980 and 1550 nm light, and each wavelength leaves a different shape of response as power rises. That is the kind of fingerprint an IMS reader is built to check.

Measured data · thermal phosphors

The crystal is also a thermometer.

Heat a rare-earth phosphor and its light changes in a predictable way. In this IMS thermal-phosphor project the blue band near 455 nm grows steadily against the peak at 493 nm, from room temperature all the way to 1,100 °C. The ratio between the two is the temperature, read by light alone: no wires, no contact, through a window or into a flame.

Measured data
Intensity (a.u.)
Emission spectra from 440 to 515 nanometers at temperatures from 26 to 1100 degrees Celsius. The band near 455 nanometers rises with temperature while the peak near 493 nanometers stays fixed.
Emission spectra of an IMS thermal phosphor from 26 °C to 1,100 °C, normalized to the 493 nm peak. Markers show the 455 nm band at the selected temperature, read from the figure.
Temperature
26 °C455 / 493 = 0.06
264007009001,100 °C
26 → 1,100 °COne ratio covers room temperature to the inside of a furnace in this data set.
~1% per °CChange in the rise time of Y₂O₂S:Yb,Er powder between −50 and 100 °C, in the 2018 study below.
One detectorRise and decay time sensors are not fooled by smoke, dirt or a tinted window that skews colors.
Publication · co-authored by IMS MRS Advances · 2018 · Materials Research Society Thermal and optical characterization of upconverting thermographic phosphor polymer composite films F. Sabri, S. W. Allison, M. Aryal (University of Memphis; Emerging Measurements), J. Collins and H. Bell (Intelligent Material Solutions)

Y₂O₂S:Yb,Er and La₂O₂S:Yb,Er were set into flexible silicone (PDMS) films and read with a 980 nm laser from −50 to +200 °C. Brightness, rise time and decay time all tracked temperature, making a thin, bendable, reusable temperature sensor. It is the same rise-and-decay clock we use to code a crystal.

Read the paper ↗
Same crystal family, 55 years apart

Gd₂O₂S was already glowing in this building in 1971.

In March 1971, P. N. Yocom, J. P. Wittke and I. Ladany of RCA Laboratories in Princeton reported that rare-earth oxysulfides, La₂O₂S, Gd₂O₂S and Y₂O₂S, efficiently turn the infrared light of a gallium-arsenide diode into visible green (ytterbium and erbium) or blue (ytterbium and thulium). IMS works today in the same RCA / Sarnoff building, and the crystal on this page belongs to the same family.

Publication · RCA Laboratories Metallurgical Transactions · vol. 2 · pp. 763–767 · March 1971 Rare-earth-doped oxysulfides for GaAs-pumped luminescent devices P. N. Yocom, J. P. Wittke and I. Ladany, RCA Laboratories, Princeton, N.J. Read the paper ↗

Inert crystals. Data sheets on request.

Intelligent Material crystals are inert, inorganic solids, used at tiny loadings inside inks, plastics, fibers and adhesives. Safety Data Sheets (SDS) and Technical Data Sheets (TDS) are available on request under a non-disclosure agreement.

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